Mirror Neurons

PBS air date: January 25, 2005

ROBERT KRULWICH: Hello again. Gaze into a mirror, and what do you see? Well, I see my face, of course. But in my face I see moods, I see shifts of feeling.

We humans are really good at reading faces and bodies. 'Cause if I can look at you and feel what you're feeling, I can learn from you, connect to you, I can love you. Empathy is one of our finer traits, and when it happens it happens so easily, perhaps because—and this is brand new science, this is just out of the lab—we may have some special circuitry in our brains that helps us whenever we look at each other.

Ask yourself, "Why do people get so involved, so deeply, deeply involved, with such anguish, such pain, such nail biting tension over football?"

COMMENTATOR: The Cleveland Browns are gambling on defense.

ROBERT KRULWICH: Why are we such suckers for sports? And it's not just sports. We can lose it completely at the movies, at video games, watching a dance. Is there something about humans, humans particularly, that allows us to connect so deeply when we watch other people—watch them moving, watch them playing, watch their faces?

Well, as it happens, scientists have an explanation for this strange ability to connect. It's new.

DANIEL GLASER: It had never been found on a cellular level before.

ROBERT KRULWICH: A set of brain cells, found on either side of the head, among all the billions of long branching cells in our brain, these so-called "mirror neurons," have surprising power.

DANIEL GLASER: What we've found is the mechanism that underlies something which is absolutely fundamental to the way that we see other people in the world.

ROBERT KRULWICH: And it began entirely by accident, at a laboratory in the lovely old city of Parma, Italy, where a group of brain researchers was working with monkeys, and they were testing a neuron—that's a brain cell—that always fired...made this sound...

(NEURON FIRING): Clack, clack, clack.

ROBERT KRULWICH: ...whenever the monkey would grab for a peanut. So the lab had all these peanuts around, and whenever the monkey made its move...

(NEURON FIRING): Clack, clack, clack.

ROBERT KRULWICH: ...the neuron would fire.

Scientists thought, "Now here's a neuron that's essential to motion. It's a motor neuron."

Then, one day, the monkey was just sitting around, not moving at all, just sitting, when a human scientist came into the lab. And when that scientist grasped the peanut? Yeah, the monkey's cell fired.

Now, the monkey hadn't moved, it was the human that had moved, suggesting that this neuron up here couldn't tell the difference between seeing something and doing something—seeing and doing were the same—or more intriguingly, that for this neuron, watching somebody do something is just like doing it yourself.

The head of the lab, Giacomo Rizzolatti, thought, "Wow!"

GIACOMO RIZZOLATTI (University of Parma): The same neurons, one neuron, fired, both when the monkey observed something, and when the monkey is doing something. It is almost unbelievable.

DANIEL GLASER: It was surprising, because this cell, which was involved with motor planning for the monkey, turned out to be interested in the movements of other people as well.

ROBERT KRULWICH: Some people call them "monkey see, monkey do" neurons, but the name that stuck is "mirror neurons," because with them, the brain seems to mirror the movements it sees.

This accidental discovery got scientists thinking, doing more tests, and soon it came pretty clear that this is not just a monkey thing, it's a people thing, too.

We all know that humans learn by looking and copying; that's what infants do.

First you look...

MOTHER: One, two, three, four.

ROBERT KRULWICH: ...then you do.

DONNA: Ready? Let's see your feet this way.

ROBERT KRULWICH: And once you've watched and copied and learned a set of moves, you not only have them in your head, if you see somebody else doing it you can share the experience. They know the moves, you know the moves, so you can move with them.

DANIEL GLASER: If you can use the years of training that you, yourself, have done—learning to crawl, then learning to walk, then learning to eat—this is an incredibly rich set of knowledge that you could apply to the problem of actually seeing what's going on.

ROBERT KRULWICH: So that's why, when I head down the street carrying all these packages, not only do people watch, look how they're watching.

They feel my predicament because they know what it's like to carry heavy packages. They know all about "carrying." So as they watch me moving they can feel themselves moving. Their neurons are "mirroring" the action.

These neurons may be the brain's way of translating what we see so we can relate to the world.

DANIEL GLASER: The mirror system is the way that you tap into...the way that you harness your own abilities and project them out into the world.

ROBERT KRULWICH: And people are really good at watching and translating what we see. Like, with just thirteen moving dots—that's all there are here—you'll have no trouble recognizing these very ordinary activities. What's more, tests have shown that when a person sees a movie like this of his own movement, he'll recognize it immediately as his own.

And that's why sports fans tense with the action, and wince, and leap. 'Cause if you know the game...

FOOTBALL FAN 1: Flag! Flag!

FOOTBALL FAN 2: No, no, no flag.

FOOTBALL FAN: No flag.

ROBERT KRULWICH: ...then your neurons are firing as if it's you playing, giving whole new meaning to the phrase "armchair quarterback." That's why it's so easy to be a sports fan.

But there is more, suggests U.C.L.A. professor Marco Iacoboni. He thinks mirror neurons tie us, not just to other people's actions, but to other people's feelings.

MARCO IACOBONI (University of California, Los Angeles): So the idea was to try to figure out how the emotional system and this motor system are connected together.

We're going to go in the scanner and what you're going to do is to...

ROBERT KRULWICH: To demonstrate, he put me into this very powerful f.M.R.I. brain scanner that can peer into the brain while it's working.

And he gave me some goggles so he could show me pictures when I was in there.

MARCO IACOBONI: So you can see here the eyeball of Robert.

ROBERT KRULWICH: And once he had a good view into my brain...

MARCO IACOBONI: Nice looking brain.

ROBERT KRULWICH: Thank you.

MARCO IACOBONI: Robert, you're not supposed to talk when we scan you, all right?

ROBERT KRULWICH: Sorry.

Then he said, "Okay, I'm going to show you a bunch of faces. And for each face, I want you to imitate it."

So I did that. Then he recorded my brain while I moved my facial muscles.

MARCO IACOBONI: We're going do, right away, another one.

ROBERT KRULWICH: Okay.

Then he said "Okay, same faces, but this time, don't move a muscle, just look." So I looked.

When we checked the results...

Oh, there's my brain. I've never seen my brain before.

MARCO IACOBONI: This is your mirror area.

ROBERT KRULWICH: Iacoboni says that the part of my brain that's working when I make a face, the same part gets busy when I see the face.

Plus, when I was looking at these faces, I remember feeling extra uncomfortable, kind of bad. But when these faces came on, I felt, I don't know, I felt better, almost happy. And, in fact, at that moment I was looking at the happy face, my brain—and this is my brain at that instant—see that red area here, it shows activity in the "happy" emotional part of my brain.

And when I was imitating "happy" faces, look. I get an even bigger response.

This, says Iacoboni, is a consistent result. Mirror neurons, he believes, can send messages to the limbic, or emotional system in our brains. So it's possible these neurons help us tune in to each others' feelings. That's empathy.

MARCO IACOBONI: We strongly believe that that's a unifying mechanism that allows people to actually connect at a very simple level.

ROBERT KRULWICH: You are saying that there's a place in my brain, which...whose job it is to live in other people's minds, live in other people's bodies?

MARCO IACOBONI: That's right.

HELEN HAYES in A FAREWELL TO ARMS : Oh, darling, I'm going to die! Don't let me die!

GARY COOPER in A FAREWELL TO ARMS : Kat!

ROBERT KRULWICH: And great actors instinctively know that if they put feeling and drama into their bodies,...

HELEN HAYES in A FAREWELL TO ARMS : Hold me tight! Don't let me go!

ROBERT KRULWICH: ...their faces, we will respond.

GARY COOPER in A FAREWELL TO ARMS : You can't die. You're too brave to die!

DANIEL GLASER: What actors are experts in is using their movements to inspire feelings in the people watching. These are the experts in the mirror system.

V.S. RAMACHANDRAN (University of California, San Diego): We are intensely social creatures. We literally read other people's minds. I don't mean anything psychic like telepathy, but you can adopt another person's point of view.

LINDSAY SCHENK (University of California, San Diego): When you put it together, what do you think it's going to be?

ROBERT KRULWICH: So if mirror neurons help us connect emotionally, what about people who have trouble with this? Kids like Christian, who has autism?

LINDSAY SCHENK: Why do you like LEGO ® s?

V.S. RAMACHANDRAN: It's been known for some time that children with autism could be quite intelligent, but have a profound deficit in social interaction.

ROBERT KRULWICH: Christian can speak and read and write, but like many kids with autism, he will avoid eye contact, he often misunderstands questions.

LINDSAY SCHENK: So, Christian, can you tell me what you did in school today?

CHRISTIAN: Doing well.

LINDSAY SCHENK: You're doing well?

CHRISTIAN: Mmhmm.

ROBERT KRULWICH: Everybody wants to know what exactly causes this. So Dr. Ramachandran and his graduate student, Lindsay Schenk, designed an experiment...

LINDSAY SCHENK: So we're going be reading your brainwaves with this cap.

ROBERT KRULWICH: They recorded brainwaves while the kids opened and closed their hands and while they looked at a movie of somebody else's hands. For most people, the brainwave looks the same either way, whether they're doing or seeing. But for the kids with autism, the wave changes, suggesting, possibly, that autism might have something to do with broken mirror neurons.

V.S. RAMACHANDRAN: Their brains may indeed be different in that regard, and they may have deficits in their mirror neuron system. But we don't know this for sure yet. There needs to be...additional work needs to be done using brain imaging.

ROBERT KRULWICH: But what we do know, says Ramachandran, is that healthy human beings are intensely social. More than our cousins, the monkeys, we invent ways to connect. We invent dances, and handshakes, and games to play. We eat together. We meet and we talk. We talk a lot.

V.S. RAMACHANDRAN: Everybody's interested in this question: "What makes humans unique?" What makes us different from the great apes, for example? You can say humor—we're the laughing biped—language certainly, okay? But another thing is culture. And a lot of culture comes from imitation, watching your teachers do something.

ROBERT KRULWICH: And here V.S. Ramachandran makes a big leap. He has proposed that at a key moment in our evolution, this is his guess, our mirror neurons got better. And that made all the difference, he says, because once we humans got better at learning from each other—looking, copying, teaching—we could do things the other creatures couldn't.

V.S. RAMACHANDRAN: In other words, if you are a bear, and suddenly the environment turns cold, you need a few million years to develop polar bear type layers of fat and fur.

ROBERT KRULWICH: It would take many, many, many bear generations to select for furrier bears. But, says Ramachandran...

V.S. RAMACHANDRAN: If you're a human, you watch your father slaying another bear and putting on a fur coat, you know, skinning it, using that as a coat. You watch it, you learn it instantly. Your mirror neurons start firing away in your brain, and you've performed the same sequence, complicated sequence. Instead of going through millions of years of evolution, you've done it in one generation.

ROBERT KRULWICH: And while no one is claiming that mirror neurons are the key ingredient that makes us different from other creatures, what these neurons do suggest about us seems almost self-evident. You can see it any Sunday at a sports bar, that deep in our architecture, down in our cells, we are built to be together.

DANIEL GLASER: There'd be very little point in having a mirror system if you lived on your own. There'd be a lot of point in having a digestive system if you lived on your own. There'd be a good point in having a movement system if you lived on your own. There'd be a good point in having a visual system if you lived on your own. But there'd be no point in having a mirror system. The mirror system is probably the most basic social brain system. It's a brain system which there's no point in having if you don't want to interact or relate to other people.

ROBERT KRULWICH: But we do like to interact. And maybe now, as never before, we will understand why. Okay, now, before we leave this subject, we've designed a little mirror neuron exercise.

What we're going to do is take a wishbone, an ordinary wishbone, the kind you break for good luck, and we're going to take it—come on—and we're going to take it for a stroll. And, if your mirror neurons are working properly, when you see anything, even a wishbone walking, you know, along, you won't just watch that bone, you are going to be that bone.

The walking bone was created and designed by artist Arthur Ganson, and later in the program we will show you a host of Ganson gadgets in glorious motion.