Lex Fridman Podcast
#430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories
Sat, 25 May 2024
Charan Ranganath is a psychologist and neuroscientist at UC Davis, specializing in human memory. He is the author of a new book titled Why We Remember. Please support this podcast by checking out our sponsors: - Riverside: https://creators.riverside.fm/LEX and use code LEX to get 30% off - ZipRecruiter: https://ziprecruiter.com/lex - Notion: https://notion.com/lex - MasterClass: https://masterclass.com/lexpod to get 15% off - Shopify: https://shopify.com/lex to get $1 per month trial - LMNT: https://drinkLMNT.com/lex to get free sample pack Transcript: https://lexfridman.com/charan-ranganath-transcript EPISODE LINKS: Charan's X: https://x.com/CharanRanganath Charan's Instagram: https://instagram.com/thememorydoc Charan's Website: https://charanranganath.com Why We Remember (book): https://amzn.to/3WzUF6x Charan's Google Scholar: https://scholar.google.com/citations?user=ptWkt1wAAAAJ Dynamic Memory Lab: https://dml.ucdavis.edu/ PODCAST INFO: Podcast website: https://lexfridman.com/podcast Apple Podcasts: https://apple.co/2lwqZIr Spotify: https://spoti.fi/2nEwCF8 RSS: https://lexfridman.com/feed/podcast/ YouTube Full Episodes: https://youtube.com/lexfridman YouTube Clips: https://youtube.com/lexclips SUPPORT & CONNECT: - Check out the sponsors above, it's the best way to support this podcast - Support on Patreon: https://www.patreon.com/lexfridman - Twitter: https://twitter.com/lexfridman - Instagram: https://www.instagram.com/lexfridman - LinkedIn: https://www.linkedin.com/in/lexfridman - Facebook: https://www.facebook.com/lexfridman - Medium: https://medium.com/@lexfridman OUTLINE: Here's the timestamps for the episode. On some podcast players you should be able to click the timestamp to jump to that time. (00:00) - Introduction (10:18) - Experiencing self vs remembering self (23:59) - Creating memories (33:31) - Why we forget (41:08) - Training memory (51:37) - Memory hacks (1:03:26) - Imagination vs memory (1:12:44) - Memory competitions (1:22:33) - Science of memory (1:37:48) - Discoveries (1:48:52) - Deja vu (1:54:09) - False memories (2:14:14) - False confessions (2:18:00) - Heartbreak (2:25:34) - Nature of time (2:33:15) - Brain–computer interface (BCI) (2:47:19) - AI and memory (2:57:33) - ADHD (3:04:30) - Music (3:14:15) - Human mind
The following is a conversation with Charan Ranganath, a psychologist and neuroscientist at UC Davis, specializing in human memory. He's the author of Why We Remember, Unlocking Memory's Power to Hold on to What Matters. And now a quick few second mention of each sponsor. Check them out in the description. It's the best way to support this podcast.
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Danny Kahneman describes the experiencing self and the remembering self, and that happiness and satisfaction you gain from the outcomes of your decisions do not come from what you've experienced, but rather from what you remember of the experience. So can you speak to this interesting difference that you write about in your book of the experiencing self and the remembering self?
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?
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.
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.
It's this kind of very biased sample, but it's biased in an interesting and I think biologically relevant way.
So in the way we construct a narrative about our past, you say that it gives us an illusion of stability. Can you explain that?
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.
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?
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.
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.
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.
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.
The error is where the learning happens.
Exactly, exactly.
Well, just to linger on Danny Kahneman and just this whole idea of experiencing self versus remembering self, I was hoping you can give a simple answer of how we should live life.
based on the fact that our memories could be a source of happiness or could be the primary source of happiness, that an event, when experienced, bears its fruits the most when it's remembered over and over and over and over. And maybe there is some wisdom in the fact that we can control to some degree how we remember it.
how we evolve our memory of it such that it can maximize the long-term happiness of that repeated experience.
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.
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.
So as a small tangent, you're a legit touring act.
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.
How's the soundtrack?
It's pretty good. It's badass.
At least that one part where the guy throws up the milkshake. Okay, all right.
Which is my song. We're going to have to see. We're going to have to see it.
All right, we're getting back to life advice.
And happiness, yeah.
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.
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.
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.
But the remembering self will be like, yes, I'm so glad I did that.
Do things that are very unpleasant in the moment because those can be reframed and enjoyed for many years to come. That's probably good advice, or at least when you're going through shit, it's a good way to see the silver lining of it.
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...
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.
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.
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.
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.
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.
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.
Well, actually, just for me, you're making me realize now that it's not just those kinds of stories, but even things like periods of depression or really low points. To me, at least, it feels like a motivating thing that... The darker it gets, the better the story will be if you emerge on the other side. That, to me, feels like a motivating thing.
So maybe if people are listening to this and they're going through some shit, as we said, one thing that could be a source of light is that it'll be a hell of a good story when it's all over, when you emerge on the other side. Let me ask you about decisions.
You've already talked about it a little bit, but when we face the world and we're making different decisions, how much does our memory come into play? Is it the kind of narratives that we've constructed about the world that are used to make predictions that's fundamentally part of the decision-making?
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.
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.
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
overcome or things that we build on in a positive way. But either way, they define us.
And probably the earlier in life the memories happen, the more defining power they have in terms of determining who we become.
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.
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.
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?
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.
Is there some insight into the human brain that explains why we don't seem to remember anything from the first few years of life?
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.
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.
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.
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
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.
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.
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.
Well, I think somebody once said to me that kind of loosely, philosophically, that the reason we don't remember the first few years of life, infantile amnesia, is because how traumatic it is. Basically, the error rate that you mentioned when... Your brain's prediction doesn't match reality. The error rate in the first few years of life, your first few months certainly, is probably crazy high.
It's just nonstop freaking out. The collision between your model of the world and how the world works is just so high that you want whatever the trauma of that is not to linger around. I always thought that's an interesting idea because just imagine the insanity of what's happening in a human brain in the first couple of years. You don't know anything.
And there's just this stream of knowledge and we're somehow, given how plastic everything is, it just kind of molds and figures it out. But it's like an insane waterfall of information.
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?
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.
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.
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.
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.
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.
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.
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.
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?
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?
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.
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.
So it is always optimal in a sense. Yeah. Just optimal for that stage of life.
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.
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.
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.
Well, it's just fascinating to think of the individual orca or human throughout his life in stages doing a kind of optimal wisdom development.
so in the early days you don't even know what the goal is and you figure out the goal and you kind of optimize for that goal and you pursue that goal and then all the wisdom you collect through that then you share with the others in the system with the other individuals and as a as a collective then you kind of converge towards greater wisdom throughout the generation so in that sense it's optimal us humans and orcas got something going on it works apex predators
uh i just got a megalodon tooth speaking of apex partners it's uh just imagine the size of that thing anyway uh how does the brain forget and how and why does it remember so maybe some of the mechanisms you mentioned the hippocampus what are the different components involved here
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
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.
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.
And in fact, you could extract entirely new memories depending on how you feed
You have to have the right query, the right prompt to access that, whatever the part you're looking for.
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.
So that's a big part of it too, is just this kind of what we call retrieval failure.
You mentioned episodic memory, you mentioned semantic memory. What are the different separations here? What's working memory, short-term memory, long-term memory? What are the interesting categories of memory?
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.
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.
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.
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.
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.
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.
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.
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.
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.
So if you have something like a birthday party and you've been to many before, you're going to load that from disk into working memory, this model, and then you're mostly operating on the model. And if it's a new... task you're you don't have a model so you're more in the data collection yes one of the fascinating things that we've been studying and
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.
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.
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.
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.
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
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.
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.
Can memory be trained and improved? This beautiful connected system that you've described, what aspect of it is a mechanism that can be improved through training?
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.
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?
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,
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?
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.
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.
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.
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
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.
The implication there is that attention is a fundamental component of remembering something, allocating attention to it. And then attention might be something that you could train. How you allocate attention and how you hold attention on a thing.
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
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.
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.
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.
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?
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?
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.
There's certain hacks. There's something called the memory palace that I've played with. I don't know if you're familiar with that whole technique. And it works. Yeah. It's interesting. So another thing I recommend for people a lot is I use Anki a lot every day. It's an app that does spaced repetition. So I think medical students and students use this a lot to remember a lot of different things.
Oh, yeah. Okay, we can come back to this. But yeah, go on.
Sure. It's the whole concept of spaced repetition. When the thing is fresh, you kind of have to remind yourself of it a lot. And then over time, you can... wait a week, a month, a year before you have to recall the thing again.
And that way you essentially have something like note cards that you can have tens of thousands of and can only spend 30 minutes a day and actually be refreshing all of that information, all of that knowledge. It's really great. And then for memory palace is a technique that allows you to remember things like the IKEA catalog by placing them visually in a place that you're really familiar with.
Like I'm really familiar with this place, so I can put numbers or facts or whatever you want to remember. You can walk along that little palace and it reminds you. It's cool, like there's stuff like that that I think athletes, memory athletes could use, but I think also regular people can use. One of the things I have to solve for myself is how to remember names. I'm horrible at it.
I think it's because when people introduce themselves, I have the social anxiety of the interaction where I'm like, I know I should be remembering that, but I'm freaking out internally about social interaction in general. And so therefore I forget immediately. So I'm looking for good tricks for that.
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.
that.
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
But the first thing I think of is Lex Luthor. That's great.
Yeah, so I think of Lex Luthor. Because doesn't Lex Luthor wear a suit, I think?
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.
And then I just imagine you talked about stabbing or whatever earlier. Yeah, exactly. Right. Kind of connected and that's it.
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,
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.
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.
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?
We should maybe linger on this memory palace thing just to make obvious because when people were describing to me a while ago, what this is seems insane. I just, you literally think of a place like a childhood home or a home that you're really visually
familiar with and you literally place in that three-dimensional space facts or people or whatever you want to remember and you just walk in your mind along that place visually and you can remember remind yourself of the different things. One of the limitations is there is a sequence to it. So it's, I think your brain somehow, you need, you can't just like go upstairs right away or something.
You have to like walk along the room. So it's really great for remembering sequences, but it's also not great for remembering like individual facts out of context. So the full context of the tour, I think is important. But it's fascinating how the mind is able to do that when you ground these pieces of knowledge into something that you remember well already, especially visually. Fascinating.
And you can just do that for any kind of sequence. I'm sure she used something like this for IKEA catalog, something of this nature.
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?
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?
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...
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.
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.
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.
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.
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
So you mentioned spaced repetition. Do you like this process? Maybe can you explain it?
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.
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.
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.
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?
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.
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,
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.
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.
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?
That's so fascinating. So with space repetition, one of its powers is that you lose attachment to a particular context. But then it loses the intensity of the flavor of the memory. That's interesting. That's so interesting.
Yeah, but at the same time, it becomes stronger in the sense that the content becomes stronger.
Yeah, so it's used for learning languages, for learning facts, for that generic semantic information type of 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...
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.
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?
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.
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.
So it's like you should always be stress testing the memory system.
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.
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?
You know, there's an interesting moment. You probably have experienced this. I remember a good friend of mine, Joe Rogan, I was on his podcast, and... We were randomly talking about soccer, football. Somebody I grew up watching, Diego Armando Maradona, one of the greatest soccer players of all time. And we were talking about him and his career and so on. And Joe asked me if he's still around.
And I said, yeah. I don't know why I thought yeah, because that was a perfect example of memories. He passed away, I tweeted about it, how heartbroken I was, all this kind of stuff, like a year before. I know this, but in my mind, I went back to the thing I've done many times in my head, visualizing some of the epic runs he had on goal and so on. So for me, he's alive.
And part of also the conversation when you're talking to Joey, there's stress and the focus is allocated, the attention is allocated in a particular way. But when I walked away, I was like, in which world was Diego Maradona still alive? Because I was sure in my head that he was still alive. It's a moment that sticks with me. I've had a few like that in my life where it just kind of...
like obvious things just disappear from mind. And it's cool. Like it shows actually the power of the mind in a positive sense to erase memories you want erased maybe. But I don't know. I don't know if there's a good explanation for that.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
I mean, or at least that's one kind of creation.
So imagination is fundamentally... coupled with memory in both directions?
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?
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?
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.
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?
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.
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.
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.
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.
Well, there's a good percentage of time I personally live in the imagined world. I do thought experiments a lot. I take the absurdity of human life as it stands and play it forward in all kinds of different directions. Sometimes it's rigorous thought experiments, sometimes it's fun ones. I imagine that that has an effect on how I remember things.
And I suppose I have to be a little bit careful to make sure stuff happened versus stuff that I just imagined happened. And this also, I mean, some of my best friends are characters inside books that never even existed. There's some... degree to which they actually exist in my mind. Like these characters exist, authors exist, Dostoevsky exists, but also Brothers Karamazov. I love that book. Yeah.
It's one of the few books I've read.
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.
But they exist. They exist, and I have almost kind of like conversations with them. It's interesting. It's... It's interesting to allow your brain to kind of play with ideas of the past, of the imagined, and see it all as one.
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.
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.
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?
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?
Well, that's why a lot of this stuff is both feature and bug. It's a double-edged sword.
Yeah, I mean, it might be why there's such an interesting relationship between genius and psychosis.
Yeah, maybe they're just two sides of the same coin. Humans are fascinating, aren't they?
I think so. Sometimes scary, but mostly fascinating.
Can we just talk about memory sport a little longer? There's something called the USA Memory Championship. What are these athletes like? What does it mean to be elite level at this? Have you interacted with any of them or reading about them? What have you learned about these folks?
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?
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.
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.
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.