Ep78 "Does your brain have one model of the world or thousands?"

Ep78 "Does your brain have one model of the world or thousands?"

Released Monday, 30th September 2024
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Ep78 "Does your brain have one model of the world or thousands?"

Ep78 "Does your brain have one model of the world or thousands?"

Ep78 "Does your brain have one model of the world or thousands?"

Ep78 "Does your brain have one model of the world or thousands?"

Monday, 30th September 2024
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braylar.com or call 1-877-6-BRAYLAR to learn more. What

3:07

is special about the wrinkly outer layer

3:09

of the brain, the cortex? And what

3:11

does this have to do with the

3:13

way that you come to explore and

3:16

understand the world? And by the way,

3:18

why do you see a whole image

3:20

when you open your eyes even though

3:22

each part of your visual cortex has

3:25

access to only a tiny bit of

3:27

the image? And for that

3:29

matter, the brain is divided into different areas

3:31

for sight and sound and touch and so

3:33

on. And so why when you

3:36

are petting a cat, why does the

3:38

cat seem unified? Why doesn't

3:40

the sight of the cat seem

3:42

separate from the purring and the

3:44

feel of the fur? Can

3:47

we build a new model of how the

3:49

brain works? And in what

3:51

ways is what the brain doing

3:53

something very different than what's happening

3:55

in current AI? of

6:01

our cortex. We humans have a ton

6:03

of this stuff. So take

6:06

four pieces of paper from your printer

6:09

and place them next to each other

6:11

to make one really large piece. That's

6:13

how much cortex a human has if

6:15

you were to spread out the wrinkles.

6:18

Now our nearest cousins, the great apes,

6:20

only have about one piece of paper

6:22

worth and most mammals have a lot

6:24

less than that. So something about

6:26

the story of the runaway human

6:28

success has to do with the

6:31

fact that we have way more

6:33

cortex for our body size than

6:35

any other creature. And

6:37

side note, I'm really talking about

6:40

what's called the neocortex or new

6:42

cortex because we also have a

6:44

little bit of paleocortex or old

6:46

cortex, but the thing that really

6:48

makes us outstanding is the amount

6:50

of neocortex that we have. But

6:53

what is this neocortex doing?

6:56

Well, if you look at any neuroscience

6:58

textbook, you'll see that this part of

7:01

the brain, the cortex is often drawn

7:03

with different colored regions like this red

7:05

region over here is devoted to vision

7:07

and this green one is devoted to

7:10

hearing and this yellow one to touch

7:12

and so on. But something I've been

7:14

obsessed with and write about in my

7:17

latest book, LiveWired, is that this is

7:19

the wrong way to think about it

7:21

because the neocortex is remarkably flexible. It's

7:23

not a fixed map. If

7:25

you are born blind, the part of

7:27

your cortex that we would have thought

7:30

of as visual cortex gets taken over

7:32

by hearing and touch and so on.

7:35

Now let me just be really clear what

7:37

I mean by taken over. The neurons there

7:39

are the same. The cortex

7:41

looks exactly the same from the outside,

7:43

but the function of those particular neurons

7:45

is now not visual. They

7:48

have nothing to do with visual information

7:50

anymore. Now that same neuron,

7:52

instead of firing when

7:54

it detects a moving object,

7:56

now it responds to a

7:58

touch your toe or

8:01

hearing a B flat note or

8:03

whatever. So the little

8:05

labels that we draw onto the brain,

8:08

these maps that we impose, these

8:10

are actually massively flexible. And as you

8:13

may know, I gave a talk at

8:15

Ted about this a while ago, where

8:17

I showed that you can feed in

8:19

new kinds of information, let's say through

8:21

the ears or the skin, and the

8:24

brain will figure out how to deal

8:26

with that data. It will flexibly devote

8:28

part of its cortical real estate to

8:30

that. And

8:32

this line of thinking led some scientists

8:35

like Vernon Mount Castle some decades ago

8:37

to realize that the cells of the

8:40

cortex are a one trick

8:42

pony. No neuron is

8:44

inherently a visual neuron

8:47

or a neuron devoted to hearing

8:49

or touch or smell or taste

8:51

or memory or whatever. All

8:53

parts of the cortex are perfectly

8:55

capable and willing to take on

8:57

any job. So that

9:00

suggests they're all running some sort of

9:02

basic algorithm. And it doesn't matter what

9:04

kind of data you feed in different

9:06

parts of the cortex. We'll say, cool,

9:09

I'll build a representation of that data.

9:11

I don't care if it comes from

9:13

photons or air compression waves or temperature

9:15

or whatever. I'm

9:17

on the job here to build

9:20

an understanding of whatever is coming

9:22

in locally. Now,

9:24

it's not individual neurons that are

9:26

building models, but instead groups

9:29

of many tens of thousands of

9:31

neurons arranged in a

9:33

six layered cylinder. So think about

9:35

this like you're a geologist

9:37

and you drilled out a cylinder of

9:40

rock and you saw

9:42

six layers in it, six sedimentary

9:44

layers. That's what the neocortex looks

9:46

like six layers. And it's built

9:49

out of these columns, which have

9:51

the same types of neurons with

9:53

the same connection patterns in each

9:55

column. And so think

9:57

about the cortex as being made. of

10:00

lots of these columns, like taking hundreds

10:02

of thousands of grains of rice and standing them

10:04

up on their end and packing them all next

10:07

to each other. People

10:09

have known about cortical columns for many

10:11

decades since Vernon Mount Castle first discovered

10:13

these in 1957. But

10:16

recently, someone has pulled together several

10:19

different threads to propose

10:21

how this could underlie what

10:23

the cortex is all about.

10:26

And that someone is Jeff Hawkins and

10:28

his team. And so I

10:30

met with Jeff in my studio. Now,

10:32

Jeff is one of my favorite people

10:34

because he does theoretical neuroscience. He really

10:36

tries to figure out the big picture

10:38

of what the brain is

10:41

doing. Now, Jeff has a very interesting

10:43

history. So I'll just mention that in

10:45

the 1980s, he was a graduate student

10:47

at Berkeley where he proposed a PhD

10:49

thesis on a new theory of the

10:52

cortex. But his proposal was rejected.

10:54

And so he ended up pursuing

10:57

his vision for mobile computing instead.

10:59

And in 1992, he launched the

11:01

company Palm, which made the Palm

11:04

pilot. If you remember that, this

11:06

was this little handheld device and

11:08

you could write on it with

11:10

a stylus and it would translate

11:12

your handwriting into text. And

11:14

you can use this for your address book and your

11:17

calendar and your contacts and note taking. This

11:19

was the first entrant into the world

11:21

of portable computing. It really changed the

11:23

world. Anyhow, a decade

11:26

later, Jeff returned to his original

11:28

love, which was theoretical neuroscience, trying

11:30

to figure out what's going

11:32

on with the brain. And

11:35

he wrote a book in 2004 called

11:37

on intelligence, which was very influential

11:39

on me and lots of other

11:41

thinkers I know. So I was

11:43

very excited when Jeff recently came

11:45

out with his next book that

11:47

represents his last decade and a

11:49

half of research. It's called a

11:51

thousand brains, a new theory of

11:53

intelligence, and it describes his framework

11:55

for thinking about the brain. So

11:58

without further ado, let's dive into.

12:00

a very cool new model of

12:02

the brain. Okay,

12:07

Jeff, so you are a theoretician. You think about

12:10

the brain from a high level. We're in

12:12

this era now of AI, where

12:14

AI is doing all kinds of things that

12:16

are amazing and no one expected, but you

12:18

see the brain as being very different from

12:20

what is going on with, let's say, large

12:22

language models. So tell us about that. That's

12:24

absolutely true. You know,

12:27

the current AI wave is really amazing, but

12:29

those models don't work at all like the

12:31

brain. And I think you

12:33

could start with one really fundamental difference.

12:36

Brains work through movement. We

12:39

move our bodies through the world. We move our

12:41

hands over objects to touch and learn what they

12:43

are. We move our eyes constantly. So

12:45

the inputs of the brain are constantly changing, mostly

12:47

because we're moving through the world. And

12:50

the term for that is a sensorimotor system. And

12:53

the brain can't understand its inputs unless it

12:55

knows how it's moving through the world. So

12:57

we learned by exploring, by moving

12:59

different places, picking things up, touching them,

13:01

and so on. And that's

13:03

all animals that move in the

13:06

world learn this way. So this idea that the

13:08

brain is a sensorimotor system has been known back

13:10

in the late 1800s, but

13:12

it's pretty much ignored by everybody. But

13:15

it leads to a very fundamental different

13:17

way of how we acquire knowledge and

13:19

how knowledge is represented in the brain.

13:22

Whereas today's AI most

13:25

of it's built on deep learning

13:27

or transformer technologies, which essentially we feed

13:29

it to it. It

13:31

doesn't explore it. And we feed to

13:34

large language models, we just feed it language.

13:36

So there's no inherent knowledge about what these

13:38

words mean, only what these words mean in

13:40

the context of other words. But

13:42

you and I can pick up a

13:44

cat and touch it and feel it and know

13:46

that it's warmth and we understand how its body

13:48

moves because no one has to tell us that.

13:51

We just experience it directly. So

13:54

this is a huge gap between

13:57

brains, pretty much all brains work by

13:59

sensorimotor learning. long

20:00

and around. And as you do, you build a

20:02

three-dimensional model of the cup, even though you're only

20:04

getting input from one fingertip. The

20:06

eyes are doing the same thing. It's

20:08

surprising. You don't realize this. So every

20:10

cortical column we understand now is doing

20:13

this sort of processing movement information and

20:15

sensor information, building what we call structure

20:17

or 3D models of things in the

20:19

world. So it's quite different than even

20:21

neuroscientists think about it. And

20:24

there's a lot of reasons we can talk about

20:26

how it was missed for all these years. So

20:28

in the cortex, you have essentially six layers of

20:30

cells. And a column is...

20:33

All six layers. Is all six layers. It's going

20:35

up and down. It's

20:38

like, think of it like layers of a cake. Right. Column

20:40

is you're taking a straw and

20:42

shoving it through the top. And so you've got this Good

20:44

analysis. This is the call. Okay. You

20:46

got a straw of cake. Okay,

20:48

great. And so the idea is

20:50

if you're looking at some column

20:52

in primary visual cortex,

20:55

yeah, your point, Jeff, was that it's

20:58

like looking at the world

21:00

through a straw. It only sees a little

21:02

tiny piece of the world, but because the

21:05

eyes are moving out, because you're exploring the

21:07

world, this is actually getting lots

21:09

of parts of information. It's exploring the world in

21:11

the same way that your fingertip explores the world.

21:13

Right. And it has to integrate information over time.

21:15

That's the key, right? And you can literally do

21:17

this. You can look at the world through a

21:19

straw. And you

21:21

can say, oh, what am I looking at? Well, you can't

21:23

tell until you start moving the straw. And then

21:26

you can start and you can also learn objects

21:28

that way. So literally, you can learn by looking

21:30

through a straw, which is what sort of one

21:32

column is doing. And

21:34

in your model, there are

21:37

thousands of such columns. And

21:39

each one of these is

21:41

learning a

21:43

model of the world as it's going. So tell

21:45

us about it. Right, right. So figure out what

21:47

it is and what it's doing. So

21:49

the trick of this thing is, it's a little tricky

21:51

here. You know, when you look out at the world,

21:53

you have a sense, anybody, you have

21:55

a sense where things are. I have a sense where you

21:57

are relative to me. I have a sense for this microphone.

22:00

to me, I know where my hand is, relative to this

22:02

cop. Now, it turns out

22:04

that you have any kind of sense of

22:06

location and space, you have to have neurons

22:08

representing it. There's nothing goes on

22:10

in the brain if there aren't neurons firing doing

22:12

it. It turns out most of

22:14

the machinery in the neocortex is keeping track

22:16

of where things are relative to other things.

22:19

So those six layers, all those cells, at

22:21

least half of that circuitry is

22:24

tracking where the sensory input is

22:26

coming from in the world. So if I move

22:28

my finger over this coffee cup, the

22:30

part that's getting information from my sensory, like

22:33

I'm sensing an edge, for example, as

22:35

I move my finger, it has to keep

22:37

track of where my finger is, a location

22:39

of it and its orientation relative to this

22:41

cup. It's quite complicated. But

22:44

that's what it has to do to build those models. And

22:46

now we know how it does it. There's all this evidence

22:48

for it. So the brain

22:50

is just trying to keep track of where all of

22:53

its inputs are in the world, all relative to other

22:55

things. Then it builds up these three dimensional models of

22:57

the world. So tell us about how it does that

22:59

then. Right. So you can think

23:01

about when you're in high school, you learned about Cartesian

23:03

coordinates, x, y, z coordinates, right? And

23:05

so if I wanted to say, where is something, where are

23:08

you relative to me? I might say, okay, your nose is

23:10

the origin. I could say it's some distance from here. And

23:12

so, you know, x, y, and z. Well,

23:14

you have to have something like that. But

23:17

brains don't do it that way. They do it another way. And

23:20

this was some very clever research in

23:22

the last 20 years that people discovered in

23:25

the antirhinal cortex and hippocampus, these cells

23:27

called grid cells and play cells, which

23:29

actually operate as reference frames. They are

23:32

a way of neurons to

23:34

represent locations. And

23:36

they work differently than x, y, and z. So

23:38

there's no origin. It's kind of really clever how

23:41

they work. Nature

23:43

has discovered a different way of doing this. So make

23:45

sure you tell us a little bit about that. Well,

23:47

okay. But these are well-known things.

23:49

Like grid cells, which are antirhinal cortex. What

23:51

they do is they, these cells, if you

23:53

take a set of them, individual cells are

23:56

not unique. And these real cells,

23:58

I fire at different locations in space. But if

24:00

you take a set of them, they're unique. And

24:02

so you can encode a unique location in space.

24:05

And the key thing about them is

24:07

these cells automatically update as

24:10

you move. So the original grid cells are where your

24:12

body is in a room. And

24:14

as you move, it's called path integration. It says,

24:17

OK, you're moving at this direction,

24:19

at this speed. So we'll just automatically update these

24:21

neurons as if we know where you are, right?

24:24

And so it's what sales used to do,

24:26

dead reckoning. You just say, oh, I'm heading

24:29

north for an hour or three knots there

24:31

for all these three miles in

24:33

this direction. So we know that these

24:35

cells exist. They've been well studied. People

24:37

wouldn't know about prize for these things. So

24:40

we speculated that the same

24:42

neural mechanisms, these grid cells

24:45

and equivalents, would be in the cortex in every cortical

24:47

column. And sure enough, they're

24:49

finding that now. So there's all

24:51

kinds of research now. They're finding in humans and

24:53

other animals that there are grid cell-like structures in

24:55

cortical columns. And so what does that tell you?

24:58

It tells me that that's the mechanism by which

25:00

the brain uses for reference frames. And so literally,

25:02

when you build a model of something in the

25:04

world, like a model of a cup or a

25:06

model of anything, essentially what

25:08

you're doing is you're saying, here's the sensation,

25:10

and here it's location. Here's another sensation at

25:12

a different location. Here's another sensation at a

25:14

different location. You add all these together, and

25:16

you get a three-dimensional model. You

25:18

can say, this thing consists of these features

25:20

in these locations relative to each other. And

25:24

so literally in our head, we build

25:26

models of the world that are three-dimensional

25:28

analogues of the physical things we

25:31

interact with. And that's

25:33

why you appear three-dimensional to me. You're

25:35

not an image. You're a three-dimensional structure, because I have

25:37

a three-dimensional model of humans and I have a special

25:39

model for you, David. OK,

25:43

great. India.

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