the age of genomics.

Your genome is the entire sequence of your DNA.

Your sequence and mine are slightly different.

That's why we look different.

I've got brown eyes;

you might have blue or gray.

But it's not just skin-deep.

The headlines tell us

that genes can give us scary diseases,

maybe even shape our personality,

or give us mental disorders.

Our genes seem to have

awesome power over our destinies.

And yet, I would like to think

that I am more than my genes.

What do you guys think?

Are you more than your genes?

(Audience: Yes.) Yes?

I think some people agree with me.

I think we should make a statement.

I think we should say it all together.

All right: "I'm more than my genes" -- all together.

Everybody: I am more than my genes.

(Cheering)

Sebastian Seung: What am I?

(Laughter)

I am my connectome.

Now, since you guys are really great,

maybe you can humor me and say this all together too.

(Laughter)

Right. All together now.

Everybody: I am my connectome.

SS: That sounded great.

You know, you guys are so great, you don't even know what a connectome is,

and you're willing to play along with me.

I could just go home now.

Well, so far only one connectome is known,

that of this tiny worm.

Its modest nervous system

consists of just 300 neurons.

And in the 1970s and '80s,

a team of scientists

mapped all 7,000 connections

between the neurons.

In this diagram, every node is a neuron,

and every line is a connection.

This is the connectome

of the worm C. elegans.

Your connectome is far more complex than this

because your brain

contains 100 billion neurons

and 10,000 times as many connections.

There's a diagram like this for your brain,

but there's no way it would fit on this slide.

Your connectome contains one million times more connections

than your genome has letters.

That's a lot of information.

What's in that information?

We don't know for sure, but there are theories.

Since the 19th century, neuroscientists have speculated

that maybe your memories --

the information that makes you, you --

maybe your memories are stored

in the connections between your brain's neurons.

And perhaps other aspects of your personal identity --

maybe your personality and your intellect --

maybe they're also encoded

in the connections between your neurons.

And so now you can see why I proposed this hypothesis:

I am my connectome.

I didn't ask you to chant it because it's true;

I just want you to remember it.

And in fact, we don't know if this hypothesis is correct,

because we have never had technologies

powerful enough to test it.

Finding that worm connectome

took over a dozen years of tedious labor.

And to find the connectomes of brains more like our own,

we need more sophisticated technologies, that are automated,

that will speed up the process of finding connectomes.

And in the next few minutes, I'll tell you about some of these technologies,

which are currently under development

in my lab and the labs of my collaborators.

Now you've probably seen pictures of neurons before.

You can recognize them instantly

by their fantastic shapes.

They extend long and delicate branches,

and in short, they look like trees.

But this is just a single neuron.

In order to find connectomes,

we have to see all the neurons at the same time.

So let's meet Bobby Kasthuri,

who works in the laboratory of Jeff Lichtman

at Harvard University.

Bobby is holding fantastically thin slices

of a mouse brain.

And we're zooming in by a factor of 100,000 times

to obtain the resolution,

so that we can see the branches of neurons all at the same time.

Except, you still may not really recognize them,

and that's because we have to work in three dimensions.

If we take many images of many slices of the brain

and stack them up,

we get a three-dimensional image.

And still, you may not see the branches.

So we start at the top,

and we color in the cross-section of one branch in red,

and we do that for the next slice

and for the next slice.

And we keep on doing that,

slice after slice.

If we continue through the entire stack,

we can reconstruct the three-dimensional shape

of a small fragment of a branch of a neuron.

And we can do that for another neuron in green.

And you can see that the green neuron touches the red neuron

at two locations,

and these are what are called synapses.

Let's zoom in on one synapse,

and keep your eyes on the interior of the green neuron.

You should see small circles --

these are called vesicles.

They contain a molecule know as a neurotransmitter.

And so when the green neuron wants to communicate,

it wants to send a message to the red neuron,

it spits out neurotransmitter.

At the synapse, the two neurons

are said to be connected

like two friends talking on the telephone.

So you see how to find a synapse.

How can we find an entire connectome?

Well, we take this three-dimensional stack of images

and treat it as a gigantic three-dimensional coloring book.

We color every neuron in, in a different color,

and then we look through all of the images,

find the synapses

and note the colors of the two neurons involved in each synapse.

If we can do that throughout all the images,

we could find a connectome.

Now, at this point,

you've learned the basics of neurons and synapses.

And so I think we're ready to tackle

one of the most important questions in neuroscience:

how are the brains of men and women different?

(Laughter)

According to this self-help book,

guys brains are like waffles;

they keep their lives compartmentalized in boxes.

Girls' brains are like spaghetti;

everything in their life is connected to everything else.

(Laughter)

You guys are laughing,

but you know, this book changed my life.

(Laughter)

But seriously, what's wrong with this?

You already know enough to tell me -- what's wrong with this statement?

It doesn't matter whether you're a guy or girl,

everyone's brains are like spaghetti.

Or maybe really, really fine capellini with branches.

Just as one strand of spaghetti

contacts many other strands on your plate,

one neuron touches many other neurons

through their entangled branches.

One neuron can be connected to so many other neurons,

because there can be synapses

at these points of contact.

By now, you might have sort of lost perspective

on how large this cube of brain tissue actually is.

And so let's do a series of comparisons to show you.

I assure you, this is very tiny. It's just six microns on a side.

So, here's how it stacks up against an entire neuron.

And you can tell that, really, only the smallest fragments of branches

are contained inside this cube.

And a neuron, well, that's smaller than brain.

And that's just a mouse brain --

it's a lot smaller than a human brain.

So when show my friends this,

sometimes they've told me,

"You know, Sebastian, you should just give up.

Neuroscience is hopeless."

Because if you look at a brain with your naked eye,

you don't really see how complex it is,

but when you use a microscope,

finally the hidden complexity is revealed.

In the 17th century,

the mathematician and philosopher, Blaise Pascal,

wrote of his dread of the infinite,

his feeling of insignificance

at contemplating the vast reaches of outer space.

And, as a scientist,

I'm not supposed to talk about my feelings --

too much information, professor.

(Laughter)

But may I?

(Laughter)

(Applause)

I feel curiosity,

and I feel wonder,

but at times I have also felt despair.

Why did I choose to study

this organ that is so awesome in its complexity

that it might well be infinite?

It's absurd.

How could we even dare to think

that we might ever understand this?

And yet, I persist in this quixotic endeavor.

And indeed, these days I harbor new hopes.

Someday,

a fleet of microscopes will capture

every neuron and every synapse

in a vast database of images.

And some day, artificially intelligent supercomputers

will analyze the images without human assistance

to summarize them in a connectome.

I do not know, but I hope that I will live to see that day,

because finding an entire human connectome

is one of the greatest technological challenges of all time.

It will take the work of generations to succeed.

At the present time, my collaborators and I,

what we're aiming for is much more modest --

just to find partial connectomes

of tiny chunks of mouse and human brain.

But even that will be enough for the first tests of this hypothesis

that I am my connectome.

For now, let me try to convince you of the plausibility of this hypothesis,

that it's actually worth taking seriously.

As you grow during childhood

and age during adulthood,

your personal identity changes slowly.

Likewise, every connectome

changes over time.

What kinds of changes happen?

Well, neurons, like trees,

can grow new branches,

and they can lose old ones.

Synapses can be created,

and they can be eliminated.

And synapses can grow larger,

and they can grow smaller.

Second question:

what causes these changes?

Well, it's true.

To some extent, they are programmed by your genes.

But that's not the whole story,

because there are signals, electrical signals,

that travel along the branches of neurons

and chemical signals

that jump across from branch to branch.

These signals are called neural activity.

And there's a lot of evidence

that neural activity

is encoding our thoughts, feelings and perceptions,

our mental experiences.

And there's a lot of evidence that neural activity

can cause your connections to change.