Charan Ranganath
Appearances
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I believe that's true, but that's an opinion. I don't have data on that per se, but someone's probably looked at this. But that would be my sense is that a lot of what happens with the way people's lives play out as they get older have to do with their environment and their experience. And that's not to say that
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I mean, yes, neuroplasticity does change as you get older, but it doesn't account for the degree to which sometimes people can get stuck and set in their ways. And, you know, your example of the scientists is such a beautiful example because I look at the scientists who don't get stuck in their ways, right? And they constantly challenge their beliefs.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
They surround themselves with a diverse group of people who stimulate them, and they're also open to prediction error. That is they're open to saying something could be violating my knowledge of the world or my understanding of the way the world works. So here's just an example and this is – I know I'm going to be free associating all over the place.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Get into that. But it's like one of the coolest studies that we ever did and I totally credit my postdoc, Matthias Gruber, for this. He came into my lab recently. He's originally German, came in from University College London, and he told me he wanted to study curiosity and its effect on memory. I'm like, this is just – I am being totally closed-minded. I said, this is just a dumb topic.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You know, it's – everybody knows if you're curious about something, you'll remember it better. It's just because you're interested, right? So he said, no, no, no. This is really interesting. And so he did this experiment. And I got on board with it. We really kind of collectively, it was just this beautiful thing where I was exposed to something new and I got excited about it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so the idea was we would give people these trivia questions. And so it's kind of like a pub quiz, right? You sit in a pub quiz. Sometimes you get a question and it's like, I don't know the answer. Sometimes you get it and you go, I know it. Sometimes you go, I don't know, but. God, I really need to know the answer to this. And you get this itch, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Or sometimes your listeners, I mean, they're probably very curious people. That's why they listen to this. And maybe some of them go to your show notes afterwards because they want to learn more, right? So we actually scan people's brains using functional MRIs. And so we scan them when they get questions, and sometimes they had said, I'm really curious to find out the answer to these questions.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Sometimes they weren't curious. And then we make them wait about eight seconds or ten seconds, I think it was, something like that, and then we show them the answer. So they're kind of in suspense, kind of like you're watching Breaking Bad or something back in the day, people at commercials. And so you're like, oh, no, I got to find out what's going to happen to Walt, right? So you're in suspense.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You need to know the answer to this. Or you don't care. Sometimes you just don't care. You're just sitting around. So we show a little face and we say, hey, how likely is it you think this person knows the answer to the question? Now, this is a totally dumb thing to do because they don't know this person. They're just looking at a face. They're just making some arbitrary decision.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But I'll get to why we did that, because that was, I think, the coolest part of the experiment. But let's first get back to the trivia question. So we found that when we looked at brain activity when we give people the question, right afterwards, there is a burst of activity throughout the so-called reward circuit of the brain. It's not really a reward circuit as we've discussed offline.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's really these areas of the brain that process the neurotransmitter dopamine. And unlike many other neuromodulators that go all over the place, dopamine is much more restricted in its effect. And so in the midbrain near the ventral tegmental area, Sorry, I'm geeking out on this.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah. And so when we look at functional MRI, we can't measure dopamine. But what we see is activity in the dopaminergic midbrain area, meaning the area of the brain around the midbrain. And you see it in the nucleus accumbens or what's called the ventral striatum, which is another area that's super high dopamine reward processing area. The more curious people are, like on a one to six scale,
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
the more activity you see. It's just like this beautiful relationship, right? And it's not driven by the answer. Now there's a reason we probably didn't get it for the answer, but it's driven by the question. So it's not like they're like, oh, I learned something new. It's like, I want to get this knowledge. And so that's part one of the story.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Part two of the story is we show that face right after the question. And if people are curious to find the answer to the question, they get a bump in memory for the faces relative to if they're not curious. Now, the faces have nothing to do with the trivia question, but it's being in that curious state that drives this dopaminergic activity in the membrane.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So there's a whole lot of other studies, findings from that study. But basically, I think, God, I got to, you know, sometimes you do a lot of studies. I mean, I've published a like 180 studies.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So it's like, I'm trying to remember the exact, I think it was like functional connectivity between the hippocampus and the red brain during the face was predicting better memory for these faces in general, something like that.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Beautiful synopsis, but I'll do two cheerful amendments. So one is technically we're not measuring dopamine, so I have to be very clear about that. This is bold signal, meaning it's metabolic activity, but it's following all the usual suspects of where you'd expect it to be. The second thing is I do think that dopamine is playing a part. And I mean, it definitely facilitates plasticity.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So I do think it helps in learning the answer for sure. And there's a whole theory called synaptic tagging, which basically says that if you just release a bunch of dopamine and then you have these potentiated synapses, that you can drive plasticity in those synapses, even if it's not happening at the same time. But what's really cool is the face has nothing to do with the trivia question, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
The theory that we have is when you get that bump in dopamine activity, you're motivated, you're energized to get the answer, and you're driven towards a state of plasticity. And now giving you something that has nothing to do with this question, and boom, you got it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Older people show the effect just as much as younger people do. Kids show it just as much as older people do. It's just something that sticks around. So, I mean, speaking to your point, If you are surrounding yourself with things that will stimulate your curiosity, and if you're open to that curiosity, and we could talk about knowledge gaps and all these things that stimulate curiosity.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Novelty is another one. Richard Morris has some beautiful data on this with rats, but Emer Dussel and I, too, have some data with humans. surprise, all of these things. I have a whole chapter in my book on this. Drive that system.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
The dopamine system. So basically, if you expose yourself to opportunities to be proven wrong, you expose yourself to new people, places, situations, and you allow yourself to be energized by these things and not be scared and anxious, not be like, oh, this person's saying something that I disagree with. I can't deal with this, you know? Or, oh, we figured this out 30 years ago.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
We don't need, nothing's new here. If you can be open to that, I would argue that you're going to be engaging lots of plasticity, and that's something that's preserved in old age.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Huh. That's a really interesting question. Yeah. Well, first of all, I want to be careful and not to say dopamine does this because it's a trap, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I wouldn't be exact and just say that assigning a single function to a chemical is risky, but that said, I do believe there's a link. One of the things that you see is in Parkinson's disease, dopaminergic neurotransmitter emission is shot, and depression is also a symptom of Parkinson's disease, it's quite a severe one in fact.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so what I think one theory goes is that dopamine energizes us to seek rewards or to seek information, right? So a big part of movement is you move to get something. it's approach, right? They talk about approach and avoidance as basic kind of things that you want to program. And so a person with Parkinson's disease has a problem with willful movement, tremors and stuff too.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But I think that dopamine is involved in this kind of energizing you to move. I think it's involved in energizing you to seek information. I think it's involved in energizing you to seek rewards. And so I do think there's some kind of a common pathway there. And it speaks to this issue of the difference, which you've talked about, and I talk about a lot, as wanting versus liking.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so Kent Barrage at Michigan has done great work on this. gobs and gobs of manipulations of dopamine activity. And what he finds is an animal, let's say, that is deprived of dopamine, it will go for rewards just fine. It just won't work for them. It won't do the work that you need to get a reward. But if you just put it in front of them, they'll take it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So what dopamine – it is heavily involved with these opioid systems that does drive reward responses and it's heavily involved in learning about rewards. And that's why you get a big dopaminergic bump when an animal gets a reward because you're learning about the reward and what predicted the reward. There's a little bit of a credit assignment process that takes place.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
What's interesting is you get this too with actually my colleague at Davis, Brian Wilchin, some beautiful work where he's looked at trace conditioning, which is when you have like a – let's say if you play a tone and you wait a long time and then the animal gets a shock, right? And so what you find is that the animal learns to be afraid of the tone. But it's such a long time in his thing.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I think it's on the order of 10 seconds or above. the animal has to be somehow doing something to be able to blame that tone for getting shocked, right? And so what he found was that there's this burst of dopamine activity in the locus coeruleus, which is actually known for norepinephrine, but there's really cool work on dopamine in the LC now modulating hippocampus. Sorry to get all nerdy here.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yes, that's right. And sometimes they co-release from the same neurons, from what I understand. And so what seems to be happening is, and he's studying this now, but what seems to be happening is it's not that the animal's going, oh, I just heard a tone, I heard a tone, and then they get shocked.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
it may be more like they get a shock and then they get an immediate what just happened and then they get a memory retrieval of the tone and that allows them to put the two together to learn that this tone caused the shock, right? And dopamine seems to be playing a part in that learning process too. So it's not just about reward.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's really kind of, you know, the next time you hear that tone, you might, if it were a real threat, you could actually escape from it, right? And there's this whole active avoidance literature that you can look at with these approach circuits that are actually quite useful for avoiding threats and avoiding punishment. So it's really, to me, I see this role for energizing.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And that's often rewards. I mean, I like rewards as much as the next guy, right? I mean, look at how much coffee I drank when I got here. So it's not that, but it's just that it's mobilizing you, I think.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah, yeah. I mean, to me, I talk about this a little bit in the book, but to me, and if you look at the literature too, you can see this, a big part of being curious is the appraisal process, so to speak. And what I mean by that is saying— So something happens, right? Let's say something in your environment happens. If you're going to – you have a decision to make. Is this interesting?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Is this important? Is this scary? And I think the thing is, is that you need to be open to that possibility that it's interesting. So let me just give you like an example that I often give. Let's say you're walking in a neighborhood, you're traveling like you do for many of your events, and you walk into a new neighborhood you haven't been to.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's nighttime, kind of poorly lit, and you hear a loud noise, right? You could be like, well, that's a gunshot. I better hide or I better run. Or you could be like, oh, maybe there's a club nearby and there's like a cool band playing. I should go check this out. that appraisal is really critical for how you respond. And so it's not just a matter of curiosity happens.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's a process of cultivation and it's a process of appraisal. And so, I mean, this is, I think, I'm not a wellness guru or anything, but it's like I think this is one of the cool things about mindfulness training is it forces you to take the mundane and be curious about it. And when you start paying attention to your breathing, my friend Mishi Jha has really kind of turned me on to this.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
She wrote a book on mindfulness and meditation. And one of the things that happens is you're breathing and you realize, wait a minute. This one isn't the same as the last one, right? Or you can do these meditation. I'm sure you've done this, right? This part of like the sound is different. I'll sit in the backyard doing, thanks to you, I do this morning 10 minute thing.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so I'll be out in the backyard and I'll be like hearing some sound and I'll be like, oh, that sound, there's a bird there. I didn't even notice that, you know? And then there's some other sound. I'm hearing the freeway. That's annoying, but I heard it. And so these, it's really a matter of, paying attention in some ways and being open to it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And I think this speaks back to this thing about as you get older, sometimes people find it scary to be in a new place. People find it scary to meet a person who's different from them or so forth. I mean, I love listening to music that's a little bit out of my comfort zone. Some people hate it, you know? So I think some of it is sort of cultivating and being comfortable with discomfort.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, first of all, I'll add a whole lot of other neocortical areas we can talk about.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, so the hippocampus is controversial. I mean, it's the most studied area of the brain, arguably, except for maybe V1. Visual cortex, V1.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I believe – and my colleagues do. I wrote a big paper with Howard – the late Howard Eichenbaum and Andy Olenas on this who – from Davis. And we believe that it's about linking various experiences to a context. And what I mean by that is you've got information about smell, high-level vision, high-level semantic knowledge information, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And the hippocampus' wiring is really set up to not understand what's going on. So the late David Morrow's pioneer in computational neuroscience proposed that what the hippocampus is about is what he called simple memory. It's basically saying... I know Andy Huberman. Sorry, is that okay?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You would understand. So I know Andy Huberman, right? But to have a memory of this moment that's separate from, let's say, I saw you at some neuroscience retreat when you were in grad school, I have to have some part of the brain that doesn't know who you are to some extent, right? Because I got to keep them separate.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so there are – the hippocampus, what it will do is it will form a memory that's not an Andy Huberman memory. It's an Andy in this place at this time in this context. And that's what allows it to support what's called episodic memory, which is your ability to say, I went to Washington, D.C. once and I remember going to the Smithsonian.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
as opposed to your knowledge about what generally happens in Washington, D.C. Oh, the president's there. Oh, that's where a lot of politics happen. Oh, the Smithsonian is a place in D.C. It's a memory of your being there at a particular place and time.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Now, there's other parts of the brain that allow you to associate that information in a meaningful way and to be able to actually expand on that context and create these narratives and these stories about it. And where the prefrontal cortex comes in, and it's a huge area, it's about one-third of the primate brain. So it's just massive.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
There are a lot of people who go, well, there's a bunch of different areas and I'll do different things. And I subscribe to the view that that is very true. And at the same time, there's a global function of the prefrontal cortex. which is what's called cognitive control.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's this ability to say, I'm going to regulate my movements and I'm going to regulate my perceptions and my thoughts based on what's important to me in terms of this higher order goal, right? So when I've tested, for instance, patients with prefrontal lesions, I'm sure Mark Desposito talked to you about this,
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's like the hallmark of them, they used to say, well, the prefrontal cortex, it's important for working memory. And you could record from neurons in the prefrontal cortex or look at fMRI signal. And if a person or an animal is holding something in their mind, like a phone number,
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
neurons or bold signal and MRI will be highly elevated, their activity will be elevated throughout this period of time where they're holding in mind. But it turns out if you just ask somebody with a major prefrontal lesion, here's a bunch of numbers, 5, 2, 7, 8, you know, I ask you to tell them back to me in right order, they can do it just fine. But now I start to distract them.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I move my hands around. There's a plane going on, flying outside the window. I mean, I had that literally happen once. Now they start to vomit because their attention is not controlled by their goal. It's controlled by the environment around them. And so this is where things get really interesting. So I once tested a patient and I'd heard about this, but until you see it, it like doesn't register.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It really blew my mind. So- There's a test called the Wisconsin Card Sorting Test, and we don't have to get into all the details of it. But basically, it's this test where people learn some rule about where to put a card on a table, right? And they don't get told the rule. They just learn it. And patients learn this prefrontal damage, learn it just fine.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. Yeah. So maybe I'll give a little bit more background, but I don't want to go in the weeds.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, exactly, exactly. And you don't need a prefrontal cortex to do that, which is surprising, but you don't. You can do it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yes, but let's unpack this context thing, right? So now you've been, let's say, putting all the diamonds in one pile. You've been putting all the spades in another pile, right? So now I change the rule, but I don't tell you. And you put the diamonds, the queen of diamonds in the diamond pile, let's say. And now I say, nope, that's wrong.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So now you have to say, wait a minute, that was right all this time. What's going on? This is like life. This is like life, right? The thing that used to work for you no longer works. So you keep doing this, and a person with an intact brain will eventually figure out, okay, that's not working. I'll try another strategy, and then they'll learn the new rule, right? It's not easy.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's a pain, but people will do it. This patient in particular said, kept on using the old rule. And so you have to give a series of hints going like, hmm, what's your strategy here? And they're like, they'll tell you I'm putting it according to the color. And then you, okay, well, does that appear to be working for you? And they'll go, no. And they'll just keep doing it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
They perseverate. But the interesting thing is he knows it's not working. Yeah. But he can't help himself from doing it. And so what the prefrontal cortex is, it's not about this declarative knowledge about what you should do. And I think this is very deep because I think often we get moralistic about people's actions, especially for people who have head injuries or something like that.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And it's like you can have all of these beliefs that you want to have, but you need the prefrontal cortex to translate these high-order beliefs, things that are very abstract, into actual concrete action. Otherwise, what you do is not going to be dictated by that knowledge. So how this relates to memory is— We're constantly barraged by information.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I think it's, I might've said something like 35 terabytes. I don't know, but it's a big number and the estimates get bigger and bigger every year. So we're barraged by information. There's no way you can even pay attention to it all, right? So you really rely on the prefrontal cortex to be able to say, this is what I'm doing right now. And everything else, it's noise.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Here's the signal that I need to focus on. And that's super important for memory because one of the things you see in old age is older people are bad at most memory tests. But it turns out in labs, we kind of overestimate that. And the reason we overestimate it is we're giving them a test, which is something hard. It requires a lot of focus, and it's not something they do every day. But
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Karen Campbell and Lynn Hasher, these great cognitive psychologists, did this cool experiment where they had a bunch of other stuff that people were supposed to ignore in this memory task where they're studying a bunch of things. They're trying to memorize a bunch of stuff, but there's stuff going on they're supposed to ignore.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
The older people were just as good as the younger people at remembering the stuff they were supposed to ignore. They were just bad at the stuff that they were supposed to pay attention to.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
They were bad at remembering the stuff that they were supposed to remember, but they were just as good as the younger people, maybe even better, but definitely as good as the younger people at remembering the things that they weren't supposed to pay attention to.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. Well, OK. I should say the benefit of curiosity on memory is intact in older people. I got that wrong. I don't know. Matthias could tell me if I just email him at a break or something. But I don't know if curiosity itself is as high in older adults, self-reported or –
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Don't know, but I can say two things to this. One is that definitely there's a lot of work on media multitasking. And the short answer is bad for memory.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, media multitasking is bad for memory. The tech thing is a super fascinating area in general. It's really how we interact with the tech that's bad. But If you're an older adult, your frontal function is not going to be as good. You will be more distractible. You will be more likely to go off course.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so that scrolling is going to be more potent because, as you pointed out, the algorithms are all designed to suck up our attention. So psychologist Herb Simon came up with this beautiful term called the attention economy, right? Mm-hmm. And so the idea is that the more information that you have in front of you, the more impoverished you are in terms of your attention.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So there's no such thing as free speech because it's like you have a limited supply of attention. So everything has a cost. And so the more information you have in front of you, the harder it is to pay attention to what's important. And that's where I think the older adults really lose some of their functioning because basically –
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I talk about in the book, and it's not a perfect analogy, is neurons are functioning kind of like a democracy in the sense that, you know, real democracies involve these political coalitions or alliances, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I mean, people talk about the right and the left, but that's dumb because it's like there's always just alliances between people who like different things, and they just form these convenient alliances with each other. But let's just imagine neurons kind of do this in the brain, right? And so you have...
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
in theory, to be able to pay attention to something, some coalition of neurons has to be firing a lot that is corresponding to the thing that you're trying to pay attention to. But if something is salient, bright, shiny, loud, it's just grabbing your attention.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
What's going to happen is that those neurons start to shout down the neurons that are trying to keep you on what's not shiny, but it's important, right? And so what happens is with the prefrontal cortex, you can bias that competition. That's the term that people have used in literature.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
That allows you... So what people have found, for instance, just a really cool finding again is you can find in the visual cortex neurons that fire when you're seeing something red. Neurons that fire when you see something blue, let's say, right? I'm kind of distorting the picture, but you get the idea.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So if an animal is trying to hold in mind something, I'd say hold on a mental picture of something that's blue, what happens is the blue neurons are firing in the visual cortex, even though the animal's not seeing blue, right? It's just they're thinking about blue. You damage the prefrontal cortex... Nothing. So you lose that selectivity.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So what's happening is the prefrontal cortex is biasing the competition and saying, I know blue's not shining in front of you. There's no shiny blue thing in front of you right now, but I need these neurons to stay active. And so it's doing this modulation to help out the neurons that are keeping the information in the skull relevant.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So what happens when that communication goes, let's say, due to hypertension, diabetes, you get all this white matter damage that happens with old age. And this is really a big thing that is very preventable with the right protocols, so to speak.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Exactly, yeah. And so... If you damage those long-range tracks, the prefrontal cortex is not efficiently able to bias that competition. And so now the inane gets remembered at the expense of the important. That's, I think, the key thing. And that's why people talk about the prefrontal cortex as the central executive. As anybody who's worked a job knows, it's like the executives are useless, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You try to get an executive... I mean, except for some who are useful, but then they don't really run companies very well.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, well, okay, we won't go there. Controversial, shall we say. But anyway, so like a good executive, their job isn't to micromanage. Their job is to say, here's the big picture, here's my vision for the company, and I want everyone to be working towards this goal. not sifting through the mailroom, not paying the bills, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so what happens is that when you have certain kinds of things that happen with aging, like damage to the white matter, that happens through essentially tiny cerebrovascular events, most likely. And we've done some research on this in our lab in collaboration with Bill Jagus, who's now in Berkeley, and Charlie DeCarli. And
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You can measure this in MRIs with a measure called white matter hyperintensities. You use a scan that shows up little bright spots where the white matter is probably damaged. And what you find is that these people with white matter hyperintensities actually have memory performance that's as poor as people who have hippocampal atrophy probably in the early stages of Alzheimer's.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And they're also bad at controlling information even when they don't have to remember something. So it's like a double whammy. And it's kind of like the executive is trapped in a remote place and they got no internet access and no phone. And so they can't communicate with the company as everybody's just doing their own thing, right? And that's a little bit of what can happen with aging.
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Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It doesn't have to, but that can happen. And you see this to a really great extent in many disorders. This is why so many disorders really affect control and frontal function, multiple sclerosis, diabetes, many kinds of things. We talked about brain fog. Many kinds of inflammatory conditions will affect it. Depression, clinical depressions. I've seen people, older adults with depression,
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
who are cognitively more impaired than people in the MCI stage of Alzheimer's.
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Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's terrible for memory. And it seems to be a risk factor for Alzheimer's as well.
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Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I would probably not say that. And I would say also, I don't know what, I mean, you know, once you kind of get into these things in the epidemiological world, everything interacts with each other and there's genetics and there's environment and blah, blah, blah.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You know, I think that's a big part, but you do. Okay. So let's go back to your question because I do think curiosity is affected by I don't know the research on this, but I would be shocked if it isn't. And I do think that dopamine activity is disrupted in depression.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And your motivation to get anhedonia is one of the hallmark symptoms of depression, as is rumination, by the way, which is memory retrieval of preferential negative retrieval of negative events and cogitating over them.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I mean, as a memory researcher, I almost find myself ashamed when I talk about these things because, as you know, so many of the most important factors are ones that are related to just health. So for instance, you mentioned sleep. That's a big one. Actually, there's a beautiful study that speaks to this that was done, 29,000 subjects in China. And they followed them up for 10 years.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Now at the beginning of – so they divided people into three groups. They said, OK, here's – well, what they said is there's six lifestyle factors that we're going to investigate. One was I think engagement in cognitive activities. I think one was social engagement. One was physical exercise, not smoking, I think no alcohol.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But they identified these lifestyle factors that were basically just kind of good lifestyle factors. So they get people who have four to six of these lifestyle factors going versus zero to one of these lifestyle factors. We'll just take the extreme. When they start, they're all the same.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
10 years later, the people with four to six lifestyle factors going for them are performing almost twice as high on memory tests as the people with zero to one lifestyle factor.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah, definitely not smoking. And smoking and alcohol, I think, were big ones.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, let me, by the way, I just have to say I forgot healthy diet. Healthy diet was a big one too.
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Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah. So I was actually emailing with Dean and Aisha Shirzai, who really talk a lot about this.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
They do great work. And so they were actually sending me some stuff, and I had known about some of this. But, like, Mediterranean diet has worked really well.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. Which I think, you know, let me come back to this point because I think it's super important, but leafy greens were a big one.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
They pointed out a Rush Presbyterian study that I didn't know about that put people on, I think it was called the DASH diet and it included leafy greens as a big part of it and that had a dramatic increase in cognitive... I mean dramatically preserved cognitive performance in people who were on that diet. So the healthy diet is a big part. Now, nicotine is interesting.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So if you notice, a lot of people with schizophrenia smoke. And one of the things that's been found is that nicotine does seem to improve functioning in people, cognitive functioning in people with schizophrenia. Now, I think the big thing to remember about any kind of drug – and this goes for food effects probably too but especially drugs – is there's huge individual differences, huge.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so, I mean, just to give you an example – I could not function without that coffee that I had this morning and then coming in here. But my daughter would not be functional after those cups of coffee. Some people really are affected by these different things differently. And then, of course, there's always a dose-response curve, and they often follow these inverted U's.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So Mark Desposito, who was my postdoc mentor, did a lot of work with dopaminergic drugs. And a lot of people had done these drug studies early on on cognition. They would find no effects or sometimes it would make people worse.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And what he found was that if you looked more carefully, there was an inverted U effect where some people, and it depended on their working memory capacity, were actually benefiting from the drug. And then these other people who were, let's say, I can't remember if it was higher or lower, were doing worse. And there's a genetic component to that, unsurprisingly.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Dopamine transporters play a role and so forth. And so now you start to get into all of these gene, environment, drug interactions that are just – I would really caution people against saying nicotine is good, nicotine is bad. I think it really, really is a much more complex issue, just like marijuana, right? So you can look at smoking weed in adolescents.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
For people who are at high genetic risk for psychosis, it dramatically increases your risk for psychosis.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Maybe cut out any misinformation I might have said in the end.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I mean we're now interestingly seeing this with psychedelics where it's like all these positive effects of psychedelics are being brought up. But a lot of people remember – The negative effects on people like Rocky Erickson from the 13th Floor Elevators or like Sid Barrett from Pink Floyd, who became psychotic after doing large amounts of LSD.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Rocky Erickson from the 13th Floor Elevators. Great psychedelic band.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. And of course, sanity is in the eye of the beholder too. But what I'll say is that, yeah, and you can see this actually, there's some new concern about Adderall and stimulants. And if you're giving it to people who might be at high risk for schizophrenia, it might also promote psychosis.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
We do. We do.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, exactly. So it's really a much more complicated interaction and I think this is where this whole realm of personalized medicine will be super helpful. But there does seem to be a broad general effect for certain dietary interventions. Berries seem to be good. Leafy greens seem to be good.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yes. Yeah. Actually, so I, like, when I finished my book, I limped to the finish line. I had all sorts of crazy stuff happen. I won't depress the readers with all the crazy stuff that happened.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Probably. I mean, I don't know. I probably lost some, like, biological years in that. But it was really, like, I mean, it was great. I mean, it was really an emotional roller coaster, though. But then I had a bunch of, you know, I'm trying to do science, write this book basically in my spare time, which doesn't really exist, as you know how it goes. Sure. And then I had life happen.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You know, my mom was in the hospital. My cat died on my birthday. I mean, it was just like, yeah, see, I didn't want to impress people with all this stuff. It's real life.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. No, no, no. It's OK. So then I finished my book and I was like just thoroughly thrashed. And I had a sabbatical because I wanted to have time to promote the book and educate people about what's in the book. And which I'd never gotten a chance to do before. It's like doing this. Fantastic, right? I get to talk to people. So I really wanted to make some changes.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And actually, this gets something we were talking about before we started recording, which is after I wrote the book, it's all, you know, it's going in the proofing stage. I was talking to my daughter and just, you know, out of the blue, she said, we're talking about ADHD. And she's like, Dad, you totally have ADHD. And I'm like, what? What?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And I'm like, oh, Gen Z, overdiagnosis of ADHD, whatever, right? And then I remembered when I was a kid, my school contacted my parents and said, you have ADHD. He has ADHD. And it was interesting because it was like I actually was ahead in school by a year, and I got held back because I just was so socially bad. I couldn't stop talking in class and I was just like really awkward and impulsive.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so, but it was the 70s, nobody did anything. And I had all sorts of behavior issues and so forth. And there are other factors going on too. But it really got me thinking, oh my God, I got to make some changes. I'm living this unsustainable life where I'm jumping from crisis to crisis to crisis. And I say, I don't have time for blah, blah, blah.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so my, again, it's going to sound depressing, but it's got a happier ending. So my dog had died in 2019 of cancer. And that was my first dog. And so I thought, I'm never getting a dog again. And in 2020, in the pandemic, I got another dog.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. What kind of dog? Both of these were shelter dogs.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
They're all mixes. I'm sure there's some pit bull in her because every shelter dog either has pit bull or chihuahua. But she looks very Belgian Malinois and she moves like a Belgian Malinois.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. And they're so smart and super athletic. I mean, she can like jump vertically, you know, just like it's so like it was all come home. She'll like jump up and then push herself off me, which is like a very classic thing. And so that's why they can jump like she can climb up like seven feet up a tree to chase a squirrel.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah. But she's a smaller dog, so our older dog looked like kind of – she wasn't. She was actually a Kelpie mix, I think, but she looked like a Rottweiler. And so everyone was scared of her, even though she's the sweetest dog. This one, she's like smaller, even though she looks kind of shepherd-like. Everyone's like, oh, your dog is so sweet. She's so cute.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Exactly. Yeah. I mean, all sheltered dogs have a little bit of a crazy switch in them, don't they? It's tough for them.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. Yeah, exactly. And one of the things that I was thinking is I missed walking the dog. I missed that activity. And so I make sure to do that every morning. And this goes back to some of the activity things that we're talking about. I know I'm totally drifting away from ADHD, which is ironic.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, but this is a little bit different, but it's related, which is having a sense of purpose is very important for healthy brain aging. There's a Trends of Cognitive Science article I could send you. It's one of these things that neuroscientists don't talk about because it's not...
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
We don't understand it, but it's hugely important as part of this whole phenomenon, what they call cognitive reserve. And, you know, having this dog that I'm taking care of, especially because, you know, my kid had gone to college, he's grown up living independently. walking this dog every day. I mean, obviously I'm married and I love my family and I've got lots of them.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I love my students and so forth, but it gave me more and I'm exercising in a way that's kind of fun. I'm listening to podcasts and I'm moving. And so that's something right there. It's not just the exercise, but it's the whole thing, right? I'm not doing something that I hate. So then I'm like, I hate running.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I hate, I have this inertia because my ADHD brain doesn't like to do stuff unless it's shiny and fun, right? And I could go into work, I could write this book because it's fun for me, you know? But so I'm like, how can I do this? And so I ended up shelling out for a personal trainer. I blew my advance on a personal trainer who's great.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And I go to see her and she tells me what to do so I don't have to think about it and it's fun.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Okay, let's not attach that saying to me. It was a joke.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
If you're out there anywhere, don't hate me.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
To me, and again, you know, I'm not a social psychologist, so this is a little bit out of my wheelhouse. But to me, the sense of purpose is kind of this existential thing of like, you know, I got to take care of this dog. And I got to, you know, and when I look at this dog and she's moping around in the corner, I feel bad. But I feel like it's my responsibility to do something with my students.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
With my students, I have, you know, I had was very, very fortunate to have many people leave my lab after the pandemic, which destroyed so many careers and many people left my lab and I got faculty positions. I'm like so happy for them.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, thank you. You do well because you have good people in the lab, as you know. That's true. But what was interesting was I had finished the book and my lab was relatively empty, and I did feel purposeless. I felt that absence of that sense of this bigger thing.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so part of the work is, you know, and this was like a thing that I felt doing the book promotion is I feel a sense of purpose in explaining science to people. I got an email this morning as I was getting on the plane from somebody who was asking me a question about memory. And I was just like, this is so cool.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You know, after you spend years lecturing students and some of them are sleeping in class and You wonder, is anybody really impacted by this? And it's just been a beautiful thing. So that gives me a sense of purpose.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I've come up with – I've really rededicated myself to research and we're doing these huge computational models of learning and I'm trying to get – we're doing VR stuff and we're going to be doing all sorts of new things in the research. And that gives me a sense of purpose.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But a lot of it to me about the connection thing that you bring up, it's super important because often I find myself, again, because of the ADHD thing, for all of these things that I like, there's things that you have to do that suck. And for me, that suckiness is utterly painful.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, it's interesting. I mean, first of all, it's a great question to start off with. And it's interesting because I actually don't think memory is about the past. I think memory is about the present and the future. It's about taking selectively what you need from the past to make sense of the present and to project to the future. I know you're a vision guy, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I mean, and I know there's a lot of people like, I know ADHD is over diagnosed right now for reasons that are interesting. And I know a lot of people, it's very kind of fashionable to say stuff, something like that. Maybe, I don't know, people can be judgy about this stuff. But for me, it really is painful.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I mean, I've actually found that it's hard for me to work with certain people if they talk slowly. I mean, it's that tough. So I've really had to think about – so I actually hooked up with an ADHD coach who has been phenomenal for me. And I know coaches are another controversial thing.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah. Well, you know, I mean, I didn't know what to expect because it's like an unregulated world, so to speak, or minimally regulated. But the person I found was just amazing. And the first thing she had me do was she put down, had me write down a sheet of all my values. and order them and rank them. And so I'm thinking this is such a waste of time.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Sorry, Lori, but I was thinking initially, this is such a waste of time. Why am I doing this? I don't really value it. I don't know. I just do things. I don't necessarily value them or whatever. But then I started writing them down. And then later I was talking to her about like this, you know, some of my troubles with motivation and getting things done that I don't want to do. And
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I'm kind of infamous for having trouble getting things done that I don't want to do in terms of like administrative tasks and so forth.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, it's true, I guess.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. So basically it's like – so then I put the two together and I said I'm not giving myself credit for why I'm doing this. So this goes back to the whole – I mean in a way it goes back to the prefrontal cortex conversation is – What's my goal?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
If I'm going to see someone and have a meeting and I don't feel like going to the meeting because I'm tired and I'm bored or I want to just look at this YouTube video or I want to go on social media or whatever dumb thing that I waste my time on, right? I say to myself, well, why am I doing this?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And I remind myself of that motivation and it kicks everything in gear because now I have that goal in place because the goal just doesn't pop up for me automatically. And so relating what I do to values is a game changer for me. But it's a conscious thing that I have to work on to remind myself of those values and connect them.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And that's part of what I think people lose when they retire, for instance. I see this in people I'm close to who have retired. They feel like work is their only purpose. And so afterwards they feel purposeless and then they're just doing things like doom scrolling or being radicalized on the internet or like going into – but it's just like whatever captures their attention.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And I think – so a big part of that sense of purpose for me has really been to get in touch with what do I really want. And I mean this goes back to another thing with memory. And I know this is a total ADHD pre-association thing, but it's like I can – people often ask me, okay, fine.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so if you look at people's just eye movements, right? The first time I came into this room, I'm sure I wasn't aware of it, but I'm sure my eyes were going all over the place. Now, if I came back to visit, you say, if you're like, oh, that was an awesome interview or whatever, right? Hopefully, but maybe not. But let's say I do, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Give me all this stuff for brain aging and we didn't even get into hearing aids and vision testing and oral hygiene and so forth.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But what I tell people is – I can tell you lots of strategies for remembering names, for remembering where you've been, for trying to remember like to do something in the future, some of the hardest memory challenges we have. But unless you do them, do those strategies, I can't help you. And the problem is, and this speaks to, I really liked what you said.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
We do have to talk about some exceptions like retrieval-induced forgetting and some interesting things like the pre-testing effect. But your thing on study skills, I listened to that podcast and I was like, the beautiful thing that you did with that, one of them, was that you said, assume that you will forget.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Because if you go back to the earliest research on memory by Ebbinghaus, he tested himself. And he actually created these weird words called trigrams that weren't really words. He tried to memorize them. And what he found was within 20 minutes, he had forgotten about half of what he memorized.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
within, and I don't mean just forgotten like he couldn't bring it to mind, it took him as long to re-memorize them as it was if he had never done it, right? So sometimes we have partial memory where we can't recall it, but we get some savings and it's easier for us to learn. He didn't even have that for a lot of the stuff.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So then he waited 24 hours and he had lost two-thirds of what he had memorized, right? So translate this into the real world. There are some things that are caveats that we do better in the real world, I would say, at the big things, the gist of what we encounter. But the details, we lose most of them. Most of the details of your life will be gone.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And this is true for even – I would argue this is even true for people with highly superior autobiographical memory. I don't know for sure, but I can tell you more about that. This is true for everyone who's been studied as far as I know. And so – If that's the case, the question is not like, why am I so forgetful? It's why do we remember the first one? It's why they titled it for the book.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And the question is, what do you want to remember? What are the memories that you want to take with you? Whether it's memorizing things for a class, like in study skills, or whether it's your kid's birthday party, which I talked about in chapter one. Um, these are, it's about intention is what I say.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's the difference between attention, which can be grabbed by anything versus intention, which is saying, this is what I want to take with me. Right.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yes, it is directing your attention based on some reason that's an internal goal, right? And that's where the prefrontal cortex really comes in. So it's very easy in some ways to pay attention to me if I'm like gesticulating and I'm talking very loudly because it's grabbing your attention constantly. I mean, let's face it, I know lots of people in my life who hate this because I'm so loud and
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. So I go and my eyes will probably go right to the Rick Rubin photo. Then I'll go right to, you know, something else or to the espresso machine. And so my memory allows me to make predictions about where things are. And it's almost pre-conscious so that it's happening without our awareness. And it's like confirmatory.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I need like Huberman's like words of encouragement on my phone that I could just open up.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. And this is, by the way, this isn't a technical term. This is just, I like it because it rhymes and a friend of mine came up with it. So, but yes, intention is your ability to say, this is what's important to me right now. And that's why I need to pay attention to it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Hence the values list. Because if I don't keep that in mind, my, so we tend to think of control as being just like willpower or like, you want to do the right thing or whatever. It's not. It's really a big part. There's so many parts of it, really, but a big part of it is motivation. And motivation is not a trivial thing.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's not simply wanting to do the right thing, but being able to keep that value in mind and retrieve that value because everything has a value associated with, right? And sometimes things that are, you know, I'm thirsty and there's water in front of me, that has a big value and that should grab my attention. So it's not that...
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
having your attention shift, you want it to be flexible, but you want to keep these higher order goals in mind. And so it's this balance between stability and flexibility. Now, the key is, or let's get to your specific example of like technology, right? So ever since I got a phone, that is a smartphone, my first iPhone.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
We're grabbing the important stuff and making sure everything is where it's supposed to be. And you can see this play out in phenomena also like change blindness. And it's a little bit of a different phenomena. But basically in change blindness, there's a famous example where they show a video of people playing basketball and they're passing the ball back and forth.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Mine was, well, you did better than me, I think. Maybe it was around the same. It was iPhone 3, I think, was my first. Okay.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I think I had the iPhone 3, which was whenever that came out. Yeah. So until then, I would check email when I was at a computer. When I'm not, I don't think about it. Now it's always there and you get alerts on your phone, right? So let's play this out now. We're having this great conversation.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Let's say we leave, we talk about skateboarding and punk rock and like, yes, why didn't we talk about this on the podcast? We're having a great conversation, right? But now let's say I didn't put my phone on focus mode and I start getting all these little beeps on my phone. I know people. I know I played in a band with somebody who had ADHD.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And he would – anytime we were in a conversation, he would just check his text messages. Sometimes he would text in front of me, right? So what happens is every time you do that – you're essentially shifting your task, your mindset changes, your intention is somewhat changed by this new task, right? So now I've shifted and there's a cost associated with that.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
In fact, actually people who study this, there's like four or five different costs that go on. It makes you slower to do the new thing, right? Now I go back to the conversation. Well, now I have another cost associated with that. And so I'm not there where you are in this moment. I'm several seconds behind you, and I'm still catching up while you're talking.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And that requires even more control to get caught up and get back up to speed. So I'm straining my natural resources. I'm straining my cognitive control by shifting back and forth. But here's an even worse part of it. So a memory, we haven't even talked about this, but it's like a lot of our forgetting happens because we have these blurry memories. They're not distinctive. They don't.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You don't get a population of neurons that shouts out loud, hey, that's this conversation I had with Andy, right? It's just kind of this blurry sense of I talked to someone on a podcast. I'm not saying that this will happen now because it won't. So I have this blurry memory. Well, why does that happen?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, part of it is you have to catch the distinctive moments of these events, and you have to associate them together into this cohesive narrative.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
One of the things we found in our research and other people have found is when, let's say if you're watching a movie and somebody changes the topic of conversation or a character comes in, something that shifts your attentional focus and shifts your understanding of what's going on, you see this big peak in activation in the hippocampus.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And what that seems to be related to is encoding a memory for what happened up to that point. And so we call that an event boundary. And so once you have an event boundary, it turns out you go on to the next event and you have trouble remembering the stuff that happened right before the event boundary. It's why people end up in the kitchen and they're like, what was my reason for coming here?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And it's because they passed through three different rooms and their sense of where they were was changing, their mental context. updated to the point where now they have to work to figure it out, right? So this is what's happening when we are shifting between different tasks. I'm texting and I'm emailing and then I'm talking to you.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And then this guy in a gorilla costume just walks behind them. And about, I think it's 40% of the people who watch this video don't see the gorilla. And the reason is that you're generating these serious expectations about what's in front of you. And so you're not literally seeing what's in front of you. You are creating an internal model, a simulation really, of what the outside world is.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Or as you've probably seen in going to conferences, people, scientists, scientists who know better are sitting typing emails while someone is giving, I've done this because I'm attentionally impaired or I'm impaired. Actually ADHD is a cognitive control issue, I think, but Nonetheless, it's like I do this, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So it's like I get it, but it's like you are now creating this fragments of memories where it's not I have a cohesive conversation. I have a little bit. I got a little bit more. I got a little bit more. And those fragments of memory don't play together well in memory. They can compete with each other. And that competition is a big part of forgetting.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so that's why it's super important to just do one thing and then do another. If you want to do social media, fine, do it. then do whatever it is you are supposed to do for work, right? But it's the shifting that really kills you because it creates – saps your cognitive control. It actually creates these fragmented memories. It also actually increases stress levels.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So there's all sorts of things. I know there's a lot of tech bros who are just like, oh, no, I multitask. I'm great at it. You're not.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, and here's the thing, and this is really gets back to this idea of engineering your environment. And because so much of our lives, we're out of control, even though we feel like we're in control, right? And it's really, if I have a higher goal, sometimes you have to do exactly what you did, which is hack your environment to allow, to enable you to regain control, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So what I mean by this is it's like, I, even though I might not check my phone, I might have alerts off, If I have a habit, I'm thinking about it. And every time I think about it, that urge pops into mind. I'm getting a little distracted. I'm losing a little bit of executive control. So you don't even have to do it, right? You can just think about it. And multitasking is just one thing.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
There's other things. Like one thing I talk about in the book is taking pictures. So you've probably been to concerts. I know I have where it's like people are like just filming the whole things on their phone. Or like now you see the rise of Instagram walls where you go into places and there's a wall that exists so people can post to Instagram. Nothing wrong with this.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And memory, whether it's semantic memory, which we'll talk about, I'm sure, your knowledge about the world, like the cup thing, if it's episodic memory, which is your memory of what happened, let's say, just a minute ago, it's all coming into play in terms of your sense of where you are, right? If I just ask you, what day is it? You will use episodic memory for that.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But most – not all the research, interestingly, and I can get into why, shows that taking pictures actually impoverishes people's memory.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Let me be more specific about this, right? So let's say I'm mindlessly taking pictures. So I go in. I'm seeing the Grand Canyon. I'm just like, ch-ch-ch-ch-ch. A lot of people intuitively on average will say that they will remember it better because they took pictures. But what often happens is they're not really focusing on the distinctive elements of their experience.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
They're just grabbing as much stuff as they can. Let's take the concert as another example. If you are filming the concert and you're just trying to grab what's being sung, you will have a recording of the concert. But what's the memory you want to have? Do you want to have a memory of the song that you already can stream anytime?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Or do you want the memory of how you felt, the friends you were with, the connection that you had with the artist because you were there? I know this sounds real hippy-dippy, but it's real.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
In the sense that this is what you want to remember. I think, at least I don't want to lecture people if they want to remember taking pictures of things. That's fine. I'm sure everybody remembers taking pictures at these things, but what did you take a picture of? And so you can use the phone, and this is where the studies show good effects, is if I mindfully use the phone and I say, like,
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
There's something here that will be a good cue that will remind me later of this great conversation. I focus the camera on that. I take a picture mindfully. I use the camera not as a way of spreading my attention and just grabbing everything in this shotgun approach, but rather use it to find what's distinctive and what's important and actually focus me on it. That's a really good thing. Wow.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So what I try to do is selectively document, not over-document. I'll take a picture of people laughing or people eating. I like to go to conferences now. John Listman used to do this, late John Listman, and so he passed away. So now I try to do this. I think more about these things.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so I try to take pictures of people randomly, you know, they're drinking a beer and then they spit out laughing or something like that. And these are not... Things that are like landmarks that are not things that are tourist stuff, but they are great retrieval cues. And so what happens is the next part of it is seeing the picture. Well, what do you do when you see the picture, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Do you scroll right? Or do you use it as a cue to effectively test yourself to recall what happened during that event and integrate it? Now, what's interesting is that act of recollecting the event in itself will change the memory, right? and it can make it more accessible, but it can also make it a little bit more abstract and story-like.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Tomorrow morning, I'm going to wake up in a hotel room. If I don't have episodic memory, I will freak out because I'll be like, where am I? Did I get kidnapped? Why am I here? And that's really the experience of people with memory disorders. I mean, they have to be in really familiar environments because it's frightening otherwise, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so there is an interesting trade-off where you have these things where you have these memories and you could even document it. But if you use the, the, if the more you retrieve it, the more accessible it will be, but sometimes it'll be less immersive and more like a story that you've told a hundred times.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. Yeah, that's exactly what happens. People will remember something, but it's not their feeling. It's not like the friends they were with and what they talked about. It's more like – I used this example in an interview. So apologies if people have already seen this. But it's like I just – I got to see The Descendants. I'm guessing since you skateboarded, you probably had heard The Descendants.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So I grew up listening to them in high school, but I never got to see them because all the great bands I got into broke up right before Black Flag and The Minute Man and so forth. And so when they reunited, I was like – I had an opportunity to see them in a club in Sacramento. And so I saw them for the first time. And what was – I wasn't one of the kids taking photos. I was actually watching –
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But then there was a moment where Bill Stevenson, the drummer, who's a super intense guy and really one of the creative forces behind the band, he gets up and he starts walking towards the crowd. And Milo's like, sit down, go back behind the drums. And he's like, no, I want to say something.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And I was like, I got to take a picture of this because this is going to be like he's really connecting with us. And he talked about how cool it was to just be able to have this moment where he's now at this age able to appreciate this connection that he has with the audience that he couldn't appreciate before when he was younger.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And I was like, I'm taking a picture of this because that's what I want to remember. You won't remember everything. But if I look at that photo – technically, I haven't looked at that photo again. But just taking the picture of it forced me to really think about that. And that's – The biggest takeaway I have, you know, a lot of the songs they played, they did a really good job on.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But what I really took away from that was this connection that I really wanted when I was a kid, you know, and re-experiencing that feeling of being a kid and hearing these songs when they were fresh and new for me. And so that's – I know I'm sounding like kind of a hippie or something.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I got to digress all over the place.
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Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I wouldn't necessarily say that we were never seeing the present. Of course we are, right? But our understanding of the present is so informed by the past that it allows us both to focus on what's important, what's non-redundant with what we already know, and it also allows us to detect surprises and find out the things that are unexpected and grab the most informative stuff as well.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
That if you're in a state of focus, do you enhance the release of dopamine?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. I, well, I don't know. I wish I could give you an answer and say, I don't know. And it would be really hard to disentangle the chicken and the egg, right? Because if you're measuring dopamine activity, you'd have to, well, okay, so here's what I can say. is that I think that we often think of, you know, we think of like, let's say an emotion, right? Or any other mental state.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And we think of it like it just happens. But in fact, there's a timescale to these things, right? So it's like, there is a basic response that you get when somebody points a gun at you. But then there's an interpretation that you have that can take that threat response and make it into something more. And then you're like really jacking up your neuroadrenergic activity, right?
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Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. But it's like – I mean, well, in that case, it could be a catastrophe.
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Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, but that can still be scary, right? Sure. And this is where I think it's like this, we talked about this before, this appraisal is very important. In the case of focus, it's a little bit different, but just to make this very concrete, the prefrontal cortex has top-down inputs to many of the neuromodulatory systems.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So on average, people tend to think of the neuromodulatory systems like dopamine and norepinephrine as being very bottom-up. They just send signals everywhere and set the brain into focus or not focus or whatever. But the prefrontal cortex has some – anatomically at least some capability of regulating those systems both directly and indirectly.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so that does I think speak to this idea that if you have a very strong goal focus, you can in fact regulate the dopamine system. I think it's a reasonable – And norepinephrine too, noradrenergic system. So I think it's a reasonable thing. And I bet you Amy Arnston has done some related work on this topic.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
This is just starting to be a thing, but the effect sizes, for instance, for hearing aids are really strong, both in reducing AD risk, I believe, and in Alzheimer's risk, and in just good cognitive aging and keeping your memory as you get older.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I've got to have you teach this to me sometime.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, actually, OK, so speaking of things I did to preserve my brain health, I'm playing in a band now and we're pretty damn loud. And so I got I went to an audiologist and I got custom earplugs.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Oh, yeah, yeah. But I think these custom ones will be more effective at both preserving the spectrum of all the frequencies.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
No, but they're related because if you can't hear your frequencies, you might end up turning up and you get this paradoxical thing. Sure. Too much information, I know. But basically, that is, yeah.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So there is this issue with, in fact, actually, there's an article that Shirzai sent me in The Lancet that one of their public health recommendations is to get into a preventative mode for preventing Alzheimer's disease. And one of the things they say is screen for hearing and give people hearing aids and make people use them if they encourage people to use them.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Vision is starting to be a big one. People who are older get cataracts, get it treated, you know. A lot of this preventative healthcare, which our system is not really equipped for it, but it can really save so much money. It can save so much emotional pain for so many people. It's really amazing. Another one I mentioned briefly is oral hygiene.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Gum disease, it turns out, increases your risk for, I believe it's Alzheimer's and also for cognitive brain health in general.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah. I mean, I don't know the detailed mechanisms, but I think that makes sense. And there's this vague notion of cognitive reserve, which is basically some people seem to be quite immune to the effects of cognitive aging, and some people seem to be very protected against Alzheimer's disease. So what is it?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
One of the things that seems to come up as far as depleting cognitive reserve or putting it at a higher risk seems to be inflammation, right, neuroinflammation. And so Kim McAllister, as you know, is doing work on this topic of neuroimmune interactions. Mm-hmm. Basically, the immune system expresses itself in the brain. You get microglia activation that can cause these inflammatory responses.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And there's reasonable evidence suggests that it's interacting with tau and amyloid and this kind of cascade of stuff that happens in Alzheimer's disease, right? And one of the things that we're learning now, and we don't know nearly enough, but the data out there is quite scary, in fact, is long COVID is associated with significant cognitive effects.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, so they report a subjective brain fog and you can see this, you can measure this as a significant cognitive deficit that they're experiencing, right? And we've seen in the past like HIV was, there was actually a whole variety of dementia that was associated with HIV from the viral transmission.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
We can – like you can see with multiple sclerosis where you have like autoimmune responses in the brain affect mental function dramatically. We're seeing more and more evidence of this. So this is again another one of those things. It's like people go, oh, COVID. I don't care about it, blah, blah, blah.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I mean this is a health thing that can really affect people and it can – I don't think anybody – it's not a political issue to get brain fog. It just sucks, right? Nobody wants this. So I think that there's a lot we're learning about viruses and bacteria. One of the cool things I was talking about before we started recording is I was at a conference.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I met the coolest guy, and I'm blanking on his name, but I'll send it to you after. But he did this great study, and he was studying the effects of nutrition on brain health and memory, especially cognition. So I said, what's the most interesting finding that you've gotten? I love to ask people this because I'm curious and it stimulates my curiosity and I usually get a good answer.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So he told me he did this study where he has these rats and he gives them sugary water during the day about the equivalent, he said, to a can of Coke a day. So they're getting this sugar. When they reach adulthood, you know, these teenage rats, they reach adulthood and they have memory problems and they have hippocampal atrophy.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So you go, okay, well, the hippocampus is affected, memory is affected, sugar, blah, blah, blah, no problem. So then what he does is he takes the gut bacteria from the sugar animals and puts it in an animal that doesn't get this diet. And he finds the same kind of pathology and the same kind of memory deficit in these animals.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So there's something about that process of like the gut-brain interaction that also seems to be playing a part in ways that I don't understand. I think they're still figuring it out. But again, this really shows this tight neuroimmune link. We're seeing this now with pollution. Air pollution is a big factor.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So even if people don't believe in global warming, there's nothing good about being in a place with a lot of smoke in the air, you know. It definitely can and this is one of the risk factors that is noted in the Lancet report for Alzheimer's disease.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
One of my colleagues Pam Line is doing research on this at UC Davis showing that you get like she actually takes real pollution from the Caldecott tunnel which connects Oakland and Walnut Creek and finds that rats exposed to this pollution. damage. So there's so many of these environmental factors that can trigger the inflammatory response. We talked about blood sugar.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Blood sugar also seems to be related to these issues. And diabetes is like so bad in so many ways. It's associated with those white matter hyperintensities that we talked about. And so that's bad. We've done some research on that. But it also affects – it can cause little – if you get severe diabetic ketoacidosis, you can actually have hippocampal damage from that directly.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And it also dramatically increases Alzheimer's risk. We have an epidemic of diabetes right now.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, a lot of your sense of where you are comes from episodic memory. Now, there's a school of thought that says that episodic memory, which is your ability to remember past events, comes from your ability to understand where you are. And we have some interesting data from sea lions, actually, that speaks to this issue.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
There are now some drugs that are, I think they're targeting amyloid that are producing some modest effects in stalling the progression of the disease. See, the problem with Alzheimer's, as you know, is once you lose neurons, you're not getting them back, right? And it's like, yeah, there's neurogenesis and you can run around, but it's not much. If you're depending on that, you're hosed.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But getting back to the exercise thing, It's neuroprotective. And so like let's say with a drug, right? I mean everybody wants a drug. If I told you I give you this drug, you're 60 years old, and it's going to have some terrible side effects. You're going to get diarrhea, nausea, all this stuff. But it will reduce your risk of Alzheimer's by 40%. A lot of people would be motivated to take it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Now I tell you, okay, well, here's a lifestyle intervention that's going to involve what Sarah Madden calls downstates. We can actually get into that and memory reactivation during downstates, but involves sleep, diet, exercise, social stimulation, right? And these things, by the way, also reinforce each other. Right. Having better sleep makes it easier to exercise.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Having exercise makes it better to sleep. All of these improve mood, right? So these will improve your mental function, your mood, as well as your mental function relatively soon and reduce your risk by at least 40%, if not more. Wow.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
If you go to – I can send you this Lancet article, but it's like the amount – the proportion of variance, meaning the degree of risk that you can reduce with fully preventable or fully in our control lifestyle issues is huge. It's as big or bigger than the genetics.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Traumatic brain injury is another one of the big risk factors.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Sea lions, yeah.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, it's not fully understood, but I'll give you my best guess that's science-based and not just my wildly speculating completely. But basically, one of the early findings that gave you a sense about what deja vu is, is Hewlings-Jackson, who's this great neurologist who did pioneering work in behavioral neurology.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
We'll get back to the sea lions. I would argue that to remember where you are when you first get up, you have to engage in an active episodic memory retrieval. That is, you have to figure out, well, how did I get here? And that takes a moment. Orienting yourself takes a moment. And that – because it's a little bit of a controlled memory search, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
observed that many patients who get epilepsy would have this aura, it's this mental sensations right before a seizure, where they would get an intense feeling of deja vu. It doesn't happen in everyone, but a certain number. And this is associated with temporal lobe epilepsy. And the hippocampus, as you know, is in the temporal lobe.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But there's also these areas around it that are super important for memory, including the amygdala, but also really the perironal cortex is a key, key player in this. And so the... So then you have Wilder Penfield and other people who started to do these surgeries for epilepsy and they said, well, I want to make sure I'm not taking out good brain, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So Penfield wasn't responsible for HM and that was like kind of an irresponsible surgery.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. And so, in fact, he had this dense, dense amnesia, right? And actually one of the little known things even in memory research is he actually lost – he had what's called a temporal lobectomy where they just hack off the front part of the temporal lobe. It might have been cauterized. I can't remember the – I think he cauterized it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But anyway, they do that temporal lobectomy and he actually had the posterior one-third of his hippocampus. But he had lost his perirhinal cortex bilaterally. And that turned out to be Betsy Murray at NIH later and other people turned out to be a huge thing. So one of the reasons I think that he became so densely amnestic is that it was bilateral.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So if you think about the brain, like you have a side of the brain that's causing a seizure, so you kind of got a spare tire on the other side where it's like that other healthy tissue on the other side can sometimes pick up the slack. But if you take out both hemispheres, now you're in really bad shape. So... Scoville did that.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
He actually did it for people who are... HM had epilepsy and it was a legit operation in that sense, but he did it for people who had, I think, like psychosis too, depression. I mean, back then they just did all kinds of crazy stuff. But Penfield was like, no, I want to make sure I take out only the tissue that needs to go. So what do you do?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
You stimulate different parts of the brain and you see, does it produce anything other than a seizure? And if so, that's not an area you want to remove. And so you would go into the anterior temporal lobes and stimulate, and people would have – sometimes they would have an intense real memory.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But sometimes they would have this intense sense of deja vu where it's like they feel this – I feel like I've lived out this whole thing that's happening right now. I've lived it before. When you know that's not true, right? So what is this? Well –
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
A number of people, my lab was heavily involved with this, and Andy Annalenis at UC Davis was, you know, really central to a lot of the stuff, found that the perirhinal cortex, which is this area, as I said, it's a big player with the hippocampus, seems to be very critical for this general sense of familiarity that we have.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's not something that's in front of you that reminds you of where you are initially. And you're also in this little bit of a fog when you wake up. I don't know enough about sleep to say, but I would suspect that people probably are in some kind of a – stage one-ish or just high alpha, these brain waves that are like very much associated with kind of grogginess as you're getting up.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so, you know, I use in the book an example of like, if I say, have you eaten a rambutan before? Now, you being a worldly guy might, have you ever eaten a rambutan?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Okay. So how quick was it that you were able to say no, that you were able to think about it and go, I've never eaten rambutan?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Okay. So you didn't have to search your entire memory for whether or not you've eaten rambutan. You know because it's so unfamiliar, right? Correct. Things that are highly familiar, like maybe I'll ask, have you eaten a banana before or grapes before? You can say yes. And partly, you don't even have to remember any instance. It just feels right. Those are very familiar things to you.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Have you ever seen a grape before? Yes, of course you have, right? Apple, very familiar to people. So we just have that general fluency. And you can look at this like you go into the grocery store and you see someone and you're like, I know I've seen this person before. Where have I seen them before?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And then you leave and eventually you're like, oh, well, that was somebody who I met at this conference or something like that. But you weren't expecting them at this context and no episodic memory was triggered. But there was something about their features that felt very fluent and natural to you and triggered that sense of familiarity.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And that seems to be processed, and you can see brain activity associated with that in the perirhinal cortex. And people with damage to the perirhinal cortex seem to not differentiate between the rambutan and the banana. It's all kind of unfamiliar to them. They might remember, I've eaten a banana, but they don't necessarily have that sense of familiarity.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And Rebecca Burwell at Brown University did the coolest experiment that doesn't nearly get... You know how in science you get these unsung hero experiments? Well, this was one of them where she stimulated in rats the perirhinal cortex at this frequency called the beta frequency, which is kind of a relatively low frequency oscillation, and basically put two objects in front of the animal.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so, like, typically if there's a new object, the animal will spend more time, like, exploring it, right? Yeah. And depending on how she timed the stimulation, she could make the animal think that a familiar object was novel. She stimulates at a different frequency. I think it was gamma. And the animal now thinks – or actually it was like – yeah.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So she thinks now the animal thinks that a familiar thing is novel. With beta, it was that it thought a novel thing was familiar. Wow. So could literally use this stimulation to change the way the animal is interacting with and presumably a memory-driven way with this object, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Maybe, yeah. And so Anne Cleary, just to close the loop here, who's a great researcher at Colorado State, developed this beautiful paradigm where what she does is she said, OK, well, does that relate to déjà vu? Right. Well, let's see. So what she did was use virtual reality. And so in virtual reality, you can create these environments and put objects in particular places.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so she creates these virtual environments where there are particular objects in particular places. And let's say one's a museum, right? So a person can go through passively and watch a movie, or they actively navigate through these spaces. And then what she does is she has them go through, let's say, a video arcade. But unbeknownst to the subject,
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
The objects that are in the room are in exactly the same positions as the objects in the museum. But it's a video arcade, so it looks different. But the room shape, the spatial layout, you know, everything is identical. It's got a different skin on it, so to speak, for video gamers.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Neuromodulators are probably super low.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So what happens is people are much more likely, very likely to produce a deja vu sensation when they're in these places, these virtual environments that look very much like where they've been, but they're mismatching in some critical way. So it's like you've got enough to trigger the strong sense of familiarity, but the mismatch is suppressing recollection.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so that seems to be a crucial part of why you get this uncanny feeling of remembering things. is the strong familiarity you get. And by the way, I've watched these movies, and I cannot for the life of me see that the museum is the same as the arcade. It just feels so different cognitively.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But, you know, I can imagine being like, if I really did it immersively, having that sense of familiarity. So you're really pitting these things in opposition to each other. And so what likely happens with déjà vu is something – uncanny that triggers a little bit of memory retrieval or a strong fluency, but then there's a mismatch that suppresses it and prevents a context from coming up.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah, exactly. And so that's going to lead you to really be slow in doing that memory retrieval that you need to orient yourself. So like in the clinic, if you want to ask, if you want to understand whether someone has a memory disorder, one of the simplest things is to ask them what day of the week is it? What month is it?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Oh yeah, we got to talk about that.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Who's the president? Yeah. Right now that's a loaded question.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, you could blow out the serotonergic system with too much of it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, I mean, this is abuse we're talking about.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, rumination basically.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Again, you know, serotonin is like a neuromodulator. It enhances plasticity. And what I mean by that is that if you have like a transient learning event, you will get a change in the connections between neurons that were active during that event. And super interesting work right now going on in behavioral timescale plasticity and all this stuff.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So it's not just solves the wire together, fire together. It's more interesting, actually. Or fire together, wire together. It's more interesting. But... Those changes can often be transient.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And what people, so like Eric Kandel, for instance, one who studied serotonin in particular and emphasized this, but basically many neuromodulators, if you give a little bath, bathe these neurons in serotonin or other neuromodulators, you stabilize that plasticity. And that allows increases in receptor density between these neurons that allow them to communicate more effectively.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Now you can get weakening and LTD too. We won't get into that. But serotonin definitely promotes plasticity, right? And so one of the things I talk about in my book is that memories are – I mean we all have plasticity. As I said, retrieving a memory can allow us to change the memory in certain ways.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And it can change – when you get into the details of it, it becomes complicated in interesting ways. But – The short version is you can change it. We get a small part of what happened when we remember. But there's that feeling of the context. There's that emotional response that we have that's both a kind of a basic raw motivational, my heart's racing or something like that.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
That's why people often say, well, emotional memories are stored in the body. Well, it's just part of the memory. It's a retrieval cue, so to speak. And it can also be part of the retrieved experience. But you have all of these factors going on that are part of this emotional memory. And then you have a story that you create, a narrative that you use to make sense of it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And that affects all these physiological systems too, right? So... Every time I talk in the book about an example of how group therapy is so powerful as a means of memory updating and social interactions, where it's like people can change the narrative.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
They say, well, I gave you this narrative about how I'm loud, and you told me, well, I remember hanging out with you, and you weren't loud then, and you're not loud now. And so now I can update these memories maybe.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, exactly. I could reframe it, right? And these framing effects are huge. So in theory, people can take an experience that was traumatic, and many people do, and say, this made me who I am, and I'm happy with who I am now, even though it's a horrible thing. I'm stronger for it, or I'm a survivor, or I couldn't have done anything about it, and it's not my fault.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Or you can have these narratives of shame and so forth and guilt and anger and so forth. I'm not judging anybody's reaction to trauma. But what I am saying is that's part of the emotional response. It's part of the memory that people construct.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
The problem is that with traumatic memories, when they do stick, it's hard to change because there's so much plasticity driven by the neuromodulators during that event. With PTSD, I mean, we could talk about that as a whole other thing, but let's just take traumatic memories. It's so intense, and the amygdala response drives the physiology in many cases of that arousal.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
which makes you feel like this immediacy of it, right? And it affects sleep and nightmares also. But anyway, stay out of PTSD for a moment because that's a whole other thing. But those memories are very resistant because of that intensity. And often the more we retrieve them, we re-traumatize ourself.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So reframing in a cognitive therapy sense is very difficult because they feel this and their brain is telling them I'm under threat or I'm ashamed because they've reinforced this narrative so many times. And you can work through the logic, but sometimes you need to create some big prediction error to generate some error-driven learning, which is something we can talk about, or
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
you need some kind of help. So if you're driving neuromodulatory systems, that theoretically could give you a broader window of plasticity. In fact, actually, we're trying Prozac on my dog. And one of the things that I've seen- Why?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
She's very anxious.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And it's to the point where she'll not exercise, even though she's a very active dog. She'll stop on a walk if she hears a garbage truck anywhere. And so it's a very low dose. And I'm not necessarily saying go drug your dogs.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But I'm just saying that the story that I've heard is that you get this period of plasticity where you can kind of rewrite some of these behavioral patterns and make them more open to training and so forth. And so it doesn't even have to be a permanent thing, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And I think a lot of these things like you're talking about, learned helplessness studies, probably transient effects of not being on it for years or something. Mm-hmm. But it's not very effective in terms of SSRIs. But psilocybin and psychedelics have shown a lot of promise as being bigger effects, right? And these produce massive plasticity.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
There's two things I think that are really interesting about it. By the way, Davis, I will just say I'm biased, but it's one of the – top three places in the world for learning and memory research. So next door neighbor, David Olson, it turns out, is studying psychedelic effects on plasticity.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And, you know, so he really emphasizes that there's these massive neurotrophic factors, BDNF, like all these factors that are going on that are promoting plasticity. And, you know, for people who've taken them, that's what they report is that there's this period of integration afterwards where your brain's just like... you know, you could feel it. Everything.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, here's what I'll say. It's a really interesting and complex question. You always talk to a scientist, you get that it's complicated. But I'll give you as simple of a thing as I can, which is, so if you look at patients with amnesia, so they have a memory disorder where they can't form new memories, they have a sense of who they are, as you mentioned, right?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
That's right. It opens up like significant opportunities for reshaping. But the second part of it, which maybe I think is really interesting, is there is also a dissociative element of these drugs. So ketamine isn't a psychedelic, but I think there are some interesting plasticity effects and definitely produces this dissociative element too.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But with psychedelics, there's often a major perspective shift. Perspective is hugely important for memory because a lot of our sense of the emotional impact of our memory is based on a perspective that we adopt when we remember. Research has shown that you can take the same encoding event Meaning like I tell you a story – let's just take a very simple thing.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Very – I give you a story and it's like I tell you now viewed from the perspective of someone else and you're trying to remember it. You can remember things that you didn't remember the first time around. Changing your perspective can literally change what you remember. It can also change the narrative that you produce.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
So now let's say you pull up this traumatic memory, but you're viewing it from the outside and you're feeling your heart's racing, your eyes are dilating, these crazy effects from psychedelic, but you're seeing it and it's not you. There's some deeper self you're feeling, whether it's true or not.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's – I mean there's so much that we don't know and I think it's – and I will say that some of the psychedelic stuff is overhyped and there's not – some of the science is quite bad in that field right now.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It's not like they don't know who they are. And I mean like they know their names, they know their biographies and so forth. But what happens is at the time, let's say if you had gone swimming and you nearly drowned, you had a hypoxia incident or a cardiac arrest or you had like a traumatic brain injury, severe memory deficit, right? Your sense of self doesn't update. It gets kind of stuck.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah. Yeah. I do think that some of the concerns they had in the FDA I take issue with. But what I will say is that – You have a drug that dramatically increases plasticity, but it changes dramatically the mental context that you have when you pull up the memory. So you have a real opportunity for memory updating. Now there's a phenomenon in the animal literature called reconsolidation,
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
where essentially the act of retrieving a memory opens it up to requiring some kinds of neuromodulators again to really promote resealing of the memory, so to speak. But it can also, if you interrupt it, you can erase the memories. And theoretically, if you can do that, you could also change the memories pretty significantly. So if I can vividly access some neural population that's
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
normally gives me this physiological response. It sets off this train of thoughts, and it's associated with this physical and mental context. And I can access those neurons, but dramatically reshape the context and dramatically reshape the narrative. I've created the opportunity for massive change. And I don't know if that's true, but it sure makes sense to me that that's the case.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Now, having said that, If you and me share our traumatic elements of our childhood, I'm sure we can go out for drinks and do this for quite a few hours, right? That in and of itself will also produce some change in our memories. It's very powerful. And I saw this in the clinic where I was doing group therapy with Vietnam vets. And I'm like... I'm a total fraud.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I'm like, I don't know, 27 years old, 28 years old. And I'm like in with these like, you know, Vietnam vets in their 50s who've really seen stuff, you know, and they live in combat zones now in Chicago. And what I realized was everyone was telling their story.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But they're hearing reflections of their story from me, but also from other members of the group who they can relate to that are different from their narrative. And now all of a sudden what happens is the memory is no longer theirs. It's a collective memory that's shared by all these people because the memory now incorporates elements of their reactions as well.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
It allows people to remember it in a new context, right? And I mean, and we can just take a much more watered down version of this where how many times have you had a terrible experience and it became a great story? I basically say that there's no point in having a bad experience in life if you don't get a great story out of it, right? So I talk in the book about a near-death experience.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I had paddle boarding and everything about this was stupid. It's like the degree – I could send you pictures of it and you'd be like, oh my god, what was he thinking?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah, exactly, exactly.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah. Well, so, I mean, to be clear, it's like I felt horrible during that experience, and it was one of the most immediately fear-inducing experiences I've had. But later, me and Randy O'Reilly of computational neuroscience were friends. We both did this stupid thing together. We would tell the story, tag team it, and we told it to students and friends and so forth.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And it just became funny. And so each time we told it, it just became kind of funnier and funnier, and you start to embellish things and so forth. And so that change of perspective was really drawn out by sharing and seeing people laugh and seeing people like, what were you thinking? You're such a smart person and you did this. And it becomes part of the narrative.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And keep in mind, there are people who do this, that they say like, I've had a really traumatic experience, but I've learned from it. I've had a horrible, emotionally abusive relationship, but I've learned from it, right? And I don't mean to trivialize anybody's experience who didn't have that thing and they're just traumatized by it and they carry it with them.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so there is kind of a sense of looking and not – expecting yourself to be as old as you used to be, as you are, because you're stuck in your sense of who you were. And I do think, I talked to my good friend Rick Robbins at Davis as a personality psychologist, and he studies the development of personality. And it does develop. It kind of stabilizes in these adolescent years.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
But what I am saying is, is that the memory, so to speak, I think in neuroscience right now, there's a big hot topic about engrams as if a bunch of neurons is the memory. But every time we have a memory, we're painting a new picture. We're creating a new novel.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah. And it's all about like because you can re-traumatize yourself. And this is also why rumination is so bad in depression is because you recall a negative memory and that gets you in a negative mood because you pull up the context. And then that makes it easier to recall more negative memories.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And then every time you recall them, now they're getting more power because they're associated with these negative moods.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Oh, yeah. Yeah. I mean look at like – so if you take something like reminiscence or nostalgia. So the original term nostalgia, I credit Philippe de Burgard for – he's a philosopher, neuroscientist. He told me that nostalgia used to be a term for a disease that was coined by a Swiss physician. Mm-hmm.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And he used it to talk about a kind of post-traumatic experience that soldiers had where they would get so wistful about their home that it just made them miserable in the places that they were at.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah, yeah, exactly.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yeah, yeah. And so it can – the research shows it can have very positive effects on mental health, right? And it can have positive effects on mental health if you use that as a way of saying, hey, this is just a great thing that's happened. I'm grateful for that. But it can become toxic if you're like, my life used to be so great and now it's terrible.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Even if it's positive reminiscence, if you come into it with the wrong attributions, it can become negative and toxic and it can contaminate your present, right? I mean, the past has got good and it's got bad in it, just like the present. It's got good and it's got bad in it. And it's really all about what are the narratives you're constructing for it in many ways.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And that plays a big part in the dynamic, malleable, constantly shape-shifting nature of memory.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yep, actually I have a couple bands now, thankfully.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, so Pavlov's Dogs, I'll say, versus like a band of neuroscientists and psychologists, neuroscientists who met actually, most of us met at a memory meeting actually. And so we get together at conferences and we'll rent out a club and we'll play basically – Brad calls it skinny tie music.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Covers. That one is a cover band.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
OK. And so we'll play like the Ramones, the Clash, Gang of Four. Great. It's a lot of – we added Blondie and –
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And that's actually also interestingly related to memory. But it does change. People do change in really interesting ways. So one thing is that people grow more optimistic on average as they get older. Is that right? Yeah. Yeah, that's true. So Laura Karstensen, your colleague at Stanford, actually has done some really cool work on that topic.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I play guitar and I also do vocals.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Yes or yeah. Reluctant because sometimes it's talking or being off key, but yeah.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I think we have some recordings on YouTube. And if you look on our Facebook page, maybe our Instagram too, we have live recordings.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
I think it's the 7th. Is it a month? It's the Monday.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Sometimes, and that's when I suck. Actually, you know, one hack that I came up with, because it's like with the cover band, we practice like we cram. It's the worst thing. It's not space learning. It's like we go through the songs and we keep adding and taking away songs. But it's like we'll cram for like, I don't know, about eight hours of practices over three days or something.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so for me, it's like a constant memory thing because my brain doesn't want to play covers. It wants to play the songs that I've written. And so there's always this memory thing. And then I get nervous. I get really nervous. And so I move a lot. And then I'll see friends. And that kills me because then I start thinking, what are they thinking?
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And so I started – last show I did with Pavlov's Dogs, I wore sunglasses in it. was great. Because then I wasn't attuned to them. And it just goes back to what we're talking about kind of with the camera and stuff. I was feeling it. And I was thinking. I was in the flow, in the zone, and feeling it and doing it and not thinking about it.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
And there's a whole interesting literature, Choking Under Pressure, that actually relates to this idea of sometimes having too much cognitive control going on is really bad. When you're under stress and if you know something fairly well, you're going to be better off if you just go into an automatic state.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Oh, I would love to. Thank you, Andrew. It's just been great to be here.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Well, you know, so I think that's overdone a little bit. I think you're right. You know, you definitely see less dopamine activity, for instance, as people get older. But what I'll say is that people have gobs – if you have a healthy aging person, they have gobs of neuroplasticity. But often what happens is, yeah, you get stuck in your ways, and that could be related to a few things.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
One is that you get changes in the prefrontal cortex, and that leads you to be less cognitively flexible. It can be also because people just build up so much prior knowledge about the world that it just becomes kind of ingrained that this is the way it is, and it's harder to be surprised. I mean, you kind of see this with old scientists, right? They go like, nothing's new.
Huberman Lab
Dr. Charan Ranganath: How to Improve Memory & Focus Using Science Protocols
Everything's been discovered in 1960, and nothing new has happened since then.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I would say superficially, not that hard, but then in a deeper level, very, very hard because we don't understand episodic memory, right? So one of the ideas I talk about in the book is one of the oldest kind of dilemmas in computational neuroscience is what Steve Grossberg called the stability plasticity dilemma, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
When do you say something is new and overwrite your preexisting knowledge versus going with what you had before and making incremental changes? And so- You know, part of the problem with going through like massive, you know, I mean, part of the problem of things like if you're trying to design an LLM or something like that is especially for English, there's so many exceptions to the rules, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so if you want to rapidly learn the exceptions, you're going to lose the rules. And if you want to keep the rules, you have a harder time learning the exception. And so David Marr is one of the early pioneers in computational neuroscience.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then Jay McClelland and my colleague Randy O'Reilly, some other people like Neil Cohen, all these people started to come up with the idea that maybe that's part of what we need and what the human brain is doing is we have this kind of a, actually a fairly dumb system, which just says this happened once at this point in time. which we call episodic memory, so to speak.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then we have this knowledge that we've accumulated from our experiences as semantic memory. So now when we want to, we encounter a situation that's surprising and violates all our previous expectations, what happens is that now we can form an episodic memory here.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And the next time we're in a similar situation, boom, we can supplement our knowledge with this information from episodic memory and reason about what the right thing to do is, right? It gives us this enormous amount of flexibility to stop on a dime and change without having to erase everything we've already learned.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
That solution is incredibly powerful because it gives you the ability to learn from so much less information really, and it gives you that flexibility. One of the things I think that makes humans great is having both episodic and semantic memory. Now, can you build something like that?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, computational neuroscience people would say, well, yeah, you just record a moment and you just get it and you're done, right? But when do you record that moment? How much do you record? What's the information you prioritize and what's the information you don't? These are the hard questions. When do you use episodic memory? When do you just throw it away?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And these are the hard questions we're still trying to figure out in people. And then you start to think about all these mechanisms that we have in the brain for figuring out some of these things. And it's not just one, but it's many of them that are interacting with each other.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I really try to do now vacations to interesting places as much as possible with my family, because like, those are the things that you remember, right? So I really do think about what's going to be like something that's memorable and then just do it even if it's a pain in the ass because the experiencing self will suffer for that.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then you just take not only the episodic and the semantic, but then you start to take the motivational survival things, right? It's just like the fight or flight responses that we associate with particular things or the kind of like reward motivation that we associate with certain things, so forth. And those things are absent from AIA. I frankly don't know if we want it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I don't necessarily want a self-motivated LLM, right? And then there's the problem of how do you even build the motivations that should guide a proper reinforcement learning kind of thing, for instance. Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
A friend of mine, Sam Gershman, I might be missing the quote exactly, but he basically said, you know, if I wanted to train like a typical AI model to make me as much money as possible, first thing I might do is sell my house. So it's not even just about having one goal or one objective, but just having all these competing goals and objectives, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then things start to get really complicated.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, yeah. I mean, well, even if we want to go super simple, right? Like Tyler Bonin, who's a postdoc who's collaborating with me, he actually studied a lot of computer vision at Stanford. And so one of the things he was interested in is some people who have brain damage in areas of the brain that were thought to be important for memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But they also seem to have some perception problems with particular kinds of object perception. And this is super controversial. Some people found this effect, some didn't. And he went back to computer vision and he said, let's take the best state-of-the-art computer vision models and let's give them the same kinds of perception tests that we were giving to these people. Mm-hmm.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then he would find the images where the computer vision models would just struggle, and you would find that they just didn't do well. Even if you add more parameters, you add more layers, on and on and on, it doesn't help, right? The architecture didn't matter, it was just there, the problem.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then he found those were the exact ones where these humans with particular damage to this area called the perirhinal cortex, that was where they were struggling. So somehow this brain area was important for being able to do these things that were adversarial to these computer vision models. So then he found that it only happened if people had enough time they could make those discriminations.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But without enough time, if they just get a glance, they're just like the computer vision models. So then what he started to say was, well, maybe let's look at people's eyes, right? So a computer vision model sees every pixel all at once, right? It's not, you know, and we don't, we never see every pixel all at once. Even if I'm looking at a screen with pixels, I'm not seeing every pixel at once.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But the remembering self will be like, yes, I'm so glad I did that.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I'm grabbing little points on the screen by moving my eyes around and getting a very high resolution picture of what I'm focusing on and kind of a lower resolution information about everything else.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But I'm not necessarily choosing, but I'm directing that exploration and allowing people to move their eyes and integrate that information gave them something that the computer vision models weren't able to do. So somehow integrating information across time and getting less information at each step gave you more out of the process.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, at the same time, people are terrible at detecting changes that can happen in the environment if they're not attending in the right way, if their predictive model is too strong. So you have these weird things where the machines can do better than the people. It's not that it's like, so this is the thing is people go, oh, the machines can do this stuff that's just like humans.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's like, well, the machines make different kinds of mistakes than the people do. And I will never be convinced unless I that, you know, we've replicated human. I don't even like the term intelligence because it is a stupid concept. But it's like I don't think we've replicated human intelligence unless I know that the simulator is making exactly the same kinds of mistakes that people do.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, I mean, I think it's one of these things where if you have, like, people who you've gone through, since you said it, I'll just say, since you've gone through shit with someone, and it's like, that's a bonding experience often, you know? I mean, that can really bring you together. I like to say it's like there's no point in suffering unless you get a story out of it. So...
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Because people make characteristic mistakes. They have characteristic biases. They have characteristic like, you know. heuristics that we use, and those, I have yet to see evidence that ChatGPT will do that.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, it's interesting for me because when I was a child, I was actually told my school, I don't know if it came from a school psychologist, they did do some testing on me, I know, for like IQ and stuff like that. Or if it just came from teachers who hated me, but they told my parents that I had ADHD. And so this was, of course, in the 70s. So basically, they said like,
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
He has poor motor control, and he's got ADHD, and there were social issues. So I could have been put a year ahead in school, but then they said, oh, but he doesn't have the social capabilities. Right. So I still ended up being like, you know, an outcast even in my own grade.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But then like, so then my parents said, okay, well, they got me on a diet free of artificial colors and flavors because that was the thing that people talked about back then. So I'm interested in this topic because I've come to appreciate now that I have many of the characteristics, if not, you know, full blown. It's like, I'm definitely time blindness, rejection sensitive, you
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
name it they talk about it it's like impulsive behavior i can tell you about all sorts of fights i've gotten into in the past just you name it um uh but yeah so adhd is fascinating though because right now we're seeing like more and more diagnosis of it and i don't know what to say about that
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I don't know how much of that is based on inappropriate expectations, especially for children, and how much of that is based on true maladaptive kinds of tendencies. But what we do know is this, is that ADHD is associated with differences in prefrontal function, so that attention can be both more—you're more distractible.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You have a harder time focusing your attention on what's relevant, and so you shift too easily. But then once you get on something that you're interested in, you can get stuck. And so the attention is this beautiful balance of being able to focus when you need to focus and shift when you need to shift. And so it's that flexibility plus stability again.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And that balance seems to be disrupted in ADHD. And so as a result, memory tends to be poor in ADHD. But it's not necessarily because there's a traditional memory problem, but it's more because of this attentional issue, right? And so people with ADHD often will have great memory for the things that they're interested in and just no memory for the things that they're not interested in.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
In the book, I talk about the power of the way we communicate with others and how that shapes our memories. And so I had this near-death experience, at least that's how I remember it, on this paddleboard where just everything that could have gone wrong did go wrong almost immediately.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's not like being a doctor or something where you have to be much more responsible and focused. You can just freely follow your curiosity, which is just great. But what I'd say is that I'm learning now about... so many things like about how to structure my activities more and basically say, okay, if I'm going to be, email is like the big one that kills me right now.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I'm just constantly like shifting between email and my activities. And what happens is, is that I don't actually get the email. I just look at my email and I get stressed because I'm like, oh, I have to think about this. Let me get back to it. And I go back to something else. And so I've just got fragmentary memories of everything, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So what I'm trying to do is set aside a time where I'm like, this is my email time. This is my writing time. This is my goofing off time. And so blocking these things off, you give yourself the goofing off time. Sometimes I do that. And sometimes I have to be flexible and go like, okay, I'm definitely not focusing. I'm going to give myself the downtime. And it's an investment.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's not like wasting time. It's an investment in my attention later on. Mm-hmm.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, I mean, you probably see this, I imagine, in AI conferences, but definitely in neuroscience conferences. It's now the norm that people have their laptops out during talks. And, you know, conceivably they're writing, you know, they're writing notes. But in fact, what often happens if you look at people, we can speak from a little bit of
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
personal experience is you're checking email and you're like, or I'm working on my own talk, but often it's like you're doing things that are not paying attention. And I have this illusion, well, I'm paying attention and then I'm going back. And then what happens is I don't remember anything from that day. It just kind of vanished because what happens is
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So many mistakes were made and ended up at some point just basically away from my board, pinned in a current in this corner, not a super good swimmer. And my friend who came with me, Randy, who's a computational neuroscientist and He had just been pushed down past me and so he couldn't even see me. And I'm just like, if I die here, you know, I mean, no one's around. It's like you just die alone.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I'm creating all these artificial event boundaries. I'm losing all this executive function. Every time I switch, I'm getting like a few seconds slower and I'm catching up mentally to what's happening. And so instead of being in a model where you're meaningfully integrating everything and predicting and generating this kind of like rich model, I'm just catching up, you know?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so, yeah, there's great research by Melina Unkefer and Anthony Wagner on multitasking that people can look up that talks about just how bad it is for memory. And, you know, it's becoming worse and worse of a problem.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, so I started playing music just when I was doing trumpet in school for a school band, and I would just read music and play, and it was pretty decent at it. Not great, but it was decent.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
yeah so basically in high school yeah so i kind of was a late bloomer to music but just kind of mtv grew up with me i grew up with mtv and so then you started seeing all this stuff and then uh i got into metal was kind of like my early genre and i always reacted to just things that were loud and had a beat like uh i mean adhd right it's like uh Like, you know, everything from Sgt.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Pepper's by the Beatles to, like, Led Zeppelin II my dad had. My parents had both those albums, so I listened to them a lot. And then, like, The Police, Ghost in the Machine. But then I got into metal, Def Leppard and, you know, ACDC, Metallica, went way down the rabbit hole of speed metal. Mm-hmm. And that time was kind of like, oh, why don't I play guitar? I can do this.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I had friends who were doing that. And I just never got it. I took lessons and stuff like that. But it was different because when I was doing trumpet, I was reading sheet music.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And this was like, I was learning by looking, there's a thing called tablature, you know this, where it's like you see a drawing of the fretboard with numbers and that's where you're supposed to put your, it's kind of like paint by numbers, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
and so um i learned it in a completely different way but i was still terrible at it and i didn't get it it's actually taken me a long time to understand exactly what the issue was but it wasn't until i really got into punk and i saw bands like i saw sonic youth i remember especially and it just blew my mind because they violated the rules of what i thought music was supposed to be i was like
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
this doesn't sound right. These are not power chords. And this isn't just have like a shouty verse and then a chorus part. It's not going, but this is just like weird. And then it occurred to me, you don't have to write music, uh, the way people tell you it's supposed to sound. That just opened up everything for me.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I was playing in a band and I was struggling with writing music because I would try to write whatever was popular at the time or whatever sounded like other bands that I was listening to. Somehow I morphed into just grabbing a guitar and just doing stuff. And I realized a part of my problem with doing music before was I didn't enjoy trying to play stuff that other people played.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I just enjoyed music just dripping out of me and just, you know, spilling out and just doing stuff. And so then I started to say, well, what if I don't play a chord? What if I just play like notes that shouldn't go together and just mess around with stuff? And I said, well, what if I don't do four beats going, nah, nah, nah, nah, one, two, three, four, one, two, three, four, one, two, three, four.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Whatever I go, one, two, three, four, five, one, two, three, four, five, and started messing around time signatures. Then I was playing in this band with a great musician who was really Brent Ritzel, who was in this band with me, and he taught me about arranging songs. And it was like, what if we take this part and instead of make it go like back and forth, we make it like a circle?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Or what if we make it like a straight line? you know, or zigzag, you know, just make it like nonlinear in these interesting ways. And then next thing you know, it's like the whole world sort of opens up as like the, and then what I started to realize, especially, so you could appreciate this as a musician, I think. So time signatures, right? So we are so brainwashed to think in four, four, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Every rock song you can think of almost is in four, four. I know you're a Floyd fan. So think of money by Pink Floyd, right? Yeah. Boom. You feel like it's in 4-4 because it resolves itself, but it resolves on the last note. Basically, it resolves on the first note of the next measure. So it's got seven beats instead of eight where the riff is actually happening.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so I just said, well, failure is not an option. And eventually I got out of it and froze and got cut up and The things that we were going through were just insane, but a short version of this is my wife and my daughter and Randy's wife, they gave us all sorts of hell about this because they were ready to send out a search party. So They were giving me hell about it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But you're thinking in 4 because that's how we're used to thinking. So the music flows a little bit faster than it's supposed to. And you're getting a little bit of prediction error every time this is happening. And once I got used to that, I was like, I hate writing in 4-4 because I was like, everything just feels better if I do it in 7-4, if I alternate between 4 and 3 and doing all this stuff.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then it's like, jazz music is like that. They just do so much interesting stuff with this.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, yeah. And it's like, so I'm actually like a very, one of the genres we used to play in was math rock, is what they called it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, I guess it would be like, so instead of, you might go like, instead of playing four beats in every measure, no, no, no, no, no, no, no, no, you go, no, no, no, no, no, no, no, no, no, no, no, no, no, no, no.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
you know and just do these things and then you might arrange it in weird ways so that there might be three measures of verse and then one you know and then five measures of chorus and then two measures so you could just mess around with everything right what does that feel like to listen to there's there's something about symmetry or or like patterns that feel good and like relaxing for us or whatever it feels like home and disturbing that can be quite disturbing yeah so is that
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So, I mean, it depends. So a lot of my style of songwriting is very much like in terms of like repetitive themes, but messing around with structure because I'm not a great guitarist technically. And so I don't play complicated stuff. And there's things you can hear stuff where it's just like so complicated, you know?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Um, but often what I find is, is like having a melody or, and then adding some dissonance to it just enough, and then adding some complexity that gets, gets you going just enough. But I have a high tolerance for, for that kind of dissonance and prediction.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think I have a theory, a pet theory that it's like, basically you can explain most of human behavior as some people are lumpers and some people are splitters, you know? Mm-hmm. And so it's like, some people are very kind of excited when they get this dissonance and they want to like go with it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And some people are just like, no, I want to lump every, you know, I don't know, maybe that's even a different thing, but it's like, basically it's like, I think some people get scared of that discomfort. Yeah. And I really thrive on it. Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
The cover band I play in is a band called Pavlov's Dogs. Yeah. So it's a band, unsurprisingly, of mostly memory researchers, neuroscientists. I love this.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Actually, one of your MIT colleagues, Earl Miller, plays bass.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You could compete if you want. Maybe we could audition you.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Oh, yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Earl's going to kill me. He's very precise.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So it's mostly late 70s punk and 80s new wave and post-punk. Blondie, Ramones, Clash. I sing Age of Consent by New Order and Love Will Tear Us Apart.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, yeah, yeah. Carrie Hoffman and also Paula Croxon. And so they do, yeah, so Carrie does Blondie amazingly well. And we do, like, Gigantic by the Pixies. Paula does that one.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then I started to tell people in my lab about this and then friends, and it just became a better and better story every time. And we actually had some photos of just the crazy things like this generator that was hanging over the water. And we're like ducking under this, they are these metal gratings and I'm like going flat on, and it was just nuts, you know, but it became a great story.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Of someone else's?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Cover, okay. And it's one we do with Pavlov's dogs. Mm-hmm. I really enjoy playing I Want to Be Your Dog by Iggy and the Stooges. Yeah, it's a good song. Which is perfect because we're Pavlov's dogs.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And Pavlov, of course, was like basically created learning theory. So, you know, there's that. But also it's like, but I mean, Iggy and the Stooges, that song. So I play and sing on it, but it's just like it devolves into total noise. Yeah. just like fall on the floor and generate feedback.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I've like, I think in the last version, it might've been that or a velvet underground cover in our last show. I actually, I have a guitar made of aluminum that I got made and I thought this thing's indestructible. And so I kind of like was just, you know, moving it around, had it upside down and all this stuff to generate feedback.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think I broke one of the, I broke one of the tuning pegs and I've had it to break it all metal guitar. Go figure. Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I think the most beautiful, but incredibly hard to put your finger on is this idea of the internal model that it's like, there's everything you see and there's everything you hear and touch and taste, you know, every breath you take, whatever, but it's all connected by this, like, Mm-hmm. And being able to figure out where that comes from and how things are connected to me is just amazing.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But just this idea of like the world in front of us, we're only sampling this little bit and trying to take so much meaning from it. And we do a really good job, not perfect. I mean, you know, but that ability to me is just amazing.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, yeah. You know, it's funny that you mentioned that. So one of the reasons I wrote the book, amongst many, is that I really felt like people needed to hear from scientists. And COVID was just a great example of this, because people weren't hearing from scientists. One of the things I think that people didn't get... was the uncertainty of science and how much we don't know.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think every scientist lives in this world of uncertainty. And when I was writing the book, I just became aware of all of these things we don't know. And so I think of physics a lot. I think of this idea of like,
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it was definitely, I mean, Randy and I were already tight, but that was a real bonding experience for us. And, Yeah. I mean, and I learned from that, that it's like, I don't look back on that enough, actually, because I think we often, at least for me, I don't necessarily have the confidence to think that things will work out, that I'll be able to get through a certain thing.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
overwhelming majority of the stuff that's in our universe cannot be directly measured i used to think haha i hate physics so this is physicists get the nobel prize for doing whatever stupid thing it's like there's 10 physicists out there i'm just kidding just strong words yeah no no no i'm kidding it's the physicists who do neuroscience could be rather opinionated so sometimes i like to dish it's all love it's all love that's right i this is the adhd talking so um uh but
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
At some point, I had this aha moment where I was like, to be aware of that much that we don't know and have a beat on it and be able to go towards it, that's one of the biggest scientific successes that I could think of. You are aware that you don't know about this gigantic section, overwhelming majority of the universe, right? Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think the more what keeps me going to some extent is realizing the changing the scope of the problem and figuring out, oh, my God, there's all these things we don't know. And I thought I knew this because science is all about assumptions. Right. So have you ever read The Structure of Scientific Revolutions by Thomas Kuhn?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
yes that's like my only philosophy really that i've read but it's so brilliant in the way that they frame this idea of like he frames this idea of assumptions being core to the scientific process and the paradigm shift comes from changing those assumptions and this idea of like finding out this kind of whole zone of what you don't know to me is the exciting part you know
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Oh, thank you. It's been a blast.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But my ability to actually get something done in that moment is better than I give myself credit for, I think. And that was the lesson of that story that I really took away.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Absolutely. Yeah. So let's say after this, you and I decided we're going to go for a beer, right? How do you choose where to go? You're probably going to be like, oh, yeah, this new bar opened up near me. I had a great time there. They had a great beer selection. Or you might say, oh, we went to this place and it was totally crowded and they're playing this horrible EDM or whatever. Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So right there, valuable source of information, right? And then you have these things like where you do this counterfactual stuff like, well, I did this previously, but what if I had gone somewhere else and said, maybe I'll go to this other place because I didn't try it the previous time. So there's all that kind of reasoning that goes into it too.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
um i think even if you think about the big decisions in life right it's like you and i were talking before we started recording about how i got into memory research and you got into uh ai and it's like we all have these personal reasons that guide us in these particular directions and some of it's the environment and random factors in life and some of it is memories of things that we want to
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
overcome or things that we build on in a positive way. But either way, they define us.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, I do feel like adolescence is much more important than I think people give credit for. I think that there is this kind of a sense like the first three years of life is the most important part. But The teenage years are just so important for the brain, you know, and so that's where a lot of mental illness starts to emerge.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You know, now we're thinking of things like schizophrenia as a neurodevelopmental disorder because it just emerges during that period of adolescence and early adulthood. So, and I think the other part of it is, is that, you know, as I guess I was a little bit too firm in saying that memory determines who we are. It's really the self is an evolving construct. I think we kind of underestimate that.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And when you're a parent, you feel like every decision you make is consequential in forming this child and plays a role, right? But so do the child's peers. And so do, you know, there's so much. I mean, that's why I think the big part of education I think that's so important is not the content you learn. I mean, think of how much dumb stuff we learned in school, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But a lot of it is learning how to get along with people and learning who you are and how you function. And, you know, that can be terribly traumatizing even if you have a perfect, you know, parents working on you.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, yeah. In fact, actually, I was just talking to my really good friend and colleague, Simona Getty, who studies the neuroscience of child development. And so we were talking about this. And so there are a bunch of reasons, I would say. So one reason is there's an area of the brain called the hippocampus, which is very, very important for remembering events or episodic memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so the first two years of life, there's a period called infantile amnesia. And then the next couple of years of life after that, there's a period called childhood amnesia. And the difference is that basically in the lab and even during childhood and afterwards, children basically don't have any episodic memories for those first two years.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
The next two years, it's very fragmentary, and that's why they call it childhood amnesia. So there's some, but it's not much. So one reason is that the hippocampus is taking some time to develop, but another is the neocortex.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So the whole folded stuff of gray matter all around the hippocampus is developing so rapidly and changing, and a child's knowledge of the world is just massively being built up, right? So
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, I'm going to probably embarrass myself, but it's like if you showed like, you know, you trained a neural network and you give it like the first couple of patterns or something like that, and then you bombard it with another like, you know, year's worth of data, try to get back those first couple of patterns, right? It's like everything changes.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so the brain is so plastic, the cortex is so plastic during that time, and we think that memories for events are very distributed across the brain. So imagine you're trying to get back that pattern of activity that happened during this one moment, But the roads that you would take to get there have been completely rerouted, right? So I think that's my best explanation.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
The third explanation is a child's sense of self takes a while to develop. And so their experience of learning might be more learning what happened as opposed to having this first-person experience of, I remember I was there.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I wouldn't necessarily describe it as a trauma. We can get into this whole stages of life thing, which I just love. Basically, those first few years, there are, I mean, think about it, a kid's internal model of their body is changing, right? It's like just learning to move. I mean, if you ever have a baby, you'll know that the first three months, they're discovering their toes, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it's just nuts, right? So everything is changing. But what's really fascinating is, and I think this is one of those, this is not at all me being a scientist, but it's like one of those things that people talk about when they talk about the positive aspects of children is that they're exceptionally curious and they have this kind of openness towards the world.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so that prediction error is not a negative traumatic thing. I think it's like a very positive thing because it's what they use, they're seeking information. One of the areas that I'm very interested in is the prefrontal cortex. It's an area of the brain that, I mean, I could talk all day about it, but it helps us use our knowledge to say, hey, this is what I want to do now. This is my goal.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So this is how I'm going to achieve it and focus everything towards that goal, right? The prefrontal cortex takes forever to develop in humans. The connections are still being tweaked and reformed like into late adolescence, early adulthood, which is when you tend to see mental illness pop up, right? So it's being massively reformed.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Then you have about 10 years maybe of prime functioning of the prefrontal cortex. And then it starts going down again and you end up being older and you start losing all that frontal function. So I look at this and you'd say, okay, from you sit around episodic memory talks, we'll always say children are worse than adults at episodic memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Older adults are worse than young adults at episodic memory. And I always say, God, this is so weird. Why would we have this period of time that's so short when we're perfect, right? Or optimal. And I like to use the word optimal now because there's such a culture of optimization right now.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it's like, I realized I have to redefine what optimal is because for most of the human condition, I think we had a series of stages of life where you have basically adults saying, okay, young adults saying, I've got a child and, you know, I'm part of this village and I have to hunt and forage and get things done.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I need a prefrontal cortex so I can stay focused on the big picture and long haul goals. Now, I'm a child. I'm in this village. I'm kind of wandering around, and I've got some safety, and I need to learn about this culture because I know so little. What's the best way to do that? Let's explore. I don't want to be constrained by goals as much. I want to really be free. Play and explore and learn.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So you don't want a super tight prefrontal cortex. You don't even know what the goals should be yet, right? It's like, if you're trying to design a model that's based on a bad goal, it's not gonna work well, right? So then you go late in life and you say, oh, why don't you have a great prefrontal cortex then?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But I think, I mean, if you go back and you think, how many species actually stick around naturally long after their childbearing years are over, after their reproductive years are over? Like menopause, from what I understand, menopause is not all that common in the animal world, right? So why would that happen?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so I saw Alison Gopnik said something about this, so I started to look into this, about this idea that, you know, really, when you're older, in most societies, your job is no longer to form new episodic memories. It's to pass on the memories that you already have, this knowledge about the world, what we call semantic memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
to pass on that semantic memory to the younger generations, pass on the culture. Even now in indigenous cultures, that's the role of the elders. They're respected. They're not seen as people who are past it and losing it. And I thought that was a very poignant thing that... Memory is doing what it's supposed to throughout these stages of life.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah. And for the ecology of the system. So I looked into this and it's like another species that has menopause is orcas. Orca pods are led by the grandmothers, right? So not the young adults, not the parents or whatever, the grandmothers. And so they're the ones that pass on the traditions to the, I guess, the younger generation of orcas.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And if you look from what little I understand, different orca pods have different traditions. They hunt for different things. They have different play traditions. And that's a culture, right? And so in social animals... Evolution, I think, is designing brains that are really around, you know, it's obviously optimized for the individual, but also for kin.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think that the kin are part of this, when they're a part of this intense social group, the brain development should parallel the nature of the ecology.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So we can think about this on a number of levels. Maybe I'll give you the simplest version first, which is we tend to think of memories as these individual things, and we can just access them, maybe a little bit like photos on your phone or something like that. But in the brain, the way it works is you have this distributed pool of neurons, and
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
the memories are kind of shared across different pools of neurons. And so what you have is competition where sometimes memories that overlap can be fighting against each other, right? So sometimes we forget because that competition just wipes things out. Sometimes we forget because there aren't the biological signals which we can get into. would promote long-term retention.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And lots of times we forget because we can't find the cue that sends us back to the right memory. And we need the right cue to be able to activate it, right? So for instance, in a neural network, you wouldn't go and you'd say, this is the memory, right? It's like the whole ecosystem of memories is in the weights of the neural network.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And in fact, you could extract entirely new memories depending on how you feed
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
That's exactly right. That's exactly right. And in humans, you have this more complex set of ways memory works. There's, as I said, the knowledge or what you call semantic memory. And then there's these memories for specific events, which we call episodic memory. And so there's different pieces of the puzzle that require different kinds of cues.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So that's a big part of it too, is just this kind of what we call retrieval failure.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, and so memory researchers, we love to cut things up and say, you know, is memory one thing or is it two things? There's two things or there's three things. And so one of the things that there's value in that and especially experimental value in terms of being able to dissect things. In the real world, it's all connected.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Speak to your question, working memory is a term that was coined by Alan Baddeley. It's basically thought to be this ability to keep information online in your mind right in front of you at a given time, and to be able to control the flow of that information, to choose what information is relevant, to be able to manipulate it, and so forth.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And one of the things that Alan did that was quite brilliant was he said, there's this ability to kind of passively store information, see things in your mind's eye or hear your internal monologue. But we have that ability to keep information in mind. But then we also have this separate, what he called a central executive, which is identified a lot with the prefrontal cortex.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's this ability to control the flow of information that's being kept active based on what it is you're doing. Now, a lot of my early work was basically saying that this working memory, which some memory researchers would call short-term memory, is not at all independent from long-term memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
That is that a lot of executive function requires learning and you have to have like synaptic change for that to happen. But there's also transient forms of memory. So one of the things I've been getting into lately is the idea that we form internal models of events. The obvious one that I always use is birthday parties, right? So you go to a child's birthday party.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Once the cake comes out and you just see a candle, you can predict the whole frame, you know, set of events that happens later. And up till that point where the child blows out the candle, you have an internal model in your head of what's going on. And so if you follow people's eyes, it's not actually on what's happening. It's going where the action's about to happen.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
which is just fascinating, right? So you have this internal model, and that's a kind of a working memory product. It's something that you're keeping online that's allowing you to interpret this world around you. Now, to build that model, though, you need to pull out stuff from your general knowledge of the world, which is what we call semantic memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then you'd want to be able to pull out memories for specific events that happened in the past, which we call episodic memory. So... In a way, they're all connected, even though it's different.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
The things that we're focusing on and the way we organize information in the present, which is working memory, will play a big role in determining how we remember that information later, which people typically call long-term memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
We're not at all the first to do this. Jeff Sachs was a big pioneer in this, and I've been working with many other people. Ken Norman, Leila Devachi at Columbia has done some interesting stuff with this.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
There's this idea that we form these internal models at particular points of high prediction error or points of, I believe, also points of uncertainty, points of surprise or motivationally significant periods. And those points are when it's maximally optimal to encode an episodic memory. So I used to think, oh, well, we're just encoding episodic memories constantly, boom, boom, boom, boom, boom.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But think about how much redundancy there is in all that, right? It's just a lot of information that you don't need. But if you capture an episodic memory at the point of maximum uncertainty for the singular experience, it's only gonna happen once. But if you capture it at the point of maximum uncertainty or maximum surprise, you have the most useful point in your experience that you've grabbed.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And what we see is that the hippocampus and these other networks that are involved in generating these internal models of events, they show a heightened period of connectivity or correlated activity during those breaks between different events, which we call event boundaries. These are the points where you're surprised or you cross from one room to another and so forth.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And that communication is associated with a bump of activity in the hippocampus and better memory. And so if people have a very good internal model throughout that event you don't need to do much memory processing you're in a predictive mode right and so then at these event boundaries you encode and then you retrieve and you're like okay wait a minute what's going on here
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Ranganath is now talking about orcas. What's going on? And maybe you have to go back and remember reading my book to pull out the episodic memory to make sense of whatever it is I'm babbling about, right? And so there's this beautiful dynamics that you can see in the brain of these different networks that are coming together and then de-affiliating at different points in time.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
that are allowing you to go into these modes. And so to speak to your original question, to some extent when we're talking about semantic memory and episodic memory and working memory, you can think about it as these processes that are unfolding as these networks kind of come together and pull apart.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I think improvement, it depends on what your definition of optimal is. So what I say in the book is that you don't want to remember more. You want to remember better, which means focusing on the things that are important. And that's what our brains are designed to do.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So if you go back to the earliest quantitative studies of memory by Ebbinghaus, what you see is that he was trying so hard to memorize this arbitrary nonsense. And within a day, he lost about 60% of that information. And he was basically using a very, very generous way of measuring it, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So as far as we know, nobody has managed to violate those basics of having people forget most of their experiences. So if your expectation is that you should remember everything and that's what your optimal is, you're already off because this is not what human brains are designed to do. On the other hand,
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
what we see over and over again is that the brain does basically one of the cool things about the design of the brain is it's always less is more, less is more, right? It's like, I mean, I've seen estimates that the human brain uses something like 12 to 20 Watts, you know, in a day. I mean, that's just nuts, the low power consumption, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So it's all about reusing information and making the most of what we already have. And so, um, That's why basically, again, what you see biologically is neuromodulators, for instance, these chemicals in the brain like norepinephrine, dopamine, serotonin. These are chemicals that are released during moments that tend to be biologically significant—surprise, fear, stress, etc.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so these chemicals promote lasting plasticity, right? Essentially, some mechanisms by which the brain can prioritize the information that you carry with you into the future. Attention is a big factor as well, our ability to focus our attention on what's important. And so there's different schools of thought. On training attention, for instance.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So one of my colleagues, Amishi Jha, she wrote a book called Peak Mind and talks about mindfulness as a method for improving attention and focus. So she works a lot with military like Navy SEALs and stuff to do this kind of work.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
um with mindfulness meditation um adam gazali another one of my friends and colleagues has work on kind of training through video games actually as a way of training attention and so uh it's not clear to me you know one of the challenges though in training is you tend to overfit to the thing that you're trying to optimize right so you tend to if i'm looking at a video game and
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I can definitely get better at paying attention in the context of the video game, but you transfer it to the outside world. That's very controversial.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
i can say that in fact we do in certain ways right so if you are an expert in something you are training attention so we did this one study of expertise in the brain and uh you know so people used to think let's say if you're a bird expert or something right people will go like if you get really into this world of birds you start to see the differences in your visual cortex is tuned up and it's all about plasticity of the visual cortex and vision researchers love to say everything's visual but
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But it's like we did this study of attention and working memory and expertise. And one of the things that surprised us were the biggest effects as people became experts in identifying these different kinds of just crazy objects that we made up.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
As they developed this expertise of being able to identify what made them different from each other and what made them unique, we were actually seeing massive increases in activity in the prefrontal cortex. And this fits with some of the studies of chess experts and so forth, that it's not so much that you learn the patterns passively, you learn what to look for.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You learn what's important, what's not, right? And you can see this in any kind of expert professional athlete. They're looking three steps ahead of where they're supposed to be. So that's a kind of a training of attention. And those are also what you'd call expert memory skills. So if you take the memory athletes, I know that's something we're both interested in.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So these are people who train in these competitions and they'll memorize like a deck of cards in like a really short amount of time. There's a great memory athlete, her name I think is pronounced Yenya Wintersoul. So I think she's got like a giant Instagram following. And so she had this YouTube video that went viral where she had memorized an entire IKEA catalog, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so how do people do this? By all accounts, from people who become memory athletes, they weren't born with some extraordinary memory, but they practice strategies over and over and over again. The strategy that they use for memorizing a particular thing, it can become automatic and you can just deploy it in an instant, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So again, it's not necessarily going to, one strategy for learning the order of a deck of cards might not help you for something else that you need, like, you know, remembering your way around Austin, Texas. But it's going to be these, whatever you're interested in, you can optimize for that. And that's just a natural byproduct of expertise.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Oh, yeah. Okay, we can come back to this. But yeah, go on.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So I feel like we've got a lot in common because when people introduce themselves to me, it's almost like I have this just blank blackout for a moment. And then I'm just looking at them like, what happened? I look away or something. What's wrong with me? So, I mean, I'm totally with you on this. The reason why it's hard is that there's no reason we should be able to remember names.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But for the most part, it's like these names are just utterly arbitrary. So you have no thing to latch onto. And so it's not really a thing that our brain does very well to learn meaningless, arbitrary stuff. So what you need to do is build connections somehow, visualize a connection. And sometimes it's obvious or sometimes it's not. I'm trying to think of a good one for you now, but
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But the first thing I think of is Lex Luthor. That's great.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I know he has a shaved head, though, or he's bald, which you're not. You've got a great head. I'd trade hair with you any day. But something like that. But if I can come up with something. Like I could say, okay, so Lex Luthor is this criminal mastermind.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah. Yeah. And I, but I'm serious though, that these kinds of weird associations now I'm building a richer network. I mean, one of the things that I find is if I've like, you can have somebody's name, that's just totally generic, like John Smith or something. Not that no offense to people that, that name, but you know, if I, if I see a generic name like that,
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
but I've read John Smith's papers academically and then I meet John Smith at a conference, I can immediately associate that name with that face because I have this pre-existing network to lock everything into, right? And so you can build that network and that's what the method of loci or the memory palace technique is all about.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
is you have a preexisting structure in your head of like your childhood home or this mental palace that you've created for yourself. And so now you can put arbitrary pieces of information in different locations in that mental structure of yours. And then you could walk through the different path and find all the pieces of information you're looking for.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So the method of loci is a great method for just learning arbitrary things because it allows you to link them together and get that cue that you need to pop in and find everything, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Oh, yeah, absolutely, absolutely. And I think the principle here is, again, I was telling you this idea that memories can compete with each other, right? Right. Well, I like to use this example, and maybe someday I'll regret this, but I've used it a lot recently. Imagine if this were my desk, it could be cluttered with a zillion different things, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So imagine it's just cluttered with a whole bunch of yellow Post-it notes, and on one of them I put my bank password on it, right? Well, it's going to take me forever to find it. It's just going to be buried under all these other Post-it notes. But if it's like hot pink... It's going to stand out, and I find it really easily, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So that's one way in which if things are distinctive, if you've processed information in a very distinctive way, then you can have a memory that's going to last. And that's very good, for instance, for name-face associations. If I get something distinctive about you, you know, that it's like...
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You've got very short hair and maybe I can make the association with Lex Luthor that way or something like that, right? But I get something very specific. That's a great cue. But the other part of it is what if I just organized my notes so that I have my finances in one pile and I have my reminders, my to-do list in one pile and so forth, so I organize them.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, then I know exactly if I'm going for my banking, my bank password, I could go to the finance pile, right? Yeah. So the method of loci works, or memory palaces work, because they give you a way of organizing.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
There's a school of thought that says that episodic memory evolved from this kind of knowledge of space and basically these primitive abilities to figure out where you are, and so people explain the method of loci that way. And whether or not the evolutionary argument is true, the method of loci is not at all special. So if you're not a good visualizer, stories are a good one.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So a lot of memory athletes will use stories and they'll go like, if you're memorizing a deck of cards, they have a little code for the different, like the king and the jack and the 10 and so forth. And they'll make up a story about things that they're doing and that'll work.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
songs are a great one right i mean it's like uh i can still remember there's this obscure episode of the tv show cheers they sing a song about albania that he uses to memorize all these facts about albania and i could still sing that song to you it's it's just i saw it on a tv show you know
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Oh, yeah. If I'm trying to memorize something, let's say if I have an hour to memorize as many Spanish words as I can, if I just try to do like half an hour and then later in the day I do half an hour, I won't retain that information as long as if I do half an hour today and half an hour one week from now. And so doing that extra spacing... should help me retain the information better.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Now, there's an interesting boundary condition, which is it depends on when you need that information. So many of us, for me, I can't remember so much from college and high school because I crammed, because I just did everything at the last minute. And sometimes I would literally study in the hallway right before the test, and that was great.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Because what would happen is, is I just had that information right there. And so actually not spacing can really help you if you need it very quickly, right? But the problem is, is that you tend to forget it later on. But on the other hand, if you space things out, you get a benefit for later on retention. And so there's many different explanations. We have a computational model of this.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's currently under revision. But in our computer model, what we say is that maybe a good way of thinking about this is this conversation that you and I are having. it's associated with a particular context, a particular place in time. And so all of these little cues that are in the background, these little guitar sculptures that you have and that big light umbrella thing, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
All these things are part of my memory for what we're talking about, the content. So... Now, later on, you're sitting around and you're at home drinking a beer and you think, God, what a strange interview that was, right? So now you're trying to remember it, but the context is different. So your current situation doesn't match up with the memory that you pulled up. There's error.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
There's a mismatch between what you pulled up and your current context. And so in our model, what you start to do is you start to erase or alter the parts of the memory that are associated with a specific place and time, and you heighten the information about the content. And so if you remember this information in different times and different places,
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's more accessible at different times in different places because it's not overfitted in an AI kind of way of thinking about things. It's not overfitted to one particular context. But that's also why the memories that we call upon the most also feel kind of like they're just things that we read about almost. You don't vividly reimagine them.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's like they're just these things that just come to us like facts. And it's a little bit different than semantic memory, but it's like basically these events that we have recalled over and over and over again, we keep updating that memory so it's less and less tied to the original experience.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But then we have those other ones, which it's like you just get a reminder of that very specific context. You smell something, you hear a song, you see a place that you haven't been to in a while, and boom, it just comes back to you. And that's the exact opposite of what you get with spacing, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, but at the same time, it becomes stronger in the sense that the content becomes stronger.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah. And I think this falls into a category. We've done other modeling. One of these is a published study in PLOS, Computational Biology, where we showed that another way, which is, I think, related to the spacing effect is what's called the testing effect. So the idea is that if you're trying to learn words...
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
let's say in Spanish or something like that, and this doesn't have to be words, it could be anything, you test yourself on the words, and that act of testing yourself helps you retain it better over time than if you just studied it, right? And so... From traditional learning theories, some learning theories anyway, this seems weird.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Why would you do better giving yourself this extra error from testing yourself rather than just giving yourself perfect input that's a replica of what it is that you're trying to learn? And I think the reason is is that you get better retention from that error, that mismatch that we talked about, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So what's happening in our model, it's actually conceptually kind of similar to what happens with backprop in AI or neural networks. And so the idea is that you expose, here's the bad connections and here's the good connections. And so we can keep the parts of this cell assembly that are good for the memory and lose the ones that are not so good.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But if you don't stress test the memory, you haven't exposed it to the error fully. And so that's why I think this is kind of this is a thing that I come back to over and over again is that you will retain information better if you're constantly pushing yourself to your limit. Right. If you are feeling like you're coasting, then you're actually not learning.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, and feel good about it. Even though everyone tells me, oh, my memory's terrible, in the moment, they're overconfident about what they'll retain later on. So it's fascinating. And so what happens is when you test yourself, you're like, oh my God, I thought I knew that, but I don't. And so it can be demoralizing until you get around that and you realize, hey, this is the way that I learned.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
This is how I learned best. It's like if you're trying to, you know, star in a movie or something like that, you don't just sit around reading the script. You actually act it out, and you're going to botch those lines from time to time, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
One of the cool things that I found is that some people really just revolutionize a field by creating a problem that didn't exist before. It's kind of like why I love science. Engineering is like solving other people's problems, and science is about creating problems. I'm just much more like I want to break things and create problems. Not necessarily move fast, though. Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But one of my former mentors, Marsha Johnson, who in my opinion is one of the greatest memory researchers of all time, she comes up, young woman in the field, and it's mostly guy field, and she gets into this idea of how do we tell the difference between things that we've imagined and things that we actually remember? How do we tell, I get some mental experience.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Where did that mental experience come from, right? And it turns out this is a huge problem, right? Because essentially our mental experience of remembering something that happened, our mental experience of thinking about something, how do you tell the difference? They're both largely constructions in our head. And so it is very important.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And the way that you do it is, I mean, it's not perfect, but the way that we often do it and succeed is by, again, using our prefrontal cortex and really focusing on the sensory information or the place and time and the things that put us back into when this information happened.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And if it's something you thought about, you're not going to have all of that vivid detail as you do for something that actually happened. But it doesn't work all the time. But that's a big thing that you have to do. But it takes time. It's slow and it's, again, effortful. But that's what you need to remember accurately.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But what's cool, and I think this is what you alluded to about how that was an interesting experience, is imagination is exactly the opposite. Imagination is basically saying, I'm just going to take all this information from memory, recombine it in different ways, and throw it out there. And so, for instance, Dan Schachter and Donna Addis have done cool work on this.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Demis Hassabis did work on this with Eleanor McGuire in UCL. And this goes back actually to this guy, Frederick Bartlett, who was this revolutionary memory researcher. Bartlett, he actually rejected the whole idea of quantifying memory. He said, there's no statistics in my book. He came from this anthropology perspective. And short version of the stories. He just asked people to recall things.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
He would give people stories and poems, ask people to recall them. And what he found was people's memories didn't reflect all of the details of what they were exposed to, and they did reflect a lot more. They were filtered through this lens of prior knowledge. The cultures that they came from, the beliefs that they had, the things they knew.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so what he concluded was that he called remembering an imaginative construction, meaning that we don't replay the past. We imagine how the past could have been by taking bits and pieces that come up in our heads.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And likewise, he wrote this beautiful paper on imagination saying when we imagine something and create something, we're creating it from these specific experiences that we've had and combining it with our general knowledge. But instead of trying to focus it on being accurate and getting at one thing, you're just ruthlessly recombining things without any necessary kind of goal in mind.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, or at least that's one kind of creation.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I think so. I mean, it's not clear that it is in everyone, but one of the things that's been studied is some patients who have amnesia, for instance, they have brain damage, say, to the hippocampus. And if you ask them to imagine things that are not in front of them, like imagine what could happen after I leave this room, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
They find it very difficult to give you a scenario of what could happen. Or if they do, it would be more stereotyped, like, yes, this would happen. But it's not like they can come up with anything that's very vivid and creative in that sense. And it's partly because when you have amnesia, you're stuck in the present, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Because to get a very good model of the future, it really helps to have episodic memories to draw upon, right? And so that's the basic idea. And in fact, one of the most impressive things, when people started to scan people's brains and ask people to remember past events, what they found was there was this big network of the brain called the default mode network.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
it gets a lot of press because it's like thought to be important. It's engaged during mind wandering. And if I ask you to pay attention to something, it only comes on when you stop paying attention, you know, so people, Oh, it's just this kind of, you know, daydreaming network. And I thought, this is just ridiculous research. Who cares? You know?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Um, but then what people found was when people recall episodic memories, this network gets active and, um, So we started to look into it, and this network of areas is really closely, functionally interacting with the hippocampus. And so, in fact, some would say the hippocampus is part of this default network.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And if you look at brain images of people, or brain maps of activation, so to speak, of people imagining possible scenarios of things that could happen in the future, or even things that couldn't really be very plausible... they look very similar. I mean, you know, to the naked eye, they look almost the same as maps of brain activation when people remember the past.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
According to our theory, and we've got some data to support this, we've broken up this network into various sub-pieces, is that basically it's kind of taking apart all of our experiences and creating these little Lego blocks out of them.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then you can put them back together if you have the right instructions to recreate these experiences that you've had, but you could also reassemble them into new pieces to create a model of an event that hasn't happened yet. And that's what we think happens. And our common ground that we're establishing in language requires using those building blocks to put together a model of what's going on.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
One of the few literature books that I've read, I should say. I read a lot in school that I don't remember, but Brothers Karamazov.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, there was actually this famous mnemonist. He's kind of like back then the equivalent of a memory athlete, except he would go to shows and do this. That was described by this really famous neuropsychologist from Russia named Luria.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so this guy was named Solomon Cheryshevsky, and he had this condition called synesthesia that basically created these weird associations between different senses that normally wouldn't go together. So that gave him this incredibly vivid imagination that he would use to basically imagine all sorts of things that he would need to memorize.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And he would just imagine, like, just create these incredibly detailed things in his head that allowed him to memorize all sorts of stuff. But it also really haunted him by some reports that basically it was like he was at some point, you know, and again, who knows if the drinking was part of this, but at some point had trouble differentiating his imagination from reality, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And this is interesting because it's like, I mean, that's what psychosis is in some ways is you, you know, first of all, you're just learning connections from prediction errors that you probably shouldn't learn. And the other part of it is that your internal signals are being confused with actual things in the outside world, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, I mean, it might be why there's such an interesting relationship between genius and psychosis.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I think so. Sometimes scary, but mostly fascinating.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
There's a guy named Henry Rodger who's studying these guys, and there's actually a book by Joshua Foer called Moonwalking with Einstein where he talks about he actually, as part of this book, just decided to become a memory athlete. They often have these life events that make them go... Hey, why don't I do this?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So there was a guy named Scott Hagwood, who I write about, who thought that he was he was getting chemo for cancer. And so he decided, like, because the chemo there's a well-known thing called chemo brain where people become like they just lose a lot of their sharpness. And so he wanted to fight that by learning these memory skills. So he bought a book.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And this is the story you hear in a lot of memory athletes is they buy a book by other memory athletes or other memory experts, so to speak. And they just learn those skills and practice them over and over again. They start by winning bets and so forth, and then they go into these competitions.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And the competitions are typically things like memorizing long strings of numbers or memorizing orders of cards and so forth. So there tend to be pretty arbitrary things, not like things that you'd be able to bring a lot of prior knowledge. But they build the skills that you need to memorize arbitrary things.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I've really been most excited about going in the opposite direction and using things that are more and more naturalistic. And the reason is that we've moved in that direction because what we found is that memory works very, very differently when you study memory in the way that people typically remember.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so it goes into a much more predictive mode, and you have these event boundaries, for instance. But a lot of what happens is this kind of fascinating mix that we've been talking about, a mix of interpretations and imagination with perception. And the new direction we're going in is understanding navigation in our memory-first places.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And the reason is, is that there's a lot of work that's done in rats, which is very good work. They have a rat and they put it in a box and the rat goes, chases cheese in a box, you know, find cells in the hippocampus that fire when a rat is in different places in the box. And so the conventional wisdom is that the hippocampus forms this map of the box and
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think that probably may happen when you have absolutely no knowledge of the world, right? But I think one of the cool things about human memory is we can bring to bear our past experiences to economically learn new ones. And so, for instance, if you learn a map of an Ikea—let's say if I go to the Ikea in Austin, I'm sure there's one here—
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I probably could go to this IKEA and find my way to the, you know, where the wine glasses are without having to even think about it because it's got a very similar layout, even though IKEA is a nightmare to get around. Once I learned my local IKEA, I can use that map everywhere. Why form a brand new one for a new place? Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so that kind of ability to reuse information really comes into play when we look at things that are more naturalistic tasks. And another thing that we're really interested in is this idea of what if instead of basically mapping out every coordinate in a space, you form a pretty economical graph that connects basically the major landmarks together and being able to use that as information
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
you know, emphasizing the things that are most important, the places that you go for food and the places that are landmarks that help you get around and then filling in the blanks for the rest. Because I really believe that cognitive maps or mental maps of the world, just like our memories for events are not photographic.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I think there's this combination of actual verifiable details and then a lot of inference that you make.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
There's a lot of variability, I think, and there's a lot of disagreement about how people represent locations. In a world of GPS and physical maps, people can learn it from basically what they call a survey perspective, being able to see everything. And so That's one way in which humans can do it that's a little bit different. There's one way which we can memorize roots.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Like I know how to get from here to, let's say if I walk here from my hotel, I can just rigidly follow that route back, right? And there's another more integrative way, which would be what's called a cognitive map, which would be kind of a sense of how everything relates to each other. And so there's lots of people who believe that these maps that we have in our head are isomorphic with the world.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
They're like these literal coordinates that follow Euclidean space. And as you know, Euclidean mathematics is very constrained, right? And I think that we are actually much more generative in our maps of space so that we do have these bits and pieces. And we've got a small task. It's right now, not yet. We need to do some work on it for further analyses.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But one of the things we're looking at is these signals called ripples in the hippocampus, which are these bursts of activity that you see that are synchronized with areas in the neocortex, in the default network, actually. And so what we find is that those ripples seem to increase at navigationally important points when you're making a decision or when you reach a goal.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So this speaks to the emotion thing, right? Because if you have limited choices, if I'm walking down a street, I could really just get a mental map of the neighborhood with a more minimal kind of thing by just saying, here's the intersections and here's the directions I take to get in between them. And what we found in general in our MRI studies is that
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Basically, the more people can reduce the problem, whether it's space or any kind of decision-making problem, the less the hippocampus encodes. It really is very economical towards the points of highest information content and value.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, so this is really interesting. There are these oscillations, right? So there's these waves that you basically see. And these waves are points of very high excitability and low excitability. And at least during, they happen actually during slow wave sleep too. So the deepest stages of sleep when you're just zonked out, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You see these very slow waves where it's like very excitable and then very unexcitable. It goes up and down. And on top of them, you'll see these little sharp wave ripples. And when there's a ripple in the hippocampus, you tend to see a sequence of cells that resemble a sequence of cells that fire when an animal is actually doing something. So it almost is like a little, people call it replay.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I think it's a little bit, I don't like that term, but it's basically a little bit of a compressed play of the sequence of activity in the brain that was taking place earlier. And during those moments, there's a little window of communication between the hippocampus and these areas in the neocortex.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so that, I think, helps you form new memories, but it also helps you, I think, stabilize them, but also really connect different things together in memory and allows you to build bridges between different events that you've had. And so this is one of, at least, our theories of memory. sleep and its real role in helping you see the connections between different events that you've experienced.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
The connections between different events, right? So it's like you see me now, you see me next week, you see me a month later. You start to build a little internal model of how I behave and what to expect of me. And we think sleep, one of the things that allows you to do is figure out those connections and connect the dots and find the signal and the noise.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And this is actually the reason why I got into this whole field of science. When I was in grad school, fMRI was just really taking off as a technique for studying brain activity. And what's beautiful about it is you can study the whole human brain, and there's lots of limits to it, but you can basically do it in person without sticking anything into their brains. And very non-invasive.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, for me, being an MRI scanner is like being in the womb. I just fall asleep. Yeah. If I'm not being asked to do anything, I get very sleepy, you know. But you can have people watch movies while they're being scanned, or you can have them do tests of memory, like giving them words and so forth to memorize.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But what MRI is itself is just this technique where you put people in a very high magnetic field. Typical ones we would use would be 3 Tesla, to give you an idea. Yeah. So a 3-tesla magnet, you put somebody in, and what happens is you get this very weak but measurable magnetization in the brain. And then you apply a radiofrequency pulse, which is basically a different electromagnetic field.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so you're basically using water, the water molecules in the brain as a tracer, so to speak. And part of it in fMRI is the fact that these magnetic fields that you mess with by manipulating these radio frequency pulses and the static field, and you have things called gradients which change the strength of the magnetic field in different parts of the head.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So we tweak them in different ways, but the basic idea that we use in fMRI is that blood is flowing to the brain. And when you have blood that doesn't have oxygen on it, it's a little bit more magnetizable than blood that does, because you have hemoglobin that carries the oxygen, the iron, basically, in the blood that makes it red.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so that hemoglobin, when it's deoxygenated, actually has different magnetic field properties than when it has oxygen. And it turns out when you have an increase in local activity in some part of the brain, the blood flows there. And as a result, you get a lower concentration of hemoglobin that is not oxygenated. And then that gives you more signal.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So I gave you, I think I sent you a gif, as you like to say.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
We could have called it a stern rebuke, perhaps.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
This would be basically a whole movie of fMRI data. And so when you look at it, it's not very impressive. It looks like these very pixelated maps of the brain, but it's mostly kind of like white. But these tiny changes in the intensity of those signals that you probably wouldn't be able to visually perceive, like about 1%, can be statistically very, very large effects for us.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And that allows us to see, hey, there's an increase in activity in some part of the brain when I'm doing some tasks like trying to remember something. And I can use those changes to even predict, is a person going to remember this later or not? And the coolest thing that people have done is to decode what people are remembering from the patterns of activity.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Because maybe when I'm remembering this thing, like I'm remembering the house where I grew up, I might have one pixel that's bright in the hippocampus and one that's dark. And if I'm remembering something more like the car that I used to drive when I was 16, I might see the opposite pattern where a different pixel is bright.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so all that little stuff that we used to think of noise, we can now think of almost like a QR code for memory, so to speak, where different memories have a different little pattern.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
pattern of bright pixels and dark pixels and so this really revolutionized my research so there's fancy research out there where people really i mean not even that i mean by your standards would be stone age but you know applying machine learning techniques to do decoding and so forth and now there's a lot of forward encoding models and you can go to town with this stuff right so
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I'm much more old school of designing experiments where you basically say, okay, here's a whole web of memories that overlap in some way, shape, or form. Do memories that occurred in the same place have a similar QR code? And do memories that occurred in different places have a different QR code?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And you can just use things like correlation coefficients or cosine distance to measure that stuff, right? Super simple, right? And so what happens is you can start to get a whole state space of how a brain area is indexing all these different memories.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it's super fascinating because what we could see is this little like separation between how certain brain areas are processing memory for who was there. And other brain areas are processing information about where it occurred or the situation that's kind of unfolding. And some are giving you information about what are my goals that are involved and so forth.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And the hippocampus is just putting it all together into these unique things that just are about when and where it happened.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So to speak. Let me try a different analogy, too, that might be more accessible for people, which would be like you've got a folder on your computer, right? And you open it up. There's a bunch of files there. I can sort those files by alphabetical order, and now things that both start with the letter A are lumped together, and things that start with Z versus A are far apart, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so that is one way of organizing the folder, but I could do it by date. And if I do it by date, things that were created close together in time are close, and things that are far apart in time are far. So, you can think of how a brain area or a network of areas contributes to memory by looking at what the sorting scheme is.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And these QR codes that we're talking about that you get from fMRI allow you to do that. And you can do the same thing if you're recording from massive populations of neurons in an animal. And you can do it for recording local potentials in the brain, so little waves of activity in, let's say, a human who has epilepsy, and they stick electrodes in their brain, try to find the seizures.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So that's some of the work that we're doing now. But all these techniques basically allow you to say, hey, what's the sorting scheme? We've found that some networks of the brain sort information in memory according to who was there. We've actually shown one of my favorite studies of all time that was done by a former postdoc, Zach Rea.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Zach did the study where we had a bunch of movies with different people in my labs. There are two different people, and he filmed them at two different cafes and two different supermarkets.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And what you could show is in one particular network, you could find the same kind of pattern of activity, more or less, a very similar pattern of activity every time I saw Alex in one of these movies, no matter where he was, right? And I could see another one that was like a common pattern that happened every time I saw this particular supermarket nugget.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it didn't matter whether you're watching a movie or whether you're recalling the movie. It's the same kind of pattern that comes up, right? It's so fascinating. It's fascinating. So now you have those building blocks for assembling a model of what's happening in the present. Right.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
imagining what could happen and remembering things very economically from putting together all these pieces so that all the hippocampus has to do is get the right kind of blueprint for how to put together all these building blocks.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, I mean, it's very slow. To the brain, 50 milliseconds is like, you know, like it's an eternity. Maybe not 50, you know, maybe like, you know, let's say half a second, 500 milliseconds longer. Just so much back and forth stuff happens in the brain in that time, right? So in fMRI, you can measure these magnetic field responses about six seconds after that burst of activity would take place.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
All these things, it's like, is it a feature or is it a bug, right? So one of the interesting things that's been discovered about fMRI is it's not so tightly related to the spiking of the neurons. So we tend to think of the computation, so to speak, as being driven by spikes, meaning like there's just a burst of, it's either on or it's off, and the neuron's like going up or down.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But sometimes what you can have is these states where the neuron becomes a little bit more excitable or less excitable. And so fMRI is very sensitive to those changes in excitability. Actually, one of the fascinating things about fMRI is where does that... How is it we go from neural activity to essentially... blood flow to oxygen, you know, all this stuff.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's such a long chain of, you know, going from neural activity to magnetic fields. And one of the theories that's out there is, you know, most of the cells in the brain are not neurons. They're actually these support cells called glial cells. And one big one is astrocytes. And they play this big role in regulating, you know, kind of being a middle man, so to speak, with the neurons.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So if you, for instance, like one neuron's talking to another, you release a neurotransmitter, like let's say glutamate. And that gets another neuron starts getting active after you release it in the gap between the two neurons called synapse. So what's interesting is if you leave that, you know, imagine you're just flooded with this like liquid in there, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
If you leave it in there too long, you just excite the other neuron too much and you can start to basically get seizure activity. You don't want this. So you got to suck it up. And so actually what happens is these astrocytes, one of their functions is to suck up the glutamate from the synapse.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And that is a massively, and then break it down and then feed it back into the neurons so that you can reuse it. But that cycling is actually very energy intensive. And what's interesting is, at least according to one theory, they need to work so quickly that they're working on metabolizing the glucose that comes in without using oxygen, kind of like anaerobic metabolism.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So they're not using oxygen as fast as they are using glucose. So what we're really seeing in some ways may be in fMRI, not the neurons themselves being active, but rather the astrocytes, which are meeting the metabolic demands of the process of keeping the whole system going.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Oh, well, this gets me to the other part. So now let's say, for instance, if I'm just kind of like, I'm talking to you, but I'm kind of paying attention to your cowboy hat, right? So I'm looking off to the right. I'm thinking about the right, even if I'm not looking at it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
What you'd see is that there would be this little elevation in activity in areas in the visual cortex, which process vision, around that point in space. So if then something happened, like suddenly a light flashed in that part right in front of your cowboy hat, I would have a bigger response to it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But what you see in fMRI is even if I don't see that flash of light, there's a lot of activity that I can measure because you're kind of keeping it excitable. And that in and of itself, even though I'm not seeing anything there that's particularly interesting, there's still this increase in activity. And so it's more sensitive with fMRI. So is that a feature or is it a bug?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Some people who study spikes in neurons would say, well, that's terrible. We don't want that. Likewise, it's slow. And that's terrible for measuring things that are very fast. But one of the things that we found in our work was when we give people movies and when we give people stories to listen to, a lot of the action is in the very, very slow stuff.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's in, because if you're thinking about like a story, let's say you're listening to a podcast or you're listening to the Lex Friedman podcast, right? You're putting this stuff together and building this internal model over several seconds, right? which is basically we filter that out when we look at electrical activity in the brain because we're interested in this millisecond scale.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's almost massive amounts of information, right? So the way I see it is every technique gives you a little limited window into what's going on. fMRI has huge problems. People lie down in the scanner. There's parts of the brain where I'll show you in some of these images where you'll see gaping holes because you can't keep the magnetic field stable in those spots.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You'll see parts where it's like there's a vein and so it just produces big increase and decrease in signal or respiration that causes these changes. There's lots of artifacts and stuff like that. Every technique has its limits. If I'm lying down in an MRI scanner, I'm lying down. I'm not interacting with you in the same way that I would in the real world.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But at the same time, I'm getting data that I might not be able to get otherwise. And so different techniques give you different kinds of advantages.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
there's so many it's really so hard to summarize it I mean I think it's funny because it's like when you're in the field you can get kind of blase about this stuff but then once I started to write the book I was like oh my god this is really interesting how did we do all this stuff um
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I would say that some of the, I mean, you know, from the first studies, just showing how much we forget is very important. Showing how much schemas, which is our organized knowledge about the world, increase our ability to remember information, just massively increase it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Studies of expertise showing how experts like chess experts can memorize so much in such a short amount of time because of the schemas they have for chess. But then also showing that those lead to all sorts of distortions in memory. The discovery that the act of remembering can change the memory, can strengthen it, but it can also distort it if you get misinformation at the time.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it can also strengthen or weaken other memories that you didn't even recall. So just this whole idea of memory as an ecosystem I think was a big discovery. This idea of breaking up our continuous experience into these discrete events I think was a major discovery.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Maybe, yeah. I mean, you know, and again, there's controversial ideas about this, right? But it's like, yeah, this idea that, and this gets back to just this common experience of you walk into the kitchen and you're like, why am I here? And you just end up grabbing some food from the fridge. And then you go back and you're like, oh, wait a minute, I left my watch in the kitchen.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
That's what I was looking for. Mm-hmm. And so what happens is that you have a little internal model of where you are, what you're thinking about. And when you cross from one room to another, those models get updated. And so now when you're in the kitchen, you have to go back and mentally time travel back to this earlier point to remember what it was that you went there for.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so these event boundaries, turns out like in our research, and again, I don't want to make it sound like we've figured out everything, but in our research, one of the things that we found is that Basically, as people get older, the activity in the hippocampus at these event boundaries tends to go down.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But independent of age, if I give you outside of the scanner, you're done with the scanner, I just scan you while you're watching a movie, you just watch it. You come out, I give you a test of memory for stories.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
What happens is you find this incredible correlation between the activity in the hippocampus at these singular points in time, these event boundaries, and your ability to just remember a story outside of the scanner later on. So it's marking this ability to encode memories, just these little snippets of neural activity. So I think that's a big one.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
There's all sorts of work in animal models that I can get into, you know, sleep. I think there's so much interesting stuff that's being discovered in sleep right now. Being able to just record from large populations of cells and then be able to relate that.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think the coolest thing gets back to this QR code thing, because like what we can do now is like I can take fMRI data while you're watching a movie. Or let's do better than that. Let me get fMRI data while you use a joystick to move around in virtual reality. So you're in the metaverse, whatever, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But it's kind of a crappy metaverse because there's always so much metaversing you can do in an MRI scanner. So you're doing this crappy metaversing. So now I can take a rat
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
record from his hippocampus and prefrontal cortex and all these areas with these really new electrodes to get massive amounts of data and have it move around on a trackball in virtual reality in the same metaverse that I did and record that rat's activity. I can get a person with epilepsy who have electrodes in their brain anyway to try to figure out where the seizures are coming from.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And if it's a healthy part of the brain, record from that person, right? And I can get a computational model. And one of the brand new members in my lab, Tyler Bond, is just doing some great stuff. He relates computer vision models and looks at the weaknesses of computer vision models and relates it to what the brain does well. Nice.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so you can actually take a ground truth code for the metaverse, basically, and you can feed in the visual information, let's say the sensory information or whatever that's coming in, to a computational model that's designed to take real-world inputs, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And you could basically tie them all together by virtue of the state spaces that you're measuring in neural activity, in these different formats, in these different species, and in the computational model, which I just find that mind-blowing. You could do... different kinds of analyses on language and basically come up with... Basically, it's the guts of LLMs, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You could do analyses on language, and you could do analyses on sentiment analyses of emotions and so forth, and put all this stuff together. I mean, it's almost too much, but... If you do it right and you do it in a theory-driven way, as opposed to just throwing all the data at the wall and see what sticks, I mean, that to me is just exceptionally powerful.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah. Yeah. I mean, more or less, I mean, there's a lot of details, but yes, I think, and not just fMRI, but you can relate it to, like I said, recordings from large populations of neurons that could be taken in a human or even in a non-human animal that is, you know, where you think it's an anatomical homologue. So that's just mind blowing to me.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Despite all of your rage at GIFs, you're still just a rat in a cage.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Good callback. See, these memory retrieval exercises I'm doing are actually helping you build a lasting memory of this conversation.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, yeah. So, okay. So, let's go to the... So, I think I've got great colleagues who I talk to who study memory in mice, and there's some... One of the valuable things in those models is you can study neural circuits in an enormously targeted way because you could do these genetic studies, for instance, where you can manipulate...
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
particular groups of neurons, and it's just getting more and more targeted to the point where you can actually turn on a particular kind of memory just by activating a particular set of neurons that was active during an experience, right? So... There's a lot of conservation of some of these neural circuits across evolution in mammals, for instance.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then some people would even say that there's genetic mechanisms for learning that are conserved even going back far, far before evolution. But let's go back to the mice and humans question. There's a lot of differences. So for one thing, the sensory information is very different.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Mice and rats explore the world largely through smelling, olfaction, but they also have vision that's designed to catch death from above. So it's like a very big view of the world. And we move our eyes around in a way that focuses on particular spots in space where you get very high resolution from a very limited set of spots in space. So that makes us very different in that way.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
We also have all these other structures as social animals that allow us to respond differently. There's language. So you name it, there's obviously gobs of differences. Humans aren't just giant rats. There's a bunch more complexity to us. Time scales are very important.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So primate brains and human brains are especially good at integrating and holding on to information across longer and longer periods of time, right? And also, you know, finally, it's like our history of training data, so to speak, is very, very different than, you know, I mean, a human's world is very different than a wild mouse's world.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Danny really impacted me because I was an undergrad at Berkeley, and I got to take a class from him long before he won the Nobel Prize or anything, and it was just a mind-blowing class. But this idea of the remembering self and the experiencing self, I got into it because it's so much about memory, even though he doesn't study memory. So we're right now having this experience, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And a lab mouse's world is extraordinarily impoverished relative to an adult human.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, yes, but that's very important, right? So you can understand, for instance, how do neurons talk to each other? That's a really big, big question. Neural computation, you'd think it's the most simple question, right? Not at all. I mean, it's a big, big question. And understanding how two parts of the brain interact, meaning that it's not just one area speaking.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's not like Twitter where one area of the brain is shouting and then another area of the brain is just stuck listening to this crap. It's like they're actually interacting on the millisecond scale, right? How does that happen? And how do you regulate those interactions, these dynamic interactions? interactions.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
We're still figuring that out, but that's going to be coming largely from model systems that are easier to understand. You can do manipulations like drug manipulations to manipulate circuits and use viruses and so forth and lasers to turn on circuits that you just can't do in humans. So I think there's a lot that can be learned from mice. There's a lot that can be learned from non-human primates.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then there's a lot that you need to learn from humans. And I think, unfortunately, some of the people in the National Institutes of Health think you can learn everything from the mouse. It's like, why study memory in humans when I could study learning in a mouse? And just like, oh my God, I'm going to get my funding from somewhere else.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So deja vu is, it's actually one of these things I think that some of the surveys suggest that like 75% of people report having a deja vu experience one time or another. I don't know where that came from, but I've polled people in my class and most of them say they've experienced deja vu. It's this kind of sense that I've experienced this moment sometime before, I've been here before.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And actually, there's all sorts of variants of this. The French have all sorts of names for various versions of the chamivou, parleyvou, I don't know. All these different vous. But déjà vu is the sense that it can be an almost disturbing intense sense of familiarity. So there is a researcher named Wilder Penfield. Actually, this goes back even earlier to some of the earliest
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Hughlings Jackson was this neurologist who did a lot of the early characterizations of epilepsy. And one of the things he notices in epilepsy patients, some group of them, right before they would get a seizure, they would have this intense sense of deja vu. So it's this artificial sense of familiarity. It's a sense of having a memory that's not there, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so what was happening was there was electrical activity in certain parts of these brains. And so this guy Penfield later on, when he was trying to look for how do we map out the brain to figure out which parts we want to remove and which parts don't we, he he would stimulate parts of the temporal lobes of the brain and find you could elicit the sense of deja vu.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Sometimes you'd actually get a memory that a person would re-experience just from electrically stimulating some parts. Sometimes they just have this intense feeling of being somewhere before. And so one theory which I really like is is that in higher order areas of the brain, they're integrating for many, many different sources of input.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And people can watch it presumably on YouTube or listen to it on audio. But if you're talking to somebody else, you could probably describe this whole thing in 10 minutes. But that's going to miss a lot of what actually happened. And so the idea there is that the way we remember things is not the replay of the experience. It's something totally different.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
What happens is is that they're tuning themselves up every time you process a similar input, right? And so, that allows you to just get this kind of a fluent sense that I'm very familiar. You're very familiar with this place, right? And so just being here, you're not going to be moving your eyes all over the place because you kind of have an idea of where everything is.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And that fluency gives you a sense of like, I'm here. Now I wake up in my hotel room and I have this very unfamiliar sense of where I am, right? But there's a great set of studies done by Ann Cleary at Colorado State where she created these virtual reality environments. And we'll go back to the metaverse. Imagine you go through a virtual museum, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And then she would put people in virtual reality and have them go through a virtual arcade. Mm-hmm. But the map of the two places was exactly the same. She just put different skins on them. So one looks different than the other, but they've got same landmarks and same places, same objects and everything, but carpeting, colors, theme, everything's different.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
People will often not have any conscious idea that the two are the same, but they could report this very intense sense of deja vu. So it's like a partial match that's eliciting this kind of a sense of familiarity. And, and that's why, you know, in patients who have epilepsy that affects memory, you get this artificial sense of familiarity that happens.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so we think that, and again, this is just one theory amongst many, but we think that's, we get a little bit of that feeling. It's not enough to necessarily give you deja vu. even for very mundane things, right? So it's like if I tell you the word rutabaga, your brain's gonna work a little bit harder to catch it than if I give you a word like apple, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And that's because you hear apple a lot. So your brain's very tuned up to process it efficiently, but rutabaga takes a little bit longer and more intense. And you can actually see a difference in brain activity in areas in the temporal lobe when you hear a word just based on how frequent it is in the English language.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So we think it's tied to this basic, it's basically a byproduct of our mechanism of just learning, doing this error-driven learning as we go through life to become better and better and better to process things more and more efficiently.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, it doesn't happen all the time, but I think what may be happening is it's a partial match to something that we have, and it's not enough to trigger that sense of that ability to pull together all the pieces, but it's a close enough match to give you that intense sense of familiarity without the recollection of exactly what happened when.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it tends to be biased by the beginning and the end. And he talks about the peaks, but there's also the best parts, the worst parts, et cetera. And those are the things that we remember. And so when we make decisions, we usually consult memory and we feel like our memory is a record of what we've experienced, but it's not.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, I like to say there's no such thing as true or false memories, right? It's like Johnny Rotten from the Sex Pistols, he had a saying that's like, I don't believe in false memories any more than I believe in false songs, right? And so the basic idea is that we have these memories that reflect bits and pieces of what happened as well as our inferences and theories, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So I'm a scientist and I collect data, but I use theories to make sense of that data. And so a memory is kind of a mix of all these things.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So where memories can go off the deep end and become what we would call conventionally as false memories are sometimes little distortions where we filled in the blanks, the gaps in our memory based on things that we know but don't actually correspond to what happened, right? Mm-hmm.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So, if I were to tell you that I'm, like, you know, a story about this person who's, like, worried that they have cancer or something like that, and then, you know, they see a doctor and the doctor says, well, things are very much like you would have expected or, like, you know, what you were afraid of or something.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
When people remember that, they'll often remember, well, the doctor told the patient that he had cancer, even if that wasn't in the story, because they're infusing meaning into that story, right? So that's a minor distortion.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But what happens is that sometimes things can really get out of hand where people have trouble telling the difference in things that they've imagined versus things that happen. But also, as I told you, the act of remembering can change the memory, right? And so what happens then is you can actually be exposed to some misinformation. And so Elizabeth Loftus was a real pioneer in this work.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And there's lots of other work that's been done since. But basically, it's like if you remember some event and then I tell you something about the event. Later on, when you remember the event, you might remember some original information from the event as well as some information about what I told you.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And sometimes if you're not able to tell the difference, that information that I told you gets mixed into the story that you had originally. So now I give you some more misinformation or you're exposed to some more information somewhere else. And eventually your memory becomes totally detached from what happened.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so sometimes you can have cases where people—this is very rare, but you can do it in the lab, too, where a significant—not everybody, but a chunk of people will fall for this—where you can give people—
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
misinformation about an event that never took place and as they keep trying to remember that event more and more what happens they start to imagine they start to pull up things from other experiences they've had and eventually they can stitch together a vivid memory of something that never happened because they're not remembering an event that happened they're remembering the act of trying to remember what happened and basically putting it together into the wrong story
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, absolutely. I mean, this is exactly what they do. And so all these kind of foibles of human memory get magnified when you start to have social interactions. There's a whole literature on something called social contagion, which is basically when misinformation spreads like a virus. Like, you remember the same thing that I did, but I give you a little bit of wrong information.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's this kind of very biased sample, but it's biased in an interesting and I think biologically relevant way.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Then that becomes part of your story of what happened. Because once you and I share a memory... Like I tell you about something I've experienced and you tell me about your experience of the same event. It's no longer your memory or my memory. It's our memory. And so now the misinformation spreads.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And the more you trust someone or the more powerful that person is, the more of a voice they have in shaping that narrative. Right. And there's all sorts of interesting ways in which misinformation can happen. There's a great example of when John McCain and George Bush Jr.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
were in a primary, and there were these polls where they would do these—I guess they were not robocalls but real calls—where they would poll voters. But they actually inserted some misinformation about McCain's beliefs on taxation, I think, and maybe it was something about illegitimate children. I don't really remember.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But they included misinformation in the question that they asked, like, how do you feel about the fact that he wants to do this or something? And so people would end up becoming convinced he had these policy things or these personal things that were not true, just based on the polls that were being used.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So it was a case where, interestingly enough, the people who were using misinformation were actually ahead of the curve relative to the scientists who were trying to study these effects in memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Basically, I think that a lot of learning in the brain is driven towards being able to make sense. I mean, really, memory is all about the present and the future. The past is done, so biologically speaking, it's not important unless there's something from the past that's useful.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, I mean, there's so much in what you're saying. I mean, one of the things is that people's sense of collective identity is very much tied to shared memories. If we have a shared narrative of the past, or even better, if we have a shared past, we will feel more socially connected with each other, and I will feel part of this group. They're part of my tribe if I remember the same things.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
in the same way. And you brought up this weaponization of history. And it really speaks to, I think, one of the parts of memory, which is that if you have a belief and you have a goal in mind, you will find stuff in memory that aligns with it, and you won't see the parts in memory that don't. So a lot of the stories we put together are based on our perspectives.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so let's just zoom out for the moment from misinformation, take something even more fascinating, but not as scary. I was reading Thanh Viet Nguyen, but he wrote a book about the collective memory of the Vietnam War. He's a Vietnamese immigrant who was flown out after the war was over. And so he went back to his family to get their stories about the war.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And they called it the American War, not the Vietnam War, right? And that just kind of blew my mind, having grown up in the U.S., and I've always heard about it as the Vietnam War. But of course they call it the American War, because that's what happened. America came in, right? And that's based on their perspective, which is a very valid perspective.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so that just gives you this idea of the way we put together these narratives based on our perspectives. And I think the opportunities that we can have in memory is if we bring groups together from different perspectives and we allow them to talk to each other and we allow ourselves to listen.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, right now you'll hear a lot of just jammering, you know, people going blah, blah, blah about free speech, but they just want to listen to themselves, right? Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
it's like let's face it the old days before people were supposedly woke they were trying to ban two live crew or you know just think about letty bruce got canceled for cursing jesus christ you know it's like this is nothing new yeah people don't like to hear things that disagree with them but um I mean, you can see two situations in groups with memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
One situation is you have people who are very dominant, who just take over the conversation. And basically what happens is the group remembers less from the experience, and they remember more of what the dominant narrator says, right? Mm-hmm. Now, if you have a diverse group of people, and I don't mean diverse in necessarily the human resources sense of the word.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so what our brains are really optimized for is to learn about the stuff from the past that's going to be most useful in understanding the present and predicting the future, right? And so cause-effect relationships, for instance, that's a big one. Now, my future is completely unpredictable in the sense that you could, in the next 10 minutes, pull a knife on me and slit my throat, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, diverse in any way you want to take it, right? But diverse in every way, hopefully. And you give everyone a chance to speak and everyone's being appreciated for their unique contribution. You get more accurate memories and you get more information from it, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Even to people who come from very similar backgrounds, if you can appreciate the unique contributions that each one has, you can do a better job of generating information from memory. And that's a way to inoculate ourselves, I believe, from misinformation in the modern world. But like everything else, it requires a certain tolerance for discomfort.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think when we don't have much time and I think when we're stressed out and when we are just tired, it's very hard to tolerate discomfort.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, and that's the human problem. I think a lot of the problems that come up with technology aren't the technology itself as much as the fact that people adapt to the technology in maladaptive ways. I mean, one of my fears about AI is not what AI will do, but what people will do. I mean, take text messaging, right? It's a pain in the ass to text people, at least for me.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so what happens is the communication becomes very Spartan and devoid of meaning, right? And it's just very telegraphic. And that's people adapting to the medium, right? I mean, look at you. You've got this keyboard, right? That's got these dome-shaped things. And you've adapted to that to communicate, right? That's not the technology adapting to you. That's you adapting to the technology.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think one of the things I learned when Google started to introduce autocomplete in emails, I started to use it and about a third of the time I was like, this isn't what I wanna say. A third of the time I'd be like, this is exactly what I wanted to say. And a third of the time I was saying, well, this is good enough, I'll just go with it, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so what happens is it's not that the technology necessarily is doing anything so bad as much as it's just going to constrain my language because I'm just doing what's being suggested to me. And so this is why I say, you know, kind of like my mantra for some of what I've learned about everything in memory is to diversify your training data, basically.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Because otherwise you're going to, so like humans have this capability to be so much more creative than anything generative AI will put together, at least right now, who knows where this goes.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But it can also go the opposite direction where people could become much, much less creative if they just become more and more like resistant to discomfort, you know, and resistant to exposing themselves to novelty, to cognitive dissonance and so forth.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I was planning on it. Exactly. But having seen some of your work, generally my expectations about life, I'm not expecting that. I have a certainty that everything's going to be fine. We're going to have a great time talking today, right? But we're often right. It's like, okay, so I go to see a band on stage. I know they're going to make me wait. The show's going to start late. They come on.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But I don't know necessarily that tracks people's happiness, right? I mean, I would argue that maybe, who knows? I don't know this, but I wouldn't be surprised if people in hunter-gatherer societies were I mean, I wouldn't be surprised if they're happier than people who have access to modern medicine and email and cell phones.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Or maybe cultural connection. Maybe it's about functioning in social groups that are meaningful and having time. But I do think there's an interesting memory-related thing, which is that if you look at things like reinforcement learning, for instance, you're not learning necessarily... Every time you get a reward, if it's the same reward, you're not learning that much.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You mainly learn if it deviates from your expectation of what you're supposed to get, right? So it's like you get a paycheck every month from MIT or whatever, right? And it's like you probably don't even kind of get excited about it when you get the paycheck. But if they cut your salary, you're going to be pissed. And if they increase your salary, you're like, oh, good, I got a bonus, you know?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And that adaptation and that ability that basically you learn to expect these things, I think, is a major source of, I guess, it's a major way in which we're kind of more, in my opinion, wired to strive and not be happy together. to be in a state of wanting. And, you know, some people talk about dopamine, for instance, being this pleasure chemical.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
There's a very good chance there's going to be an encore onstage. I have a memory, so to speak, for that event before I've even walked into the show, right? There's going to be people holding up their camera phones to try to take videos of it now because this is kind of the world we live in. So that's like everyday fortune-telling that we do, though. It's not... real, it's imagined.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it's like, there's a lot of compelling research to suggest it's not about pleasure at all. It's about the discomfort that energizes you to get things, to seek a reward, right? And so you could give an animal that's been deprived of dopamine a reward and enjoy it. It's pretty good. But they're not going to do anything to get it, you know.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And just one of the weird things in our research is I got into curiosity from a postdoc in my lab, Matthias Gruber. And one of the things that we found is when we gave people a question, like a trivia question that they wanted the answer to, The question, the more curious people were about the answer, the more activity in these dopamine-related circuits in the brain we would see.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And again, that was not driven by the answer per se, but by the question. So it was not about getting the information, it was about the drive to seek the information. But it depends on how you take that.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
If you get this uncomfortable gap between what you know and what you want to know, you could either use that to motivate you and energize you, or you could use it to say, I don't want to hear about this. This disagrees with my beliefs. I'm going to go back to my echo chamber. Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
That's like a hardcore band name. Yeah, yeah, yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I also like the Hedonic Treadmill.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, yeah. We could use that for like our techno project, I think.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
We could build a false memory of a show, in fact, if you want. Let's just put it all together. We don't even have to do all the work to play the show. We can just create a memory of it. It might as well happen because the remembering self is in charge anyway.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, I mean, I think there's a lot of history of this, actually, in the criminal justice system. You might have heard the term the third degree. If you actually look it up, historically, it was a very intense situation. set of beatings and, you know, starvation and physical demands that they would place on people to get them to talk.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And, you know, there was certainly a lot of work in the, that's been done by the CIA in terms of enhanced interrogation techniques. And from what I understand, the research actually shows that they just produce what people want to hear, not necessarily the information that is being looked for. And the reason is, is that, you know, I mean, there's different reasons.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And it's amazing that we have this capability, and that's what memory is about. But it can also give us this illusion that we know everything that's about to happen. And I think what's valuable about that illusion is when it's broken, it gives us the information, right? I'm sure being an AI, you know about information theory, and the idea is the information is what you didn't already have.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, one is people just get tired of being tortured and just say whatever. But another part of it is that you create a very interesting set of conditions where there's an authority figure telling you something that you did this. We know you did this. We have witnesses saying you did this. So now you start to question yourself. Then they put you under stress. Maybe they're not feeding you.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Maybe they're kind of like making you be cold or, you know, exposing you to like music that you can't stand or something, whatever it is, right? It's like they're creating this physical stress. And so stress starts to act on, you know, starts to downregulate the prefrontal cortex. You're not necessarily as good at monitoring the accuracy of stuff.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Then they start to get nice to you and they say, imagine, you know, okay, I know you don't remember this, but maybe we can walk you through how it could have happened. And they feed you the information. And so you're in this weakened mental state and you're being encouraged to imagine things by people who give you a plausible scenario.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And at some point, certain people can be very coaxed into creating a memory for something that never happened. Yeah. And there's actually some pretty convincing cases out there where you don't know exactly the truth. There's a sheriff, for instance, who came to believe that he had a false memory. I mean, that he had a memory of doing sexual abuse based on, you know, essentially, I think it was...
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You know, I'm not going to tell the story because I don't remember it well enough to necessarily accurately give it to you, but people could look this stuff up. There are definitely stories out there like this where people confess to crimes that they just didn't do and objective evidence came out later on.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But there's a basic recipe for it, which is you feed people the information that you want them to remember. You stress them out. You have an authority figure kind of like pushing this information on them. Or you motivate them to produce the information you're looking for, and that pretty much over time gives you what you want.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Oh, God, that's so hard to... Asking for a friend, I love that. Oh, it's such a hard one. Well, so, I mean, part of this is... We tend to go back to particular times that are the more emotionally intense periods, and so that's a part of it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And again, memory is designed to kind of capture these things that are biologically significant, and attachment is a big part of biological significance for humans, human relationships. are super important.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And sometimes that heartbreak comes with massive changes in your beliefs about somebody, say they cheated on you or something like that, or regrets and you kind of ruminate about things that you've done wrong.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
there's really so many reasons though, but you know, I mean, I, I've had this, I, um, uh, my first pet I had as, you know, was, we got it for a wedding present as a cat and got it after like, uh, but it died of FIP when it was four years old. And, you know, I just would see her everywhere around the house.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You know, we got another cat that we got a dog, dog eventually died of cancer and the cat just died recently. Um, And, you know, so we got a new dog because I kept seeing the dog around and I was just so heartbroken about this. But I still remember the pets that died. It just comes back to you. I mean, it's part of this.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so those prediction errors that we make based on, you know, we make a prediction based on memory and the errors are where the action is.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I think there's also something about attachment that's just so crucial that drives, again, these things that we want to remember and that gives us that longing sometimes. Sometimes it's also not just about the heartbreak. but about the positive aspects of it, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Because the loss comes from not only the fact that the relationship is over, but you had all of these good things before that you can now see in a new light, right? And so one of the things that I found from my clinical background that really, I think, gave me a different perspective on memory is so much of the therapy process was guided towards reframing
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
and getting people to look at the past in a different way, not by imposing, changing people's memories or not by imposing an interpretation, but just offering a different perspective and maybe one that's kind of more optimized towards learning and appreciation maybe or gratitude, whatever it is, right? That gives you a way of taking, I think you said it in the beginning, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Where you can have this kind of like dark experiences and you can use it as training data to, you know, grow in new ways, but it's hard. Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Exactly, exactly.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So you don't believe that an owner of a lonely heart is much better than an owner of a broken heart? You think an owner of a broken heart is better than the owner of a lonely heart?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, you know, it's funny because it's like after I turned 50, I think of death all the time. Like, I just think that, you know, I'm in like, I probably, I have fewer, probably a fewer years ahead of me than I have behind me. Right. So you think about, I think about one thing, which is what are the memories that I want to carry with me for the next period of time.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And also about like, just the fact that everything around me could be, you know, I know more people who are, you dying for various reasons. I'm not lots, I'm not that old, right? But it's something I think about a lot, and I'm reminded of how I talked to somebody who's a Buddhist, and I was like, the whole idea of Buddhism is renouncing attachments.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
In some way, the idea of Buddhism is staying out of the world of memory and staying in the moment, right? And And they talked about, you know, it's like, how do you renounce attachments to the people that you love, right? And they're just saying, well, I appreciate that I have this moment with them and knowing that they will die makes me appreciate this moment that much more.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I mean, you said something similar, right, in your daily routine that you think about things this way, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, you know, this is where Hinduism and Buddhism, or at least some strains of Hinduism and Buddhism, differ. In Hinduism, like if you read the Bhagavad Gita, the philosophy is not one of renouncing the world, because the idea is that not doing something is no different than doing something, right? So what they argue—and again, you could interpret it in different ways, positive and negative—
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But the argument is, is that you don't want to renounce action, but you want to renounce the fruits of the action. You don't do it because of the outcome. You do it because of the process, because the process is part of the balance of the world that you're trying to preserve. Right. And of course, you could take that different ways.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But I really think about that from time to time in terms of like, you know. letting go of this idea of does this book sell or trying to impress you and get you to laugh at my jokes or whatever and just be more like I'm sharing this information with you and getting to know you or whatever it is. But it's hard, right? Because we're so driven by the reinforcer, the outcome.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yep, it's my thermo.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah. And the reason is, is that in some sense, I think, especially the farther we go back, I mean, there's all sorts of interesting things that happen. So your sense of like, if I ask you, how different does one hour ago feel from two hours ago, you'd probably say pretty different. But if I ask you, okay, go back one year ago versus one year and one hour ago, it's the same difference in time.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It won't feel very different, right? So there's this kind of compression that happens as you look back farther in time. So it's kind of like why when you're older, the difference between somebody who's like 50 and, you know, 45 doesn't seem as big as the difference between like 10 and five or something, right? When you're 10 years old, everything seems like it's a long period of time.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Here's the point is that, you know, so one of the interesting things that I found while I was working on the book actually was during the pandemic, I just decided to ask people in my class when we were doing the remote instruction. So one of the things I did was I would poll people. And so I just asked people, do you feel like the days are moving by slower or faster or about the same? Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Almost everyone in the class said that the days were moving by slower. So then I would say, okay, so do you feel like the weeks are passing by slower, faster, or the same? And the majority of them said that the weeks were passing by faster. So according to the laws of physics, I don't think that makes any sense, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But according to memory, it did, because what happened was people were doing the same thing over and over in the same context. And without that change in context, their feeling was that they were in one long, monotonous event. Right. And so but then at the end of the week, you look back at that week and you say, well, what happened? No memories of what happened.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So it must that week just went by without even my noticing it. But that week went by during the same amount of time as an eventful week where you might have been going out, hanging out with friends on vacation or whatever. Right. It's just that nothing happened because you're doing the same thing over and over. So I feel like memory really shapes our sense of time.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But it does so in part because context is so important for memory.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Like you don't feel the passage of time or?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Maybe what it is is that you really like to see connections between things. This is like really what motivates me in science actually too. But it's like when you start recalling the past to, you know, and seeing the connections between the past and present,
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
now you have this kind of web of interconnected memories right and so i can imagine in that sense there is this kind of the present is with you right um but what's interesting about what you said too that struck me is that your 16 year old self was probably very complex you know and i'm by the way i'm the same way but it's like it really is the source of a lot of dark for me.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Okay. Well, first I'll say, I wish I could take you on the road with me because that was such a great description. Can I be your opening act? Oh my God. No, I'm going to open for you, dude. Otherwise it's like, you know, everybody leaves after you're done. Believe me, I did that in Columbus, Ohio once. It wasn't fun. The opening acts drank our bar tab.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But when you can look back at, let's say you hear a song that you used to play before you would go do a sports thing or something like that, and you might not think of yourself as an athlete, but once you get back to that, you mentally time travel to that particular thing, you open up this little compartment of yourself that wasn't there before, right? That didn't seem accessible for us.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Dan Schachter's lab did this really cool study where they would ask people to either remember doing something altruistic or imagine doing something altruistic. And that act made them more likely to want to do things for other people. So that act of mental time travel can change who you are in the present.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And we tend to think of, this goes back to that illusion of stability, and we tend to think of Memory in this very deterministic way that I am who I am because I have this past. But we have a very multifaceted past and can access different parts of it and change in the moment based on whatever part we want to reach for, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, so my friend Philippe de Brigarde wrote this, and it just blew my mind, where the word nostalgia was coined by a Swiss physician who was actually studying traumatized soldiers. And so he described nostalgia as a disease. And the idea was it was bringing these people extraordinary unhappiness because they're remembering how things used to be. And I think it's very complex.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So as people get older, for instance, nostalgia can be an enormous source of happiness, right? And being nostalgic can improve people's moods in the moment. But it just depends on what they do with it, because what you can sometimes see is nostalgia has the opposite effect of thinking those were the good old days and those days are over. Right.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
It's like America used to be so great and now it sucks. You know, my life used to be so great when I was a kid and now it's not. Right. And you're selectively remembering the things that we don't realize how selective our remembering self is. And so, you know, I lived through the 70s. It sucked.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Partly it sucked more for me, but I would say that even otherwise, it's like there's all sorts of problems going on. Gas lines, people were like, you know, worried about like Russia, nuclear war, blah, blah, blah. So, I mean, it's just this idea that people have about the past can be very useful to
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
If it brings you happiness in the present, but if it narrows your worldview in the present, you're not aware of those biases that you have, it can be toxic, either at a personal level or at a collective level.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
We spent all this money going all the way there. Everybody left after the opening acts were done, and there was just that stoner dude with the dreadlocks hanging out. And then next thing you know, we blew our savings on getting a hotel room.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Yeah, I mean, I can't say specifics about the company because I haven't studied it that much. But I mean, I think there's two parts of it. So one is they're developing some really interesting technology, I think, with these like surgical robots and things like that. BCI, though, has like a whole lot of innovation going on.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I'm not necessarily seeing any scientific evidence from Neuralink, and maybe that's just because I'm not looking for it, but I'm not seeing the evidence that they're anywhere near where the scientific community is. And there's lots of startups that are doing incredibly innovative stuff. One of my colleagues, Sergey Savitsky, is just like a genius in this area, and they're working on it.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I think speech... Prosthetics that are incorporating decoding techniques with AI and movement prosthetics. The rate of progress is just enormous. So part of the technology is having good enough data and understanding which data to use and what to do with it, right? Mm-hmm. And then the other part of it then is the algorithms for decoding it and so forth.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And I think part of that has really resulted in some real breakthroughs in neuroscience as a result. So there's lots of new technologies like Neuropixels, for instance, that allow you to harvest activity from many, many neurons from a single electrode. I know Neuralink has some technologies that are also along these lines, but I haven't, again, because they do their own stuff.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
The scientific community doesn't see it, right? But I think BCI is much, much bigger than Neuralink, and there's just so much innovation happening. I think the interesting question, which we may be getting into, is I was talking to Sergey a while ago about, you know, so a lot of language is not just what we hear and what we speak. but also our intentions and our internal models.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
And so are you really going to be able to restore language without dealing with that part of it? And he brought up a really interesting question, which is the ethics of reading out people's intentions and understanding of the world as opposed to the more concrete parts of hearing and producing movements, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
When I was in grad school, I played in a band and yeah, we traveled, we would play shows. It wasn't like we were in a hardcore touring band, but we did some touring and had some fun times. And yeah, we did a movie soundtrack. Nice. Henry Portrait of a Serial Killer. So that's a good movie. We were on the soundtrack for the sequel, Henry II, Mask of Sanity, which is a terrible movie. Yeah.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, I mean, in some sense, we know we can do it just behaviorally, right?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
I can just tell you, under certain conditions anyway, I can give you the misinformation, and then you can change the people and places and so forth, right? On the crude level, there's a lot of work that's being done on a phenomenon called reconsolidation, which is the idea that essentially when I recall a memory—
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
what happens is that the connections between the neurons and that cell assembly that give you the memory are going to be more modifiable. And so some people have used techniques to try to, for instance, with fear memories, to reduce that physical visceral component of the memory when it's being activated.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Right now, I think I've, as an outsider looking at the data, I think it's like mixed results. And part of it is, and this speaks to the more complex issue, is that you need somebody to actually fully recall that traumatic memory in the first place. And in order to actually modify it, then what is the memory? That is the key part of the problem.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So if we go back to reading people's thoughts, what is the thought? I mean, people can sometimes look at this like behaviorists and go, well, the memory is like I've given you A and you produce B. And I think that's a very bankrupt concept about memory. I think it's much more complicated than that. And one of the things that when we started studying naturalistic memory, like memory from movies,
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
How's the soundtrack?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
that was so hard was we had to change the way we did the studies because if i show you a movie and i show and i watch the same movie and you recall everything that happened and i recall everything that happened we might take a different amount of time to do it we might use different words and yet to an outside observer we might have recalled the same thing right
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
At least that one part where the guy throws up the milkshake. Okay, all right.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
So it's not about the words necessarily, and it's not about how long we spent or whatever. There's something deeper that is there that's this idea, but it's like, how do you understand that thought? I encounter a lot of concrete thinking that it's like, if I show... a model like the visual information that a person sees when they drive, I can basically reverse engineer driving.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Well, that's not really how it works. I once saw a talk by somebody, or I saw somebody talking in this discussion between neuroscientists and AI people, and he was saying that the problem with self-driving cars that they had in cities as opposed to highways was that the car was okay at doing the things it's supposed to,
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
But when there were pedestrians around, it couldn't predict the intentions of people. And so that unpredictability of people was the problem that they were having in, you know, the self-driving car design because it didn't have a good enough internal model of what the people were, you know, what they were doing, what they wanted. And what do you think about that?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
All right, we're getting back to life advice.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
One thing that I try to live by, especially nowadays, and since I wrote the book, I've been thinking more and more about this, is... How do I want to live a memorable life? You know, I think if we go back to like the pandemic, right, how many people have memories from that period, aside from the trauma of being, you know, locked up and seeing people die and.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
You think an LLM is building that world model?
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
there's a million things i could say but like one of them determining who around you is an asshole aggressive driver yes i was just thinking about this yeah or like you can read it a mile once you get become a great driver you can see it a mile away this guy is gonna pull an asshole move in front of you exactly It's like way back there, but you know it's going to happen.
Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
all this stuff um i think it's like one of these things where we were stuck inside looking at screens all day doing the same thing with the same people and so i don't remember much from that in terms of those good memories that you're talking about right You know, when I was growing up, my parents worked really hard for us and, you know, we went on some vacations, but not very often.