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MIKE PESCA, host:

So we have a new segment, an interesting segment, I just - it's driving me crazy. I cannot remember what it's about. It is on the tip of my tongue. What is the word for this?

RACHEL MARTIN, host:

It's phenylalanine.

PESCA: No, no, no. That is the stuff in soda that phenylketonurics can't drink. What is the word I'm trying to think of?

MARTIN: Geep (ph).

PESCA: No, actually, that's a mythical-goat-sheep hybrid. Oh, well, I can't think of it. Never mind. Instead, let's bring on this guy who wrote a great article in the Boston Globe, all about tip-of-the-tongue moments. Ah, we were being met out. We really knew what was going on.

MARTIN: Ah, so met out.

PESCA: Yeah. New research about these moments is leading scientists to change the way they think about brains and memory. So we're going to play Ripped Off...

(Soundbite of "Law & Order" theme)

PESCA: From the Headlines. Joining us now is Jonah Lehrer, editor at large of Seed Magazine and author of "Proust Was a Neuroscientist." Hey, Jonah.

Mr. JONAH LEHRER (Editor at Large, Seed Magazine; Author, "Proust Was a Neuroscientist"): Hey, thanks so much for having me.

PESCA: You - we're glad to have you, because this is such an interesting phenomenon that we've all had. But what's new is, I guess, somehow researchers are able to look at tip-of-the-tongue moments more than they ever have before. Explain that, if you would.

Mr. LEHRER: Yeah, it's this frustrating and universal phenomenon, a human experience. It happens on average about once a week, a little bit more if you're older. And now, I think, in the last couple of years, for the first time, scientists have been able to see what happens in your brain when you have these tip-of-the-tongue moments.

PESCA: You mean with imaging? How have they been able to look at that?

Mr. LEHRER: Yeah, with brain scanners, with fMRI machines. And they use this kind of nifty experimental paradigm, where they give you the definition of a word that's somewhat obscure, like contraband. They'll ask you if you know the word and most people say, yeah, I know that word, and then one to two percent of the time, people have a tip-of-the-tongue moment. They'll know the word, but they can't produce the word. And so that's how they generate these phenomena pretty reliably in the lab.

PESCA: So it actually works backwards, right? You would say, what's the word for, of, or relating to a fox?

Mr. LEHRER: Yes.

PESCA: And then you would say, oh wait, I know, I know. And then it turns out, hey, it's vulpine, but it was on the tip of your tongue. And as I was thinking about that, they - you'd be looking at my brain and what would you see?

Mr. LEHRER: Well, what - the first thing you'd see is the frontal lobes get activated, specific parts of the frontal lobe. And this is the brain searching its own database for that word. The brain is saying, I know that word is in here somewhere, you know, I know I know the definition of that word, and yet I can't find the word.

PESCA: Uh-huh.

Mr. LEHRER: And you see the brain searching itself, this frantic, manic process. The brain is very upset, because it can't find what it certainly knows, and that's what you see in this brain scanner. It's a unique talent called metacognition.

PESCA: Metacognition.

Mr. LEHRER: Metacognition. So, you know, the invocation of meta was spot on.

PESCA: Yeah.

Mr. LEHRER: And that seems to be this process whereby the brain can think about how it thinks.

PESCA: Metacognition means thinking about thinking.

Mr. LEHRER: Exactly.

PESCA: And I guess the people who studied metacognition are meta-metacognition researchers.

(Soundbite of laughter)

PESCA: But so, is it just, like, we're going - we flip through it like a rolodex? What are we do - go in alphabetical order, trying to find a word that we can't quite place, is that how it works?

Mr. LEHRER: The old model of memory we had, the brain was like this vast file cabinet, so everything you knew from words to names to, you know, kind of random facts were all stored in this perfect logical order, you understand? Immaculate, huge, instant file cabinet. And now I think, thanks to things like the tip-of-the-tongue research, scientists realizing that the brain isn't like a file cabinet at all. It's much more like a very, very messy desk, cluttered with big piles of paper.

And so when you misplace a name or a word, what you're doing is frantically searching your desk, kind of trying to find the one piece of paper amid all these billions and billions of piles of paper that - you know, that is the one word you're looking for. So that's what they're seeing in a brain scanner, the brain kind of searching its own mess, trying to find the word.

MARTIN: Jonah, does everyone go about that search in the same way? Or does one person go through that stuff on their brain desk in the order of experiences, what happened most recently, to what happened further away in time? Or do other people do it based on the alphabet or something? Does everyone go about that process of the search the same way?

Mr. LEHRER: Well, people seem to rely on the same brain regions. The one interesting thing is that the nature of the search changes with age. So as you age, your frontal lobes, the frontal cortex, prefrontal cortex, and the interior singular cortex, they tend to shrink in volume and lose some density. So it becomes harder to search your own brain. So I think most people think that when you lose memory with age, what happens is the memories disappear, they vanish.

What seems to actually be happening, this is why tip-of-the-tongue moments become more common, is that the memories might still be there, you just can't find them. Because the search mechanism in your own brain has been degraded, it's this kind of paradoxical moment where, you know, the memories are right there. There still in your brain. Your neurons are still remembering the name of that person you just met on the street, and yet, your brain just can't find that name, because your frontal lobes have kind of shrunk a little bit.

PESCA: It's interesting, in your article, you write about the ways we actually get to the actual word are sometimes - seem really roundabout. Like, you can remind someone of a word that almost sounds like the word, and somehow they'll be able to recognize that. How does that work?

Mr. LEHRER: Yeah. Well, researchers are also using tip-of-the-tongue moments to study how language is connected in the brain.

PESCA: Uh-huh.

Mr. LEHRER: So, and it shows that language is very interconnected in the brain. So, for example, typically the reason - one of the main reasons we resolved the tip-of-the-tongue moment, you know, the word simply pops into our head an hour later. We remember the movie we were trying to find at Netflix, is that we encounter another word with the same first syllable. And so then that network of neurons in the brain that encodes the word that we're trying to remember is activated, and the word pops into our head. So, if we're trying to remember contraband, we encounter another word with C-O-N as the first syllable.

PESCA: Yeah.

Mr. LEHRER: It turns out you can also trigger similar things by giving someone a word that reminds them of another word, that also shares that first syllable. So if you're trying to remember the word - you know, a word, bike, and you give someone just, like, a motorcycle, that obviously will...

PESCA: Right. That's pretty spot on. A motorcycle looks like a bike.

Mr. LEHRER: Exactly.

PESCA: But you could also show them - what?

Mr. LEHRER: Well, let's say they're also trying to remember another word that shares the first syllable as bike.

PESCA: Right.

Mr. LEHRER: So you...

PESCA: So you could show them a tumor, they would think of biopsy, and biopsy is like bike, and then they get it that way.

Mr. LEHRER: Exactly.

MARTIN: Wow.

PESCA: Interesting. And so is there any evolutionary advantage to having this somewhat messy desk, the disorganized brain?

Mr. LEHRER: I'm not going to call it an advantage. It's only a byproduct of evolution. The fact is natural selection's a hacker, not an engineer, and so our brain is not always designed in the most logical way possible. But you know, (unintelligible) thing - one researcher I talked to said, you know, if the brain wasn't so messy, we might not be so creative.

MARTIN: Mm.

Mr. LEHRER: That the messiness is also, you know, allows us to find those serendipitous connections that we don't expect to connect. So the messiness isn't all bad.

PESCA: Yeah, it's like those - you know the story. After 9/11, the old FBI computers couldn't search for two terms at once. Like, it knew "terrorist," and it knew "flight school," but it couldn't connect them, so our brains are better than the FBI computers.

(Soundbite of laughter)

Mr. LEHRER: Yes, when I think too much.

PESCA: Yes.

Mr. LEHRER: But no. It is pretty astonishing in that respect, how rare tip-of-the-tongue moments are, considering all the stuff we have crammed into our head. And the fact that it only happens once or twice a week, that, to me, is pretty impressive.

MARTIN: But man, when it happens, it is infuriating.

Mr. LEHRER: It really is.

PESCA: And what's interesting, and the last very interesting fact, all languages, or many, many languages, have a phrase for this, and it's almost always something like tip-of-the-tongue.

Mr. LEHRER: Yeah, that is just one of the bizarre things. Even the scientists I talked to couldn't really explain why that is.

PESCA: That's great. Jonah Lehrer, editor at large at Seed Magazine and author of "Proust Was a Neuroscientist." And I guess the subtitle could be, what? "Nature is a hacker, not an engineer." Is that what you just said to me?

MARTIN: That was nice. That's lovely.

PESCA: Yeah. Great quote. All right. Thanks, Jonah.

MARTIN: Thanks, Jonah.

Mr. LEHRER: Thank you.

MARTIN: Coming up next on the big show. Liz Phair talks about her album, "Exile in Guyville." It's been 15 years since she made that, do you believe it? Coming up next on the BPP from NPR News.

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