Rebecca Saxe: How Do We Know What Other People Are Thinking? Sensing the motives and feelings of others is a natural talent for humans. But how do we do it? Neuroscientist Rebecca Saxe explains how one region in the brain focuses on other people's thoughts.
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How Do We Know What Other People Are Thinking?

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How Do We Know What Other People Are Thinking?

How Do We Know What Other People Are Thinking?

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It's the TED Radio Hour from NPR. I'm Guy Raz. And today on the show, we're asking...

REBECCA SAXE: How patterns of electrical pulses passing between cells in an organ in your body can be thought.

RAZ: Or, you know, how does the brain work, make us who we are?

SAXE: (Laughter).

RAZ: An almost impossible question maybe, but one that totally...

SAXE: Totally.

RAZ: ...Excites Rebecca Saxe.

SAXE: Could you think of anything better?

RAZ: Rebecca is a neuroscientist at MIT. She's actually worked with Nancy Kanwisher there, who we just heard from. But while Nancy studies how the brain recognizes faces...

SAXE: I study, how does the brain figure out what somebody else is thinking?

RAZ: So how does it happen?

SAXE: (Laughter). Well, here's one way of thinking about it.


SAXE: You're watching "Romeo And Juliet."


SAXE: And you see Juliet wakes up.


UNIDENTIFIED ACTRESS: (As Juliet) Oh, comfortable friar.

SAXE: She can't see Romeo yet.


UNIDENTIFIED ACTRESS: (As Juliet) Where is my lord?

SAXE: So right now, what's going on in her mind? She knows that she's in a mausoleum.


UNIDENTIFIED ACTRESS: (As Juliet) I do remember well where I should be, and there I am.

SAXE: She knows she's not dead, but that everybody thinks she's dead.


UNIDENTIFIED ACTRESS: (As Juliet) Where is my Romeo?

SAXE: And right now what she thinks is everything's worked out. The whole plan has worked.

RAZ: Yeah.

SAXE: So now imagine you're in the audience watching that, and you see Juliet. You know what she's thinking - everything's going to be fine. I get to marry Romeo and run away, and it all worked. But you also know that she's totally devastatingly wrong.


UNIDENTIFIED ACTOR: (As Friar Lawrence) Lady, come from this nest of death, contagion and unnatural sleep.

SAXE: Romeo is already dead. It's already too late.


UNIDENTIFIED ACTOR: (As Friar Lawrence) Come, come away. Thy husband in thy bosom there lies dead.

SAXE: So huge parts of your brain are devoted to solving just those problems - knowing where the girl is, knowing what words she's saying, knowing what those sentences mean.


UNIDENTIFIED ACTRESS: (As Juliet) Cup closed in my true love's hand? Poison, I see, hath been his timeless end.

SAXE: But all of that gets processed and processed through many, many, many different brain regions until you distill it down to this one more complicated problem, above and beyond the words and the images, is the set of meanings that are about her thoughts and feelings. So how does the brain do that?

RAZ: Yeah?

SAXE: Fifteen years ago, when I started in this field, it wasn't clear you could ask that question as a scientist and that, to me, that's kind of the miraculous thing. It's not that there is an answer, it's that the very limited tools we have now for studying the brain are enough to let us make a little bit of progress.

RAZ: And Rebecca is slowly making progress on the central question of her work - how can one brain know another? Here she is on the TED stage.


SAXE: And put another way, the crux of the problem is the machine that we use for thinking about other minds, our brain, is made up of pieces, brain cells, that we share with all other animals, with monkeys and mice and even sea slugs. And yet, you put them together in a particular network and what you get is the capacity to write "Romeo And Juliet." Or to say as Alan Greenspan did, I know you think you understand what you thought I said, but I'm not sure you realize that what you heard is not what I meant.


SAXE: So first, the first thing I want to tell you is that there's a brain region in the human brain, in your brains, whose job it is to think about other people's thoughts. It's called the right temporoparietal junction. It' above and behind your right ear, and you don't use it for solving any other kinds of logical problems. The second thing I want to say about this brain system is that although we human adults are really good at understanding other minds, we weren't always that way. It takes children a long time to break into this system, and I'm going to show you a little bit of that long, extended process. The first thing I'm going to show you is a change between age 3 and 5, as kids learn to understand that somebody else can have beliefs that are different from their own. So I'm going to show you a 5-year-old who's getting a standard kind of puzzle that we call the false belief task.

RAZ: The false belief task is a way of measuring how well a child can think about someone else's thoughts. Rebecca showed us a video of the task, which involves a 5-year-old and a puppet show starring two pirates.


SAXE: This is the first pirate. His name is Ivan. And you know what pirates really like?


SAXE: Pirates really like cheese sandwiches.

UNIDENTIFIED CHILD: Cheese? I love cheese.

SAXE: Yeah.

RAZ: Oh, yes.

SAXE: Yeah, all pirates love cheese sandwiches.

RAZ: Yes.

SAXE: (Laughter). So...

RAZ: Anyway, here's what's happening. The first pirate, Ivan, puts his cheese sandwich down on a treasure chest. But then he realizes he forgot his drink to go with the sandwich.


SAXE: And so Ivan goes to get a drink. And while Ivan is away, the wind comes (imitates wind), and it blows the sandwich down onto the grass. And now here comes the other pirate. This pirate is called Joshua. See? And Joshua also really loves cheese sandwiches.

RAZ: OK. So then Joshua, the second pirate, he also has a cheese sandwich - his own sandwich.


SAXE: And he says, yum, yum, yum, yum, yum. I love cheese sandwiches.

RAZ: But he puts his down on the treasure chest as well.

SAXE: So now we have two cheese sandwiches. Ivan's, which is now on the ground, and Joshua's, which is now sitting on top of the treasure chest.


UNIDENTIFIED CHILD: So that one is his.

SAXE: That one's Joshua's. That's right.

UNIDENTIFIED CHILD: And then his went on the ground.

SAXE: Yeah, that's exactly right. Now...

UNIDENTIFIED CHILD: So he won't know which one is his.

RAZ: And then...

SAXE: The key thing that happens is.

RAZ: ...The first pirate...

SAXE: Actually I can't remember who's the first pirate. Is the first one Ivan?

RAZ: I think Ivan...

SAXE: Or Joshua?

RAZ: I think Ivan's the first one.

SAXE: (Laughter). Sorry.

RAZ: Ivan is the first one, yes.

Ivan, the first pirate, he comes back.


SAXE: And he says, I want my cheese sandwich. So which one do you think Ivan's going to take?

UNIDENTIFIED CHILD: I think he's going to take that one.

SAXE: Yeah, you think he's going to take that one? All right, let's see.


SAXE: Oh, yeah. You we're right. He took that one.

RAZ: Ivan, of course, takes the clean sandwich on the chest 'cause that's where he left it.

SAXE: That's what he thinks.

RAZ: That's what he thinks.

SAXE: Right.

RAZ: And that's the conclusion you'd reach if you're 5 or 10 or 50.

SAXE: But a 3-year-old can't quite work that out.

RAZ: In fact, if you are 3, you fail this test.

SAXE: Yeah.

RAZ: Because you can't quite understand what the first pirate was thinking.

SAXE: Can't work out that he could have beliefs different from reality.

RAZ: Your average 3-year-old can't quite process the idea that another person can think different thoughts, but a 5-year-old can. And although we know that something happens between the ages of 3 and 5 in that little patch of brain that Rebecca studies, we still don't know what.

SAXE: That little patch of brain is made up of millions of neurons. But it's like if you were looking down at Iowa from an airliner. There's all these fields. And inside the fields are plants. And the individual plants are growing their individual ears of corn. Well, you can't see the ears of corn. You can't see the plants. But you can see the fields. And you can see that some of the fields are a little brighter green and some of them are a little darker green. So we're looking at the brain from an airliner, and we can see the difference that in some kids, you can see - OK, bright patch over there, darker patch over there. And in other kids, it's pretty much all the same color all over the fields.

RAZ: And so the challenge of modern neuroscience is to try and figure out how we can see the kernels of corn in those fields, not just the colors they add up to. But Rebecca says even knowing where those fields are, that's a huge leap forward in what we know about the brain.

SAXE: Yeah, because this science is so hard. Most ideas don't work for a million reasons, that when you have a theory and a prediction and a method and you think, if I'm on to something, I know what to expect here, and that happens, that's kind of amazing.

RAZ: Rebecca Saxe runs Saxelab. It's a neuroscience lab at MIT. Her full talk is at

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