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Charan Ranganath

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2024-05-25

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2024-05-25

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1. “And I can get a computational model in 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”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

2. “Record from large populations of cells and then be able to relate that. One, I think the coolest thing gets back to this QR code thing because 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. You're in the metaverse, whatever, right? But it's kind of a crappy metaverse because there's always so much metaverse thing you can do in an MRI scale. You're doing this crappy metaversing. So now I can take a rat, record from his hippocampus and prefrontal cortex and all these areas with these really new electrodes. I get massive amounts of data and have it move around on a track ball in virtual reality in the same metaverse that I did and record that rats activity. I can get a person with epilepsy who we have electrodes in the brain anyway to try to figure out where”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

3. “Basically, as people get older, the activity in the hippocampus at these event boundaries tends to go down. 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. Just watch it. You come out, I give you a test of memory for stories. 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 memory. It's just these little snippets of neural activity. So I think that's a big one. 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”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

4. “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. That's what I was looking for. 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. And so these event boundaries turns out 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”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

5. “I could go this idea of like breaking up our continuous experience into these discrete events, I think was a major discovery.”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

6. “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 are organized knowledge about the world, increase our ability to remember information, just massively increase it. 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. 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.”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

7. “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 writing the book, I was like, oh my God, this is really interesting. How did we do all this stuff?”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

8. “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 kind of gaping holes because you can't keep the magnetic field stable in those spots. You'll see parts where it's like there's a vein and so it just produces big increases 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 MRI scanner, I'm lying down. I'm not interacting with you in the same way that I would in the real world. 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.”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

9. “Not seeing anything there that's particularly interesting. There's still this increase in activity. So it's more sensitive with FMRI. So is that a feature or is it a bug? 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. It's in because if you're thinking about like a story, let's say you're listening to a podcast or something, you're listening to Lex Friedman podcast, right? You're putting this stuff together and building this internal model over several seconds, which is basically we filter that out when we look at electrical activity in the brain because we're interested in this millisecond scale. It's almost massive amounts of information, right?”

   2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

10. “Around that point in space. Okay, so if then something happened, like a sudden light flashed in that part of, you know, right in front of your cowboy hat. I would have a bigger response to it. 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...”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

11. “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, or I'm thinking about the right, even if I'm not looking at it. What you'd see is that there would be this little elevation in activity in areas in the visual cortex, which process vision.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

12. “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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

13. “Getting active after you release it in the gap between the two neurons called synapse. So what's interesting is if you leave that, imagine you're just flooded with this liquid in there, right? 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. 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 what anaerobic metabolism. So they're not using oxygen as fast.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

14. “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, all this stuff. 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 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 kind of being a middleman, so to speak, with the neurons. 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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

15. “Yeah, I mean, it's very slow to the brain 50 milliseconds like it's an eternity. Maybe not 50. Oh, you know, maybe like, you know, let's say half a second, 500 milliseconds, just so much back and forth stuff happens in the brain in that time, right? In fMRI, you can measure these magnetic field responses about six seconds after that burst of activity would take place. 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 this 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 in the neurons like going up or down. But sometimes what you can have is the”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

16. “It was fascinating. So now you have those building blocks for assembling a model of what's happening in the present, 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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

17. “Two different cafes and two different supermarkets. 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, 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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

18. “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 by recording local potentials in the brain, you know, so little waves of activity in, let's say, a human who has epilepsy and they stick electrodes and their brain try to find the seizures. 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? And so we've found that some networks of the brain sort information in memory according to who was there. So I might have like, we've actually shown in one of my favorite studies of all time that was done by a former postdoc, Zach Rea. And 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”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

19. “So to speak, let me try a different analogy to that might be more accessible for people, which would be like you've got a folder on your computer, right? I open it up. There's a bunch of files there. I can sort those files by, you know, alphabetical order. And now things that both start with letter A are lumped together and things that start with Z versus A are far apart, right? 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 closed and things that are far apart in time or far. So every, like you can think of how a brain area or a network of areas contributes to memory by looking at what the sorting scheme is.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

20. “Memories that occurred in the same place have a similar QR code and to memories that occurred in different places have different QR code. 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. 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. And the hippocampus is just putting it all together into these unique things that just are about when and where it happened.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

21. “That's bright in the hippocampus and one that's dark. And if I'm remembering something like more like the car that I used to drive when I was 16, I might see the opposite pattern where a different pixel spray. 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 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, this would be Stone Age, but a flying machine learning techniques to do decoding and so forth. And now there's a lot of forward encoding models. You can go to town with this stuff, right? And I'm much more old school designing experiments where you basically say, okay, here's a whole web of memories that overlap in some way, shape, or form.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

22. “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. 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. And that allows us to see, hey, there's an increase in activity in some part of the brain when I'm doing some task 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 from, because maybe when I'm remembering this thing, like I'm remembering the house where I grew up, I might have one pixel.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

23. “That does because you have hemoglobin that carries the oxygen, the iron basically, in the blood that makes it red. 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. So I gave you, I think I sent you a GIF, as you like to say.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

24. “So three 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 radio frequency pulse, which is basically a different electromagnetic field. 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. So they're all, we tweak them in different ways. But the basic idea that we use in ephMRI 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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

25. “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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

26. “The connections between different events, yeah, 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. Find the signal and the noise.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

27. “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. 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 sleep and its real role in helping you see the connections between different events that you've experienced.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

28. “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? 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 in the world. So it almost is like a little people call it replay. 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”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

29. “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. 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 basically 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 most highest information content and value.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

30. “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. 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 like we need to do some work on it for further analysis, 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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

31. “There's a lot of variability, I think, that, 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 like basically what they call like 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. Like I know how to get from here to, let's say if I walk here from my hotel, I could just rigidly follow that route back, right?”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

32. “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 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 are a mental maps of the world just like our memories for events are not photographic. I think there's this combination of actual verifiable details and then a lot of inference that you make.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

33. “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 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, 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? 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 like, what if?”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

34. “And so it goes into a much more predictive mode. And you have these event boundaries, for instance, and you have, 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 so the new direction we're going in is understanding navigation in our memory first places. And the reason 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'll 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 I think that probably may happen when you have like absolutely”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

35. “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 it, when you study.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

36. “Things, not like things that would be. You'd be able to bring a lot of prior knowledge, but they build the skills that you need to memorize arbitrary things.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

37. “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 getting chemo for cancer. And so he decided because 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 you know orders of cards and so forth so there tend to be pretty arbitrary”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

38. “There's a guy named Henry Rogersher who's studying these guys, and there's actually a book by Joshua Ford called Moonwalking with Einstein, where he talks about, he actually, as part of this book, just decided to become a memory athlete.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

39. “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?”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

40. “Yeah, there was actually this famous mnemonist who's kind of like back then the equivalent of a memory athlete, except he would go to shows and do this, those described by this really famous neuropsychologist from Russia named Luria. And so this guy was named Solomon Sheroshevsky. And he had this condition called synesthesia that basically created these weird associations between different senses that normally wouldn't go together. 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 the drinking was part of this.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

41. “I love that book. 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 Caramanta. But they exist.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

42. “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 when our common ground that we're establishing in language requires using those building blocks to put together a model of what's going on.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

43. “What they found was there's Daydreaming network. And I thought this is just ridiculous research. Who cares? But then what people found was when people recall episodic memories, this network gets active. And 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, 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 in various subpieces, is that basically it's kind of taking apart.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

44. “I think so. I mean, it's not clear that it isn't 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 are find it very difficult to give you a scenario 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. As partly because when you have amnesia, you're stuck in the present. 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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

45. “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 taper 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 out one thing, you're just ruthlessly recombining things without any necessary kind of goal in mind. Or at least that's one kind of creation.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

46. “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's 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 Hasibus did work on this with Eleanor Maguire in UCL. And this goes back actually to this guy Frederick Bartlett, who is 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. You give people stories and poems, ask people to recall them. And what he found was people's memory.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

47. “How do we tell? I get some mental experience. Where did that mental experience come from? And it turns out this is a huge problem 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 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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

48. “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 is like 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, but one of my former mentors, Marcia 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”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

49. “Yeah, and feel good about it. You know, 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 learn. This is how I learn 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 acted out and you're going to botch those lines from time to time, right?”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source

50. “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 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.”

    2024-05-25 · Lex Fridman Podcast · #430 – Charan Ranganath: Human Memory, Imagination, Deja Vu, and False Memories · IDENTIFIED FROM THE TRANSCRIPT · source