Why We Remember with Neuroscientist Charan Ranganath

Episode Transcript

Dr. Correa:
From the American Academy of Neurology, I'm Dr. Daniel Correa.

Dr. Peters:
And I am Dr. Katy Peters, and this is the Brain & Life Podcast.

Dr. Correa:
We're back here with the Brain & Life Podcast. Katy, how are you today?

Dr. Peters:
I am doing well. Getting ready to move to my new house. The stress is coming. How about you?

Dr. Correa:
Yeah. I'm glad not to be juggling multiple spaces. It's easy for us in one-bedroom apartment in New York. What's funny is we on our day hours are physicians at work, but somehow that doesn't always end up limiting to just the work day. How many of your friends and family ask you about memory, how it works and how to improve their memory?

Dr. Peters:
I would say a fair amount. I would say that definitely my family will ask those questions. I do hear it more from my patients and care partners because my patients with brain tumors, memory difficulties can be common after surgery or radiation therapy. But what I think that's really important, whether it's you're educating family and friends or your patients and their care partners, is that sometimes a memory issue is not really a pure memory issue, it can be an issue of attention. And so asking questions and probing where are those memory problems can be very appropriate. I do like to send people to occupational therapy or recommend occupational therapy or recommend neuropsychology to evaluate it appropriately because I think you really want to demonstrate where the challenges lie and then have someone to help design strategies and techniques to improve their memory.
For me, I know one of the things I do is I try to make lists. Often a grocery list so I can remember what to bring. But my challenge is after I write it down, I can barely read my own handwriting. So I'm often looking at the list and this is supposed to prompt my memory, but I can't read those scribbles. So I need to work not just on memory, but my handwriting skills. How about you?

Dr. Correa:
Yeah. No. I think the first place I notice and I also will bring up for people is like you said, sometimes a challenge is an issue with attention. And yeah, we often will think of attention much more as just like whether or not someone is paying attention. But there are so many other things that affect our attention. Chief among them is our sleep and our rest. And so many people who are having challenges with their memory will often when you admit or say they have not been sleeping well. And after you have some days of sleep deprivation or having a sleep deficit, it really impacts your ability to pay attention. Even if you think you are really trying to focus your brain's ability to maintain focus and attention is really impacted. And we've seen that in medical students and doctors that are studied after nights working and in many other individuals in various studies. And so that's often a first place. And when I feel like I'm having a challenge with focus and attention, the first thing I'm stepping back is thinking, okay, how have I been sleeping and how can I improve that?
And so we wanted to continue some of that discussion that we've had before. We had an episode learning about unique types of memories like highly superior autobiographical memory. And in that episode we interviewed Dr. Craig Stark as our scientific expert. And then we'd had a follow-up episode with Dr. Craig Stark to delve in a little bit deeper into how memory works. Today we're continuing that discussion with another neuroscientist from California. Dr. Charan Ranganath. After reading his book, Why We Remember it struck me that he brings up many of the topics we end up discussing about memory with our friends and our patients. And I really feel that through this discussion and taking a look at the book by growing our understanding of how memory works, it can help us reinforce how we learn or how our memory functions and have deeper empathy when others are having challenges with their memory or memory disorders.
And please make sure to check out in the show notes the links to the information for Dr. Ranganath's book, but also for in our show notes for the link to our survey. We're working on getting a good representation and feedback from you guys in a listener survey. The link is brainandlife.org/survey. And by participating you can help us learn what topics and areas that we should be going and ways that we can change the show to improve the information we bring to you and really help us understand who's listening and how we can reach more people. If you participate, you get a chance to enter a drawing for one of five $100 Amazon gift cards.
Welcome back to the Brain & Life podcast. I am so glad that you're here again with us and we're going to continue some of our brain wonders topics. So this week, instead of interviewing a community member or an individual or a caregiver living with neurologic conditions, we're going to learn a little bit more about how our brains and memory works. And today I'm joined by Dr. Charan Ranganath. He's a professor of psychology and neuroscience at the University of California at Davis where he directs memory and plasticity lab and the dynamic memory lab. For over 25 years he has studied how our brains remember and what has happened in our lives using brain imaging, computer models and working with individuals who are living with memory disorders. And recently in his book Why We Remember he explores the intricacy of our human memory. Thank you so much Charan for joining us today.

Charan Ranganath:
Oh, it's very exciting to be here. Thank you, Daniel.

Dr. Correa:
So I wanted to learn a little bit more about you. I see guitars in the background, not always with a thought when they say and talk about a neuroscientist. So outside the lab, the therapy visits, research papers, who is Charan?

Charan Ranganath:
That is the million-dollar question. Well, so the guitars are because I've been playing music I guess since I was in junior high, but playing guitars since I was in high school. I'm still not much better at it than was when I started. But music is ... I guess if you had to ask what's the closest thing to who I am, it would be music I play. I've played in a few different bands. I'm playing in one now. I also play in a band that gets together at neuroscience conferences called Pavlov's Dogz, and that's a cover band where we get together twice a year and play at various ... Play actually clubs, but they're associated with conferences that would bring us together anyway. So just a quick plug, by the way, we're playing in Chicago at the Society for Neuroscience Conference at a club called Reggie's.

Dr. Correa:
All right. So if we want to listen to good music and then also learn about our brain, maybe check out the Pavlov's Dogz in Chicago.

Charan Ranganath:
Exactly. Exactly. Yeah.

Dr. Correa:
So let's talk about it and build on that. You talk about your own experience with music. Has music itself been a factor that draws your interest into how memory works?

Charan Ranganath:
Yes and no. I would say that I try to keep my music very separate from my other activities in the sense that you can't help but get with work something that you're doing for a living, you can't help but get sucked into the ambition part of it as much as I try not to. And I don't want that to affect my music at all. So I know people who will write songs about their science and stuff and that's not me. But at the same time, I'm a person who remembers. And I think like many of us music is just this vehicle for autobiographical memories. The memories of our real personal experiences. And so I go through periods of time where I listen to some song and that song later on becomes a little tag for an experience that I've and can bring back all these other memories of that time period.

Dr. Correa:
And we've had a previous episode with Marilu Henner who has highly superior autobiographical memory. And in that episode and on a follow-up, we did a discussion with Dr. Craig Stark about that phenomenon. But I'm interested on the other side of it. We've seen musicians who play huge scopes of many different songs and many different albums and they'll get up on stage and play a song from years before. I'm wondering just even that in that idea of thinking of a song or remembering how to play chords for a song that you haven't played in years, how that itself becomes a way of exploring what we understand about memory.

Charan Ranganath:
Well, one of the interesting things about that kind of expression of memory is that to really do it well, you're doing it without any awareness of how you're doing it. People often call it memory without awareness, but that's not quite right because it's like if I'm playing guitar or somebody's playing piano or somebody's dancing, it's not like they're not aware that they're doing it. It's just that you're not going back and consciously remembering when and how you learned that event, that skill that you have. So in other words, if you went and got on your bicycle and if you know how to ride a bike, you wouldn't ask yourself, okay, what was I doing the last time I rode a bike. Pushing down the pedals and so forth. You just do it.
And part of skill learning is developing that automaticity and that independence. The first time you get on a bike or you try snowboarding and so forth, it can be a very conscious experience of, okay, I just fell down, what did I do there? And part of that learning curve and moving up the learning curve is that ability to transition to automaticity. And at that point it becomes a very robust memory. So you can look at people who even have quite advanced Alzheimer's disease and if they used to play music before, they can just come alive when they play music again or people who are dancers can dance even when they're quite memory impaired. So it's this remarkable ability we have to basically build these new memories that initially are memories of experiences we've had, but then they can become hammered in through trial and error. And we can talk more about error in learning. To this motor program that can basically function best when we're not remembering per se, we're just doing.

Dr. Correa:
So one of the key ideas or themes that I see in the book as you described and talk about the idea of remembering self versus the experiencing self and how that fits in with decision making. How do you explain this to a community member that you're speaking to?

Charan Ranganath:
I can't take credit for the distinction between the remembering self and the experiencing self. That actually came from Daniel Kahneman who was a professor who I took a class from when I was an undergraduate. And that's another interesting case of memories shaping your decisions themselves. Because Kahneman was really interested in decision-making but his research over and over again was really about how memories affect our decision-making in ways that can sometimes make them irrational. And his major point when he talked about the distinction between the remembering self and the experiencing self is we experience so much in our lives and yet our decisions are only based on that subset of material that we remember in the moment. And as a memory researcher, I've always thought that's a profound concept because every memory researcher knows that the majority of the details of our experiences anyway will be forgotten.
And even the ones that you have memories for, you won't always be able to access them when you need it. And so putting those two pieces of information together, it really gives you a sense of how all we carry with us is our memories. There's nothing else. And that can have all sorts of impacts. For instance, for me, I just went on a vacation that was attached to a conference that I went to in Germany. And so I met up with my daughter and my wife and we did a road trip through Austria and Slovenia, which is where my wife's family originates from. And it was in memory a great holiday. But during the experience I struggled with insomnia. I was having to go through airport security and dealing with flight delays and had a mishap with my car rental. And these are all things in some sense I remember them. But I went through that decision process knowing that this would be the case. Knowing that there are all sorts of hassles with taking a vacation.
Because when I look back at New Year's Eve and say, what did I do in the past year, I won't be remembering the times I sat comfortably watching TV. I won't be remembering the times that I was clicking through my Facebook feed. I'll be remembering this vacation that I took with my wife and my daughter and her partner. And that was really the motivating factor for these decisions is investing in memories because all we have in 90% of our experiences is the remembering self.

Dr. Correa:
And in that instance, you give a situation where we're effectively in a way pruning out certain aspects and making decisions about not just what to do, but what we remember and how our perspective and interpretation on it is. And our brains are constantly bombarded with information from all kinds of different angles. And what we remember, if we remember anything can be influenced by so many possibilities. What are some of the factors that influence what we remember and what we forget?

Charan Ranganath:
That's a great question with many, many answers, but I'll give you just a couple or a few maybe. So one factor is just purely importance. And what I mean by importance is not necessarily what we're intellectually thinking of as important as much as part of how our brains are deciding what is important. And obviously we are our brains. But our brains were shaped through evolution to prioritize certain kinds of experiences. And these experiences are typically things that are associated with emotional state. So for instance, fear, anxiety, desire, lust, love, and all of these emotional experiences are associated with these basic motivational systems that are associated with the release of neuromodulators. Chemicals like norepinephrine or dopamine, serotonin. And these are the basis for many psychiatric drugs and drugs and neurology and so forth. But we know that they promote plasticity and they focus your attention in particular ways.
And so when you have these moments that are very important in a biological sense, things like I just saw a bear is chasing me, or things like I almost got into a car accident, or Hey, this person who I was attracted to looked at me, these kinds of experiences are going to be the ones that people tend to remember. Now another factor is when we're motivated to remember something and we focus our attention on those things that we're trying to remember. So you tell me your name and I'm focusing my attention and I'm trying my best to remember your name. But if I'm checking text messages while you tell me your name, I've already lost the battle. I'm not going to get much in. I'm going to have a very impoverished memory. So that's step two.
Step three is overcoming interference. And what I mean by that is we tend to think of memories being like if I look for something, I should just be able to push play on it. But in fact, it's more like trying to find something on a very cluttered desk. So I can look at my desk right now as an example. And suppose I put a post-it note somewhere on this desk and let's say it was the same color as other materials on the desk, I would have a lot of trouble finding it. And likewise, if I'm trying to remember something and I have a memory for it in there somewhere, but it's very similar to all of these other memories that I've experienced. Things like names for instance.
So your name is Daniel. Well, the drummer in my band when I was in grad school was also named Daniel. The bassist in my previous band was named Daniel. So just there, I've got two Daniels that are competing in memory for the memory of your name with your face. And that's why people all the time, the most common thing that people report to me is that I can't remember the names associated with faces. And the reason is that it's not a matter of simply remembering someone's name, but remembering which name went with which face. Many people have heard the name Daniel, many people have probably even heard the name Correa. But being able to put those together with your face is utterly arbitrary in the sense of there's no meaning that you can use to attach that.
So that's a big challenge that we have is forming a memory that can stick out somehow from the clutter. Because if we can do that, if I could form some kind of a memory for this experience that's very unique and stands out in some way that distinctiveness can really help me find that memory again later. And then the final piece of it is having the right cues that you can use. So in the case of your face, if there was something that I could use to say, "Hey, there's some cue in the space that reminds me of your first name or your last name." Or even if I can bring back something about this conversation that might help me pull up the information that is associated with your name. That would be great because then I have a cue that the next time I see you can just pop up into my head. And I'm not very imaginative with these things. I'm sure you could talk to memory experts who are great at this stuff, but that's why I'm terrible with names. But that's part of the trick.
And you can think of this other ways too. A big example I like to give is if it's garbage day and I'm coming home, I ride my bike home from work, if I know it's garbage day and I have to take it out tonight, what I'll do is I might imagine myself putting the key in the front door, and then imagine myself all of a sudden glancing at something near the door like a plant or whatever, and saying, "Oh wait, I've got to take out the trash," and then imagine myself walking over to the trash taking the can out. And so what that does is when I see the door, I see the plant, they're going to serve as cues that pull up that memory quite naturally.
And so I actually talk about this technique as planting cues. I should have put it in the book, but I came up with that afterwards. But the idea there is to be able to have some kind of a reminder that's outside in the world so I don't have to search for it. But if you don't have the right cues, if you have a blurry memory that doesn't stick out from everything else, if you never paid attention, if it wasn't that significant in some way, those are the memories that you're going to lose, which is a lot of our experience to be honest.

Dr. Correa:
And one thing we do know is that even maximizing attention and reducing interference, our memories are not necessarily these perfect pictures or videos of a context. And then the next time we think of and remember that great dinner or that childhood experience, there's an opportunity for that memory to actually be altered or impacted by our current experience. Can you tell us a little bit more about that and how you explore it in the book?

Charan Ranganath:
Yes. One of the things that I think is so counterintuitive to people is the idea that we don't replay the past. It could sometimes feel like if you have a vivid experience of remembering, it can feel like I'm actually replaying a movie in my head. But that's not really how it happens. There's lots of research to show that people really extract meaning from their experiences and they associate things that happen with their beliefs and their knowledge about the world. And so we use that as this foundation and we will remember some little bits and pieces of an event. But basically what happens is we use those little fragments of our experience and we use our knowledge about the way things work in the world, and then we imagine how the past could have been. And that is what remembering is in the real world. It's really imagining the past.
Now when we imagine things, we can imagine things that did happen, and we can imagine things that could have happened but didn't happen. So right there, there's an element where our memories can become a little bit distorted. Now, every time I recall this event, again, I'm not replaying it, I'm actually opening up the memory to be updated. And there's many different explanations in psychology and neuroscience for how this can work. But the end result is the act of remembering can change the memory. It can actually strengthen it in some ways, but it can also lead to it being weakened or it can lead to it being distorted. It can lead to other memories being weakened or distorted in fact.
And so in the book, one of the analogies I give is how when I was playing in a band, I used to actually photocopy flyers for my band. For those people who are old enough to remember photocopiers. Back then you'd copy something and the copy would be distorted. And if you made a copy of that copy, the copy would become more distorted. And so what happens is over time, if you make a copy and then you make a copy of the copy and then a copy of a copy of a copy, eventually the significant parts that are common across these copies will pop out more and more and everything else just gets distorted to the point where it becomes almost unrecognizable. And so that's in effect how our memories work. If I remember something over and over and over again, the significant stuff that's common across these experiences of remembering will pop out and a lot of the other stuff will drop out. And the reason is that essentially every time we remember that memory of the original event also has the residue and the effects of every time we've remembered it in the past.

Dr. Correa:
Yeah. The way I've explained to people before is that we're only ever remembering the last time we remembered it. Yeah.

Charan Ranganath:
I think that's true. Just to be fair, we can remember things that happened that we failed to remember the last time you remembered it, but absolutely the last time you remember it can influence the way you remember it now for sure. And we tend to think of this as bad. We tend to go, oh, our memory should be 100% solid as a rock. But the thing is that in fact, our memories actually benefit from changeability because what happens is, for instance, the act of recalling something over and over can make the memory stronger and it can make the most useful parts of the memory stronger, which is super important. So that the fifth time I see you, I can pull up your name very easily because I've pulled up the name in the past many times. And so we want to be able to do that, and I want to be able to remember your face in a way that's not tied to any particular place and time and context. And so these are things that we've modeled using computer models, and we just have a paper that came out recently that talks about how this malleability of memory can actually help us form memories that really last. And we can get into that more if you want. We can talk about spacing effects and error-driven learning and so forth.

Dr. Correa:
So I was thinking next, I wanted to talk about really this practice of memorizing, of working on your memory. In the book you share story of Scott Hagwood and how after being diagnosed with thyroid cancer and looking towards what was going to be many rounds of radiation therapy he was aware of and was told of how his memory could be impacted by his treatment. He was so concerned about that and his treasured memories and his connection to those around him that he looked at ways that he could practice his memory to sustain that to an extent where he became quite well known for his memory. But tell us a little bit more about his practice and what that turned into.

Charan Ranganath:
Yeah. So Hagwood really was worried about this phenomenon called chemo brain that I think a lot of your listeners probably know about. And it's this phenomenon where people going through chemotherapy will report brain fog and all these cognitive deficits. And I hear about this quite a bit. It's actually a fascinating topic when you get into so many conditions that have these kinds of brain fog associated with them. But he was concerned about his memory. And so he picked up this book to develop tips to improve his memory. And he got so into it that he was able to use these tricks to memorize vast amounts of information. And eventually he went into these competitions. And so there are these memory competitions where people who are called memory athletes actually compete against each other. And they'll do things like ... I am making this up in some ways, but it's like memorize pi as many digits as you can, or more likely they'll go, here's a deck of cards, I want you to memorize the order of each card in this deck. You have 30 seconds or whatever. And so they give people all of these different challenges. And Hagwood became the world memory champion just by virtue of working on these techniques over and over again. It's quite a remarkable story.
And one of the things that he said is he's not remarkable as a person. And you could argue whether ... He's quite remarkable in certain ways. But I think it's fair to say all memory athletes will tell you that they didn't have a remarkable memory ability coming in. It's really learning skills and tricks and ways to rapidly process and manage the information that they're trying to memorize. And what it comes down to is if I'm trying to memorize as much as possible, don't strive to memorize more, strive to memorize less. That is leverage as much knowledge as you can and latch on everything that you're trying to memorize to the stuff that you already know. So for instance, people like Hagwood would take, let's say a card and they would make a little code for each card, and then what they would do is they would make up a story that would give them the order of each card in the deck. And so once you learn these skills and make them automatic enough, just like the piano player we talked about, you can basically take this information, attach it to information you already know and spin it out very, very quickly.
And all memory athletes use these skills that are basically linked to particular kinds of things that you can memorize. And this goes back all the way to the ancient Greeks would use a method called the method of loci. People who watch the TV show, Sherlock would call it the Memory Palace. Where if you're trying to memorize things, a good way to do it is to imagine them in different rooms in a house. And attaching that information to a structure that you already know helps you preserve that information that you're trying to memorize and keep it protected from interference. It's mind boggling, but it's true.
If I think of a bunch of Spanish words that I'm trying to memorize and I put one in a mental room in a house and I put another in a different room in that house, it's protecting those words from interference. It's really a pretty remarkable thing. And people going back to, if you look at the Ramayana or the Iliad, all these epic poems, people would memorize them and then they would deliver them. They would use songs as a vehicle to memorize too. And so all of these advanced feats of memorization come down to taking something that is arbitrary and meaningless and sometimes trivial and latching it on to a structure of knowledge that you already have.

Dr. Correa:
And in that practice, how can we ... We've talked about a few things, increasing attention and reducing interference and a few examples of that. But how can we take some of those practices of memorizing a deck of cards or the ideas of loci and the memory palace in some more of our day to day if we want to really have that time where we want to remember a great experience that we're having with our niece?

Charan Ranganath:
Well, one thing I'll say is that I can tell people gobs of memory strategies. And to be honest, I don't even know that many of them, but you can read a book and go to a website and find many, many, many memory strategies that can help you remember names, they can help you remember faces, they can help you remember directions to a place that you've been to whatever. And there's different skills that you could use for different kinds of things. But the biggest problem that I see is that people don't use the strategies. So I can teach you as many things as you want, but if you don't use them, then you've lost the battle. So why don't we use them? A part of it is I think we just expect we should get the memories for free. And so you don't actually ask yourself from the beginning, what do I want to remember in the first place? What is important? We might think about it in retrospect when we can't find that memory. We go, oh, I wish I remembered this. But in the moment, you don't go into these events with intention of what do I want to take away? So that is the first step is going into our experiences with some kind of intention.

Dr. Correa:
So memories take the same level of intention as relationships?

Charan Ranganath:
Exactly. Yeah. Yeah. And often those two are directly related to each other. You want to have a good relationship, you invest in the right memories. So for instance, a lot of people when they have an experience in their life, like what you talked about, let's say somebody's trying to remember their child's quinceaÃ±era or they're trying to remember the wedding of their sister or something like that, the birth of their child, sometimes what happens ... Maybe not during childbirth. But sometimes what happens is people try to document it and mindlessly just take videos and pictures. And people generally have the assumption that if they're taking a video or a photo that they will remember it. And what often happens is that in fact, photography and videos actually reduce people's memories for events. And the reason is that if we over document, we don't go back to those photographs and videos very often. And then the other part of it is it actually takes us away from the experience.
So if I'm sitting at a concert and I've got my phone up and I'm holding it up, I'm recording, my mind is where my phone is, and I'm capturing this recording of this person who's singing. But the memory I want is not the memory of what this person is singing because I have the record for that. I can play it on my streaming service if I want to. What I want is the memory of the experience of being with my friends, of that emotion that's coming up, of that feeling of connection with the artist. And so if I'm not using the camera in a way that accentuates those factors, I'm actually depriving myself of the memory that I will want later on.
So what you can do is you can use documentation in a way that actually brings back those things. Maybe take a couple of pictures or take a short video of when the artist is really doing something that is just moved you in some way, but focus on that feeling when you're doing it. Take pictures of your friends and how you're joking around and laughing or really getting into it. And don't do it very often. Do it very sporadically, selectively and get the thing that will be very likely to pull you back into the moment later on. And then go back to those things and use them as cues to recall the things that you wanted to recall from that event later. And that's really a great recipe to remember the stuff in life that's important.

Dr. Correa:
Artists themselves are sometimes amazingly present and absorbing the things and experiences around them. It may then end up informing their art, and many of the time they probably also do it listening to other music. In your book you tell the story and then highlight how many different artists, including George Harrison, David Bowie, many different modern artists have been accused of copyright infringement or plagiarism, but it's a little more complicated, the whole idea of how our memory interprets our previous experiences with music and language, and then that gets expressed in art. Can you tell us a little bit more about this concept that you put together in the book called cryptomnesia?

Charan Ranganath:
Yes. Yeah. And just as a background for this, I think it's important for people to understand that creative products come from memory. And there's this beautiful link that I just mentioned previously about this link between imagination and memory, but it goes in the reverse direction too. That when we're trying to create things, we often draw upon memories to do that. Now sometimes that creation can be something that's very novel and unique and the whole is different than the sum of its parts. But sometimes what happens is if we're not aware of what we're doing, we can unconsciously just regurgitate the influences that we've had. So a good example of this was George Harrison who wrote this song, My Sweet Lord. And so he wrote the song called My Sweet Lord, and later on was sued because it bore a strong resemblance to He's so fine by the Chiffons. And so the judge said, "I don't think that you did this on purpose, but it's clearly infringement." And he got really mad about it and said, "Oh, well all rock and roll is like this." So I think you get all kinds of excuses.
But what happens is if you listen to something over and over and over again, what happens is it's sort of like a tire that goes through the dirt, and if you go through again and again and again, it builds up this little rut in it. And so after a while, the car will naturally settle into the rut, and that's how it will move, because that's the easiest way to get the car to move if that makes any sense. And so likewise, we can do this with memory. That is just saying a word over and over and over again can make it more fluent and make it easier to spit out. And the same is true for listening to a song. If you listen to a song over and over again, it can make it more likely that when you play a few notes that you're going to unconsciously just settle in to that entire riff that you were listening to over and over and over again.
And the reason is their brains are trying to optimize towards making things predictable, making things automatic, making things easy. And that's a kind of learning that happens even if we're not trying. Our brains are always optimizing and shaping and so forth. And so that's why cryptomnesia happens. It's not necessarily because somebody's consciously trying to copy something. I would argue that more often than not, people just naturally do it because they are just unconsciously expressing what feels natural to them. And what feels natural to them sometimes is relying on things that they've heard many, many, many times before.

Dr. Correa:
So what do we understand about our memories and this functional process that can help us get out of the rut?

Charan Ranganath:
I think one big part of how to get out of ruts in general at least in terms of creativity, is to make sure to draw upon many different kinds of sources. So if you are trying to make music, don't just listen to one genre of music. Don't just listen to the Beatles over and over again, whatever. Listen to many genres of music. For me, I love African R&B from the 1960s. I think it's just fantastic music. I don't play anything like it, but it's something that inspires me in particular ways. If you look at people like Picasso was really into Japanese masks. The Wu-Tang Clan is one I love to talk about. Who would've thought to combine imagery from martial arts films and science fiction and the nation of Islam all into these hip-hop songs? That's the ultimate kind of creativity.
And so I like to say using the language of machine learning, it's that you want to diversify your training data. And that can be just even in your everyday experiences. I think generative AI programs will never have the kinds of unique experiences that you and I have because we're interacting with people in the real world. And you had some really unusual person who came from a country that you had never even been to before who was your roommate in your dorm in college. And that gives you memories that you can draw upon in new ways when you create things if you were to write something or make a song and so forth.

Dr. Correa:
So increasing the diversity of our experiences then will broaden and strengthen the quality of our memories and our experiences. That's great.

Charan Ranganath:
I think so. Yeah. I think that is a big secret to creativity.

Dr. Correa:
So I think for many artists and for all of us, memories also have a deep connection to our emotions. You describe it in the book, you explain for your readers the structure of the hippocampus and its connection to the amygdala and how there's a role and the loops that sometimes lead to our anxiety. How do you explore more of that and explain that more to your family members and people when you're talking to them about the connection between memory and anxiety?

Charan Ranganath:
Well, some people say and thought I was the only one who said this, and then I've heard this many times after, so I don't know who said it first. Is that depression is associated with thinking backwards and memory working backwards and anxiety is associated with memory working forwards. So the idea is that depression is often associated with rumination and thinking about bad things that have happened to you and bad things that you've done and so forth. And anxiety is about projecting things that could happen into the future. And in both cases, memory is fundamentally at the center of them. And one of the weirdest findings in neuroscience research is that if you look at studies of animals that have damage to the hippocampus, if you damage part of the hippocampus, that in humans would be the front most part, what they find is that in fact, these animals show this loss of anxiety and they're much more likely to freely explore places where they would otherwise be nervous or they would look nervous and look like they're anticipating a threat at some point.
And so some of what I think is going on there is that memories give us some sense of predictability, and that can also tell us when we're failing to predict something, it can also give us the sense of anxiety and uncertainty. And one of those things that you find with people with memory disorders is they're often quite placid and calm. People with a pure amnesia that doesn't affect more emotion related parts of the brain are often very zen about things. They're in the moment. They're not thinking about what could happen. And I think memory is this beautiful tool that can tell you what could happen, but it can also run awry and lead us into all sorts of negative places. And then on top of it, there's the more basic factor, which is that we are biased to remember things that are emotionally intense. And for people who are anxious, those are often going to be negative threat related memories, things that are associated with shame or embarrassment or social rejection or pure fear in some way, shape or form.
And so those are the memories you're going to draw upon when you're anticipating what could happen next, both consciously and unconsciously. And sometimes the emotional learning that takes place via a brain area called the amygdala can express itself very quickly before you've really had a time to consciously remember. And so you get that feeling that something bad has happened or is about to happen. And then what do people do when they have that feeling? Well, they fill in the blanks with memories that could tell them what could happen or it could be happening right now. And so there's this cycle between the brain telling you there's a threat, and then people using memory to fill in the blanks and then magnifying that feeling over and over. And I think that's characteristic of many anxiety disorders.

Dr. Correa:
So in the book on our podcast and lots of different sources, people have heard about the importance of sleep, particularly as a key component to their memory consolidation. But in the book you also explain a little bit more specifically why sleep is so important to not only the process of preserving our memories, but then actually strengthening our memory source. Can you get into that a little bit to share for our listeners to help us remember that it's important to sleep?

Charan Ranganath:
Absolutely. And I should say when I've looked into it, my feeling is, and I'm sure you can get this from sleep researchers, is we are only at the tip of the iceberg in understanding all of the ways in which memory benefits from sleep. There's some very basic things that we know. For instance, recent work suggests that during sleep, the brain is flushing out certain toxins like amyloid that builds up over the course of a day. And so there's a homeostatic element to sleep and a preserving element to sleep that's restorative. But then on top of it, we know that memories are actually replayed in really interesting ways during sleep. And this happens in different stages of sleep. So during REM sleep, even though we feel like we're asleep, the brain waves that you can record actually look like somebody is in many ways, they resemble waking EHE brain waves. And that's when we have many kinds of dreams where we even feel conscious.
And REM sleep has been highly connected with motor learning. So if you're trying to learn a new skill, REM sleep seems to be involved in that. You can also see, just as an aside, and I'm sure many of your listeners can appreciate this, is that if you're trying to learn a new skill, even in those first couple of stages of sleep where you're just drifting off, you'll often feel yourself replaying those physical experiences. So it's like the few times I've gone snowboarding when I go to bed, it's like I'm just feeling myself going down the hill. And that seems to be something that happens during sleep. And then another part of it is during slow-wave sleep, we know that the hippocampus, this brain area that's very important for episodic memory, engages in this beautiful dialogue with the neocortex, these areas that process these experiences during the daytime.
And what you see is these kinds of cycles of activity of the hippocampus reactivating some memories in the cortex and then the cortex sending information back into the hippocampus. And so the standard story people have in neuroscience is this is consolidating memories. It's solidifying the memories that we have. But the data on that is not as strong, I think, as people would like to say. And more importantly, it's based on this very static idea of memory that it's like you have one memory, but memory is actually this ecosystem. There's all of these different memories that we have. And I think one big thing ... And we've modeled this and we've shown this experimentally, is during sleep you can reactivate an experience, but when that experience is activated, now the brain can free associate and link it with other experiences that you've had at different points in time.
And so what happens is that you're not just pulling up a memory and strengthening a memory for that event. You're actually building knowledge by retrieving these memories because you're taking new experiences and incorporating it into the structure of knowledge that you already have. And you're also becoming more fluent at using the information from those experiences. So there's some work suggesting for instance, that if I memorize a bunch of words in a new language after sleep, you're more fluent in being able to use those words in a sentence. It's not just that you've memorized it better. You can actually use that information. And there's some evidence, it's very controversial, but there's some evidence to suggest that even people can somehow get the big picture and be able to more creatively solve problems that they've been struggling with if they get the right kinds of brain activity during sleep. So it's not just important for stabilizing memories, but for really making our experiences useful and actionable. And so that's part two.
Part three is if you don't get sleep, you are in bad shape. And I know because as I'm getting older, I'm having sleep problems. And I think this is one of the challenges of aging, and it definitely affects people's memory as they get older, is your sleep gets screwed up. And of course any new parent knows this intuitively because you're not getting much sleep. But when you're sleep deprived, the hippocampus isn't functioning very well, the prefrontal cortex, which is an area that's super important for regulating what you're going to be paying attention to for searching for information or memory. Prefrontal cortex is shot when you have sleep deprivation, your stress reactivity goes up, which further affects your ability to retrieve memory. It's just so bad in so many ways. So there's positive effects of sleep, but there's also negative effects of not getting sleep. And so if you put the two together, that's where you really start to see how important sleep is.

Dr. Correa:
Yeah. For me, as my ability to just fall asleep wanes and has become more tenuous. I found it's one of the things I like most about when I'm physically active or my exercise and activity is it helps me have better drive and feel greater amount of sleepiness to be able to fall asleep in the night. And Charan, you said that this act of working on the book and pulling all these ideas together, also sharing your own perspectives was one of the hardest things that you've done. I'm wondering, is there something that you learned and changed your perspective of about memory and your studies from the work of writing the book or even as you've been out now meeting and talking to people about the book?

Charan Ranganath:
Yes. Very much so. I've become aware of how many kinds of work are important in the basic science sense, but people overreach in terms of saying how much that generalizes into real life. There's other areas of work that are not necessarily seen as mainstream, but in fact are highly relevant to people's daily life. So for instance, one chapter I wrote was on a concept called collective memory, which is how our memories influence other people and how other people's memories influence us and how collaboratively we work together to remember things. And that has huge implications both for people's everyday memories in terms of child development, in terms of our emotional health, in terms of the rise of misinformation and societal development. But most memory researchers don't think about it because it just thought of as a fringe topic. But now I realize just how embedded our memories are with other people's memories. It's on the one hand obvious, but on the other hand, it's just very profound when you really think about the implications of that.
Another thing that I thought about while writing the book was I came across some stuff that was talking about memory, not from the perspective of ... The standard narrative we have in memory research is children have bad episodic memories. They're bad at remembering the events from their life. Then as people become adults, you have this great episodic memory functioning, but that's only about a five, 10 year period. And then when you hit your 30s, memory decline starts and your episodic memory gets worse and worse. And it's just bizarre. I've always thought about that as a bizarre thing. Why would our brains be designed to be optimal for such a short period of time? And so this other perspective is saying, no, memory is doing what it's supposed to be doing throughout your lifespan. You want to have a memory system that's fairly not tied to a particular context and that's fairly open, and you want to learn through curiosity and exploration when you're young so that you can pick up as much information as possible from unpredictable sources.
Then at some point what happens is you become an adult and you got responsibilities and you got to feed your children and so forth and protect them. And so your prefrontal cortex is fully online. You're very goal focused, productive and memory is serving this purpose that's very focused. Now you get older and your function is not in traditional societies has never been ... Once you passed your child-rearing years, your goal is to really be providing knowledge and wisdom to younger generations. And so it's not about your goals, which is what the prefrontal cortex is really trying to get you to focus on, but really about those around you and preserving wisdom.
And if you look at aging semantic knowledge or knowledge about the world actually remains remarkably solid, or if anything even improves as people get older. So it's not that aging is associated with just this loss of function, it's just a change. And I think that really has given me an appreciation, again for the ecology of memory and how our memories are shared with others, how we build memories from other people, and I think that was the biggest change, and even writing my personal stories gave me that sense too.

Dr. Correa:
Well, thank you so much for helping us connect with that sense of community importance of all varieties of perspectives. The different members in our community, how that invests particularly into our own memories and how we can invest intentionally into our own memories and our relationships. It's been great having a talk together and really enjoyed the book. We'll have more details about his book, why we Remember and Dr. Charan Ranganath in the show notes, so please make sure to check that out. Thank you so much for joining us.

Charan Ranganath:
Thank you. It's been great to be here.

Dr. Correa:
Thank you again for joining us today on The Brain & Life Podcast. Follow and subscribe to this podcast so you don't miss our weekly episodes. You can also sign up to receive the Brain & Life magazine for free at brainandlife.org.

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Dr. Correa:
You can also find that information in our show notes, and you can follow Katy and me and the Brain & Life magazine on many of your preferred social media channels. We are your hosts, Dr. Daniel Correa, connecting with you from New York City and online at Neuro Dr. Correa.

Dr. Peters:
And Dr. Katy Peters joining you from Durham, North Carolina and online at Katy Peters MD PhD.

Dr. Correa:
Most importantly, thank you and all of our community members that us with their health and everyone living with neurologic conditions.

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Why We Remember with Neuroscientist Charan Ranganath

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