When is forgetting normal — and when is it worrisome? A neuroscientist weighs in

Do you have trouble remembering names or where you put your keys? Neurologist Charan Ranganath, author of Why We Remember, talks about the science of memory. Originally broadcast Feb. 24, 2024.

Transcript

DAVID BIANCULLI, HOST:

This is FRESH AIR. I'm David Bianculli. Do you ever walk into a room and forget why you're there, or read a book or watch a movie and years later can't remember a thing about them? Charan Ranganath is a neurologist who studies memory, and what he's about to say might make you feel better about your memory. When Ranganath meets someone, the question he's most often asked is, why am I so forgetful? He says we have the wrong expectations for what memory is for.

The mechanisms of memory, he says, were not cobbled together to help us remember the name of that guy we met at that thing. Instead of asking, why do we forget, we should really be asking, why do we remember? And that's the question he's been researching for about 25 years with the help of brain imaging techniques. Charan Ranganath directs the Dynamic Memory Lab at the University of California, Davis, where he's a professor at the Center for Neuroscience and the Department of Psychology. His book is called "Why We Remember," and it's out in paperback. Terry Gross spoke with him last year.

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TERRY GROSS: Charan Ranganath, welcome to FRESH AIR. It's a pleasure to have you here. I learned so much about memory. I want to tell you, I've had proper noun issues for years or decades. And sometimes, if anything that starts with a capital letter - a person's name, a movie, a television show, a recording, the songwriter's name (laughter) - I'll remember the lyrics, but not who wrote it, even though I know who wrote it. And I know the name of the movie, and I know the name of the show, and I can't find it in my brain. And then a few seconds or a few minutes or a few hours or a few days later, without even thinking about it, it just kind of pops into my mind. What is going on?

CHARAN RANGANATH: I really find this a fascinating phenomenon. They call it the tip-of-the-tongue phenomenon sometimes. I don't know if this is what you're talking about.

GROSS: Yes.

RANGANATH: But where you have - you know the information is there. And, I mean, you're aware of something, but it just doesn't - you don't have proof of its existence. You're just working on this complete faith that it exists. There's many reasons why this happens. One of the big ones is you pull out the wrong information. When you pull out the wrong information, what happens is it makes it much harder to find the right information. So in other words, if you're looking for someone named Fred (ph) and you accidentally pull out Frank (ph), you know that's not the name. Now Frank is very big in your consciousness, and it's fighting against the other memory that you have. And so as a result, you're going to have some trouble. Now, later on, what happens is your mindset changes, and you're no longer stuck in that previous mistake. And that's why it can pop up. So what can sometimes happen is, is that we get - we're looking for something, but then we get the wrong thing. And that leads us so far in the wrong direction that the competition in memory works against us.

GROSS: But sometimes I know that the name starts with a K or it starts with an L. Why do I know that, but I don't know the name?

RANGANATH: Well, that's another thing that can happen, is that you get what's called partial retrieval, where you get a piece of the information but not the whole thing. And again, you know, one of the things that I talk about in the book is this idea that - and I realized as I was writing it that it's not very intuitive, but memories compete with each other. And this is true for a name. This could be true for a memory for an event. And so if you have learned multiple names that start with the letter K, now what happens is you have this competition where essentially they're fighting with each other.

GROSS: Oh, I go through the whole alphabet. Is it Ka (ph)?

RANGANATH: (Laughter).

GROSS: Ke (ph), Ko (ph). (Laughter) You know?

RANGANATH: Yeah, and the more similar they are, the harder that competition is, right?

GROSS: Yeah.

RANGANATH: And I want to be clear that proper nouns are exceptionally hard because they're not - the problem is never the name, or usually not the name. With me, it's sometimes - with my name, it's the name for people. But let's say if the person you're looking for is Katherine - right? - starts with a K. The problem is, is that there's nothing that helps you link Katherine's name with her face. It's just a completely arbitrary link, right? They could look like anyone, and that would be their name. So you're really trying to form a memory for something that's utterly meaningless, and that's the hard part. It's a little bit easier if you have some knowledge about them, but often it's just very hard. And even once you learn it, as you said, you can still suffer from this competition because there's many other people that you have probably met whose name also starts with a K.

GROSS: Well, you make an interesting distinction, which is that there's a difference between forgetting and a retrieval failure. And, like, for instance, my proper noun problem is a retrieval failure 'cause it's in there, it's in my brain someplace; I just can't find it. It's like rummaging through the junk drawer (laughter) to find something really small.

RANGANATH: That's exactly - that's one of the best analogies that I would think of is rummaging through the junk drawer, right? Another example I could give, which is - it's easy for me to think of because it's my life - is that, you know, if I walk into my desk in my office, it's completely filled with junk. My desk is my junk drawer, basically. And I'm looking for something, let's say. And let's just imagine I have a hundred Post-it notes on my desk and they're all yellow. And on one of them, I wrote my password for some bank account, let's say. I'm looking and I'm looking. It's going to take me a while to find it, and I might not find it amidst all the other clutter. But if I had used a hot pink Post-it note, it would stick out relative to everything else. And that is the issue with memory, is you want something that's distinctive, that makes this particular memory unique relative to other memories that you're looking for, right? And so that's a big part of what helps you overcome the competition in memory.

GROSS: But you can't do that with every memory. I mean, it's like having a new password every time (laughter) you sign onto a site. There's a limit to how many mnemonic devices or, you know, like, little memory tricks you can use for every password. And add to that everything you want to remember. How many memory devices can you come up with?

RANGANATH: Well, I think this is one of the reasons why I wanted to write this book so badly. I'd been told by a lot of people, hey, you should write a book teaching people how to remember more. And I always say, you don't want to remember more, you want to remember better because nobody that's ever been studied has a photographic memory for everything. And in fact, I don't care because my phone has a photographic memory, literally. I don't need to do that.

GROSS: I want to ask you about social media because so many people are constantly, like, jumping from one post to another, from one screen to another. And, you know, attention spans on screens are getting shorter and shorter. How does it affect your memory of what you've seen on social media if you just keep scrolling, and does that have an impact on your general ability to remember? Like, if your attention...

RANGANATH: I think...

GROSS: ...Is constantly getting diverted from one thing to another, one thing to another, does that have a - you know, a sustained effect?

RANGANATH: Yes. I think that the technology in and of itself doesn't necessarily cause these changes. It's more how we interact with the technology. And what I mean by that is that if we are switching between one thing and another and we're so in the habit of being responsive to everything, what happens is, is that you have two problems with this. So one is, is that your attention actually gets grabbed every time you switch. You actually have a little bit of a cost. And your prefrontal cortex for - you know, just to simplify, it has to work a little bit harder just to get you caught up and back on the program, right? So I'm, right now, looking - I'm doing a social media post, but then I'm Instagramming my time at this cafe, and then I'm going back and talking to my wife. Every time I switch back and forth, my brain uses some resources just to get on task. So I'm already behind schedule once I switch over, and as a result, I'm a little bit more - I'm even stressed. I'm behind, and I'm having trouble focusing in a way that allows me to get these sharp memories because the memories that stick around are going to be the ones where we have a lot of rich information about the sights and the sounds, and just - they're more of the immersive sensory details that can really make this moment unique relative to all these other moments.

And so other things that we do with social media and the way we interact with it, like taking pictures, for instance, sort of the rise of Instagram walls everywhere, you can see now how much that has changed people's experience of places. And as a result, what I think sometimes happens is that people get into a mode of mindlessly taking pictures in a way that doesn't focus them on the details of their surroundings. And what do you do? You post it. You get a lot of these pictures. You overdocument, and then you post them and either never go back to them or, in the worst case, they disappear, right? So there's a platform called Snapchat where the information literally disappears within - I don't know - 24 or 48 hours. And I think that's a metaphor for how technology can impact our memories in general.

BIANCULLI: Neurologist Charan Ranganath speaking with Terry Gross last year. We'll be right back. This is FRESH AIR.

This is FRESH AIR. Let's get back to Terry's interview from last year with neurologist Charan Ranganath. He's the author of "Why We Remember," which is now out in paperback.

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GROSS: There are memories that we'd like to forget but we can't. And that's mostly, like, traumatic memories, especially PTSD or memories of, you know, sexual abuse, rape, crime. And when we have an experience like that, a traumatic experience, the fight-or-flight response kicks in whether or not we can actually fight or flight. So what's going on chemically in the brain with that fight-or-flight experience that makes a bigger, like, a deeper, unforgettable kind of memory?

RANGANATH: Well, there's two parts of it, right? So there's this fight-or-flight response, which is - we tend to associate with the feeling of fear. And so that's our heart racing. Our body is mobilizing us to move. And so we're getting - adrenaline's pumping through our veins. And we have a burst of a neuromodulator called noradrenaline in our brains. And that's going to promote plasticity for this moment when I was scared for whatever it happens to be. And so that's the brain's saying, hey, this is biologically important.

But we also have the anxiety of how things could happen. So in other words, if you're a mouse and you're running around, and all of a sudden you see a cat and the cat starts chasing you, you get this big fight-or-flight response. But now you could be a mouse, and you don't know where the cat is, but it's somewhere out there, and any moment, it could jump out. Now you're under stress and anxiety. And that's associated with all these release of these stress hormones. And the way these stress hormones tend to work is they don't just enhance memory for that moment where the bad thing happened, but a lot of the things leading up to it. And we think the reason for that - I think it makes sense - is if you're a cave person and you go into a cave and you get attacked by a saber-tooth tiger, you don't want to just know that you got attacked by the saber-tooth tiger. You want to know where that cave was and how to avoid it in the future. So you want to learn all the things that led up to that point. And so that's one of the ways in which these traumatic experiences can hijack those survival circuits that we have.

GROSS: So once you have what seems like an indelible, horrible memory and things that are happening now make those memories come to the surface again and you're deep into post-traumatic stress disorder, how does our knowledge of that perhaps help in changing the trauma of reexperiencing the traumatic event?

RANGANATH: Well, part of the vividness that we have when we recall a traumatic event - and this is true in PTSD and in people who don't have PTSD but are remembering something traumatic - is that you get this visceral response. And that's that kind of - you get a reactivation of the stress response or the fight-or-flight response where your heart starts racing. You may be sweating or something like that. And that actually gives us that feeling of vivid remembering. Even though we're not getting the details of what happened often, it just makes us feel like we're remembering more. And I think one of the important things that we used to do when I was doing my clinical training was actually do cognitive behavioral therapy. And the behavioral therapy was addressing this kind of more visceral response associated with the fear. But then there's the how you think about it part, and the thinking about it part is actually separate. And it involves getting people to not just - not change the memory per se, but change how you interpret it and how you think about it.

GROSS: Can you explain that a little bit more? 'Cause I know early in your career or in your studies, you were working with veterans. And it was kind of like a group therapy session that you were running, and they were dealing with these kind of traumatic memories from their time, I think, mostly in Iraq. So how did the technique that you're talking about of changing the narrative that you tell yourself about that story - how did that go? How did that work?

RANGANATH: In our group, we had both veterans of the Vietnam War, but also the Iraq wars. And so I came into this group cold, thinking to myself, you know, I'm a young psychology intern. I don't have any of these experiences. What am I going to do? And what I realized was I had this hugely important role to be a team member with them. It wasn't like they were my patients. Like, we were working as a team where one person would release this memory that they just hadn't shared before, and another person would release a memory. And next thing you know, I could see this shared narrative build up that was common across all these people. But because I wasn't in the thick of it, I could view it from a bird's-eye view and give them a different perspective on it.

And as we would come to an agreement about the way to reinterpret this memory, those memories are being transformed little by little because the act of recalling them and sharing them changes it. So you tell me a memory, and it's no longer your memory. It's our memory because of the work that we put into in terms of transforming it.

GROSS: So how does that make things any better?

RANGANATH: Well, I think that there's events that we experience that are objectively bad. But what do we take away from those experiences, right? Sometimes they're learning experiences where we would say, OK, I don't want to make that mistake again. There's something we can look at and learn from and take with us into the future. Sometimes there's things that are just - bad things happen to people. But even then, you learn from your resilience, and you learn that you survived those experiences. And so, you know, I've had experiences like that myself. And I think that act of changing the way you look at the past makes you realize that it's not an objective thing. The way we look at the memory is going to affect how we feel about it.

GROSS: And as you've pointed out, like, memories change over time. Memories aren't, like, indelibly the same. You compare it to, like, a copy machine and making a copy of a copy of a copy. The image gets lighter. It can change - you know, change slightly. And it's no longer like the original. So what you're talking about is having that work in your favor.

RANGANATH: That's right. That's right. But what I would say is that we can even - it's not like you're fundamentally changing necessarily your recall of what happened. But when we look at memories from a different perspective, we can often see different things. You can actually pull up parts of the memory that you didn't even know were there before, right? So it's not necessarily distorting your memory, but changing your perspective. But that in and of itself now changes that narrative that you've started to put together. So the story is part of how we approach that past. And building that new story changes our default way, so to speak, of imagining how that thing could have been.

GROSS: You write that sleep is very important both to memory and to synthesizing memory. Can you tell us, you know, briefly what goes on in the brain while we're sleeping that is so helpful?

RANGANATH: Well, one of the fascinating things about sleep is we tend to think, oh, nothing's happening. I'm not getting anything done. But your brain is hugely at work. There are all these different stages of sleep where you can see these symphony of waves where different parts of the brain are talking to each other, essentially. And so we know for a fact that one of - at some of these stages of sleep, what happens is the brain will flush out toxins, like the amyloid protein that can build up over the course of a day. So just by virtue of that function, sleep is very important.

But then on top of it, what we can see is that the neurons that were active during a particular experience we have come back alive during sleep. And so there seems to be some processing of memories that happen during sleep, and that - the processing of memories can sometimes lead to some parts of the memory being strengthened, or sometimes you're better able to integrate what happened recently with things that happened in the past. And so sleep scientist Matt Walker likes to say that sleep converts memory into wisdom, for instance.

GROSS: So we should really give ourselves time to sleep, even when we feel like we don't have the time.

RANGANATH: Absolutely, because it's an investment because you're depriving your brain of all this information processing that can happen in your sleep, and I do believe that - it's controversial, but I do believe in the idea that sometimes you can wake up and through that memory processing actually have the ability to solve a problem that you couldn't do when you were - before you went to sleep. I mean, the other part of sleep, I think that's very important, is when we're sleep deprived, it's just terrible for memory. All the circuitry that's important for memory does not function as well. And memory performance really declines.

GROSS: Do you get enough sleep?

RANGANATH: No.

(LAUGHTER)

RANGANATH: Not at all. Not at all. No. I wake up in the middle of the night, and I'm still trying to figure out exactly why.

GROSS: Right. So we all have problems, I think it's fair to say, remembering names and faces. It's very common. And it's really embarrassing when it happens, especially if it's someone whose name you really ought to have remembered. I'm confident that this has happened to you. And it must be especially embarrassing because you are a memory scientist. So how do you deal with it when you - especially if you're supposed to be introducing this person to somebody else and you can't even remember their name, how do you deal both with the embarrassment of it and just with the, you know, not wanting to hurt somebody's feelings by making them feel not important enough to have remembered their name? Like, what's your cover?

RANGANATH: Oh, my God. I still am working on this. I've had so many gaffes with people who I've known for so long, and I'm just terrible at this. The only thing that I have going for me is that people can just tell within an instant that I'm absent-minded. And especially once I tell people I study memory, that gets me off the hook because you tend to study what you're not good at, right? So they call it me-search (ph). And so I think there's kind of a general idea that you study the things you're not good at, which is why I'm always a little suspicious of the social psychologists (laughter).

GROSS: Charan Ranganath, thank you so much for talking with us.

RANGANATH: Thank you. This has been fantastic.

BIANCULLI: Charan Ranganath, author of the book "Why We Remember." He spoke to Terry Gross last year. Later, we listen back to our 1997 interview with Alf Clausen, the Emmy-winning former composer, arranger and orchestrator for "The Simpsons." Justin Chang reviews the new film "The Life Of Chuck," based on a Stephen King novella. And I provide some context for the upcoming live TV performance of George Clooney's Broadway production "Good Night, And Good Luck." I'm David Bianculli, and this is FRESH AIR.

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