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I'd like to talk to you today about the human brain,

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which is what we do research on at the University of California.

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Just think about this problem for a second.

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Here is a lump of flesh, about three pounds,

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which you can hold in the palm of your hand.

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But it can contemplate the vastness of interstellar space.

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It can contemplate the meaning of infinity,

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ask questions about the meaning of its own existence,

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about the nature of God.

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And this is truly the most amazing thing in the world.

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It's the greatest mystery confronting human beings:

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How does this all come about?

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Well, the brain, as you know, is made up of neurons.

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We're looking at neurons here.

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There are 100 billion neurons in the adult human brain.

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And each neuron makes something like 1,000 to 10,000 contacts

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with other neurons in the brain.

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And based on this, people have calculated

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that the number of permutations and combinations of brain activity

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exceeds the number of elementary particles in the universe.

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So, how do you go about studying the brain?

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One approach is to look at patients who had lesions

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in different part of the brain, and study changes in their behavior.

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This is what I spoke about in the last TED.

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Today I'll talk about a different approach,

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which is to put electrodes in different parts of the brain,

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and actually record the activity of individual nerve cells in the brain.

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Sort of eavesdrop on the activity of nerve cells in the brain.

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Now, one recent discovery that has been made

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by researchers in Italy, in Parma,

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by Giacomo Rizzolatti and his colleagues,

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is a group of neurons called mirror neurons,

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which are on the front of the brain in the frontal lobes.

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Now, it turns out there are neurons

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which are called ordinary motor command neurons in the front of the brain,

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which have been known for over 50 years.

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These neurons will fire when a person performs a specific action.

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For example, if I do that, and reach and grab an apple,

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a motor command neuron in the front of my brain will fire.

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If I reach out and pull an object, another neuron will fire,

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commanding me to pull that object.

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These are called motor command neurons that have been known for a long time.

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But what Rizzolatti found was

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a subset of these neurons,

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maybe about 20 percent of them, will also fire

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when I'm looking at somebody else performing the same action.

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So, here is a neuron that fires when I reach and grab something,

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but it also fires when I watch Joe reaching and grabbing something.

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And this is truly astonishing.

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Because it's as though this neuron is adopting

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the other person's point of view.

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It's almost as though it's performing a virtual reality simulation

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of the other person's action.

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Now, what is the significance of these mirror neurons?

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For one thing they must be involved in things like imitation and emulation.

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Because to imitate a complex act

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requires my brain to adopt the other person's point of view.

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So, this is important for imitation and emulation.

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Well, why is that important?

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Well, let's take a look at the next slide.

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So, how do you do imitation? Why is imitation important?

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Mirror neurons and imitation, emulation.

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Now, let's look at culture, the phenomenon of human culture.

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If you go back in time about [75,000] to 100,000 years ago,

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let's look at human evolution, it turns out

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that something very important happened around 75,000 years ago.

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And that is, there is a sudden emergence and rapid spread

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of a number of skills that are unique to human beings

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like tool use,

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the use of fire, the use of shelters, and, of course, language,

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and the ability to read somebody else's mind

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and interpret that person's behavior.

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All of that happened relatively quickly.

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Even though the human brain had achieved its present size

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almost three or four hundred thousand years ago,

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100,000 years ago all of this happened very, very quickly.

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And I claim that what happened was

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the sudden emergence of a sophisticated mirror neuron system,

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which allowed you to emulate and imitate other people's actions.

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So that when there was a sudden accidental discovery

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by one member of the group, say the use of fire,

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or a particular type of tool, instead of dying out,

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this spread rapidly, horizontally across the population,

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or was transmitted vertically, down the generations.

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So, this made evolution suddenly Lamarckian,

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instead of Darwinian.

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Darwinian evolution is slow; it takes hundreds of thousands of years.

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A polar bear, to evolve a coat,

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will take thousands of generations, maybe 100,000 years.

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A human being, a child, can just watch its parent

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kill another polar bear,

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and skin it and put the skin on its body, fur on the body,

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and learn it in one step. What the polar bear

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took 100,000 years to learn,

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it can learn in five minutes, maybe 10 minutes.

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And then once it's learned this it spreads

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in geometric proportion across a population.

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This is the basis. The imitation of complex skills

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is what we call culture and is the basis of civilization.

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Now there is another kind of mirror neuron,

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which is involved in something quite different.

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And that is, there are mirror neurons,

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just as there are mirror neurons for action, there are mirror neurons for touch.

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In other words, if somebody touches me,

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my hand, neuron in the somatosensory cortex

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in the sensory region of the brain fires.

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But the same neuron, in some cases, will fire

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when I simply watch another person being touched.

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So, it's empathizing the other person being touched.

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So, most of them will fire when I'm touched

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in different locations. Different neurons for different locations.

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But a subset of them will fire even when I watch somebody else

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being touched in the same location.

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So, here again you have neurons

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which are enrolled in empathy.

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Now, the question then arises: If I simply watch another person being touched,

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why do I not get confused and literally feel that touch sensation

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merely by watching somebody being touched?

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I mean, I empathize with that person but I don't literally feel the touch.

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Well, that's because you've got receptors in your skin,

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touch and pain receptors, going back into your brain

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and saying "Don't worry, you're not being touched.

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So, empathize, by all means, with the other person,

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but do not actually experience the touch,

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otherwise you'll get confused and muddled."

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Okay, so there is a feedback signal

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that vetoes the signal of the mirror neuron

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preventing you from consciously experiencing that touch.

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But if you remove the arm, you simply anesthetize my arm,

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so you put an injection into my arm,

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anesthetize the brachial plexus, so the arm is numb,

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and there is no sensations coming in,

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if I now watch you being touched,

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I literally feel it in my hand.

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In other words, you have dissolved the barrier

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between you and other human beings.

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So, I call them Gandhi neurons, or empathy neurons.

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(Laughter)

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And this is not in some abstract metaphorical sense.

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All that's separating you from him,

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from the other person, is your skin.

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Remove the skin, you experience that person's touch in your mind.

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You've dissolved the barrier between you and other human beings.

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And this, of course, is the basis of much of Eastern philosophy,

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and that is there is no real independent self,

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aloof from other human beings, inspecting the world,

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inspecting other people.

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You are, in fact, connected not just via Facebook and Internet,

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you're actually quite literally connected by your neurons.

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And there is whole chains of neurons around this room, talking to each other.

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And there is no real distinctiveness

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of your consciousness from somebody else's consciousness.

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And this is not mumbo-jumbo philosophy.

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It emerges from our understanding of basic neuroscience.

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So, you have a patient with a phantom limb. If the arm has been removed

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and you have a phantom, and you watch somebody else

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being touched, you feel it in your phantom.

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Now the astonishing thing is,

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if you have pain in your phantom limb, you squeeze the other person's hand,

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massage the other person's hand,

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that relieves the pain in your phantom hand,

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almost as though the neuron

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were obtaining relief from merely

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watching somebody else being massaged.

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So, here you have my last slide.

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For the longest time people have regarded science

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and humanities as being distinct.

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C.P. Snow spoke of the two cultures:

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science on the one hand, humanities on the other;

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never the twain shall meet.

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So, I'm saying the mirror neuron system underlies the interface

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allowing you to rethink about issues like consciousness,

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representation of self,

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what separates you from other human beings,

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what allows you to empathize with other human beings,

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and also even things like the emergence of culture and civilization,

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which is unique to human beings. Thank you.

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(Applause)