July 17, 2023 • 41 mins
How do your billions of tiny brain cells build consciousness as they chatter away with electrical spikes and chemical signals? And why is your laptop, with its sophisticated algorithms and billions of parts, presumably not conscious? Could other large systems like a city become conscious? And what does this have to do with ant hills, blue birds, or your memory of your first kiss? Join Eagleman on a journey into one of the central mysteries of neuroscience: why we have awareness.
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Speaker 1 (00:04):
How do your billions of tiny brain cells with their
electrical spikes build consciousness? And why is your laptop, with
its billions of parts and tiny electrical signals, presumably not conscious?
Could other large systems like a city be conscious? And
what does any of this have to do with ant
(00:25):
hills or bluebirds or your memory of your first kiss?
Welcome to Inner Cosmos with me David Eagleman. I'm a
neuroscientist and an author at Stanford University, and I've spent
my whole career studying the intersection between how the brain
works and how we experience life. And there's hardly a
(00:49):
better example of this intersection than consciousness. Your feeling of
being aware of your surroundings and your own existence, your
ability to experience and feel things. This somehow emerges from
the activity of our brains, and it is our experience
(01:10):
of life. So today we're going to dive deep into
a big question, possibly the central question of neurobiology. What
is consciousness. We'll talk about how we can define it,
why it's a challenge for our science to capture it,
and whether other things could be conscious. So think back
(01:32):
to your first kiss. The memory of it pops back
into your head in an instant, But where was that
image before you became conscious of it, that feeling, the
name of the person, How is it represented in your
brain before and after I ask you to think about it.
(01:53):
What's the difference between those two states? In other words,
what events in the brain constitute awareness or consciousness. I
made an earlier episode about all the things going on
in your head unconsciously without any access or awareness on
your part, and the upshot there was that at any moment,
(02:16):
there's an enormous amount of activity going on in your brain,
one hundred billion cells having little electrical spikes tens or
hundreds of times per second, and you are not consciously
aware of almost any of that activity in your brain.
But a tiny, tiny bit of that activity is conscious.
(02:39):
And so for this episode we're turning to that tiny
tiny bit and the question of what is different about
that activity than all the other activity in your brain,
and why it's such a challenge for us to figure
out how to translate that activity in your brain into
your private, colorful experience of the world. The explanation of
(03:03):
consciousness is one of the major unsolved problems of modern neuroscience,
and possibly the most important. So first, what is consciousness.
Defining it is the first step to the problem. So
there are lots of ways to try to wrap our
arms around it. But the definition that I think will
get us started the fastest is to say consciousness is
(03:26):
the thing that flickers to life when you wake up
in the morning. I mean, think about how wacky this is.
You have the same brain the moment before you wake
up in the moment after, but something just changed a
little bit about the activity, the way the signals are
moving around, and suddenly you're conscious. Whereas a moment ago
(03:47):
you were just lying there like a sack of potatoes.
You had the same brain, but you weren't aware of anything.
But now your brain cells start to run a slightly
different algorithm, and suddenly you're aware of your existence, of
your name, of your history, and your bedroom and the
smell of coffee and the feel of your sheets and
(04:10):
the details of.
Speaker 2 (04:11):
The room around you.
Speaker 1 (04:12):
Now, weirdly, what you're experiencing is a private experience. It's
what we call a subjective experience. It's not objective, which
is something we can measure and agree on a shared reality. Instead,
only you are experiencing it. So if there's someone else
in the bedroom when you wake up and that person
(04:32):
is looking around, there are different things going on in
that head, different thoughts, different feelings, a different subjective experience. Okay,
so imagine you're there and you roll over and you
look at a painting on your wall and you see
the colors. Now, what's happening inside your brain is that
(04:53):
different wavelengths of light are bouncing off the painting and
they're activating particular color photoreceptors in the back of your eyes,
which sends signals back to your brain through the optic nerve,
and in the brain, cells in the visual cortex start activating.
And if you had a magical microscope by which you
(05:16):
could view what was happening in the brain, you'd see
that you have a vast pattern of cells in the
back of the brain that activate when you look at
one painting color, and a different pattern of cells that
activate when you look at a different color. But the
question is why do you perceive the red in the
(05:36):
painting as red? There's just a particular wavelength of light
associated with your private subjective experience of seeing red.
Speaker 2 (05:45):
But the redness is something made.
Speaker 1 (05:47):
Up by the brain and could just as easily be
perceived by you as blue or green or anything else.
So why does this particular pattern of cells equally a
particular color. These are called qualia. Qualia are the features
of our experience, the internal experiences that are associated with
(06:08):
conscious states. The redness of red in this case, or
the sweetness of sugar, or the pain of a headache,
these are called qualia. Now, these are irreducible, which means
they can't be described in terms of something else. And
by the way, they're also ineffable, which means they can't
be fully explained or described in words like if I
(06:32):
ask you, what does an avocado taste like, how are
you going to answer that. Let's say that I tell
you I've never eaten an avocado, and I really want
you to tell me what that experience is. It's not
something that you can directly transmit to me, because it's
an experience that's private to you and generally cannot be
reduced to words. The last piece of the foundation that
(06:54):
we need is that when you look in the brain,
it's all just neural signals going on, and all those
signals look exactly the same. So if I opened up
a little window somewhere in the skull and showed you
just a little bit of brain tissue. And I used
that magical microscope so you can see all the spikes
zipping around.
Speaker 2 (07:13):
And I said to you, hey.
Speaker 1 (07:14):
Are we looking at the visual cortex here, or the
auditory or the somatosensory or some other part. You wouldn't
be able to tell me. I wouldn't be able to
tell you because it's all the same stuff going on
in there. It all looks the same. There aren't spikes
that equate to consciousness and other spikes that are running
around unconsciously. It's all cells and spikes, and they all
(07:37):
look alike. So why do some patterns of signals mean
the color red and others mean the smell of apple pie,
and others mean the pain of a paper cut. It's
all just signals and networks of cells. It's all the
same stuff running around. And so this is really the
heart of the mystery. The brain is made up of
(07:59):
lots of cells, eighty six billion neurons and about as
many glial cells. But they're just cells. And the brain,
as far as we can tell, is just a giant
machine that's made out of biological wetwear. It's an enormous
and quite alien computational device. But every cell in the
brain is driven by the activity of other cells, and
(08:23):
so no matter how complex the whole system is, it
appears to be fundamentally a machine in which each sequence
of actions is leading to the next sequence. It doesn't
appear that there's some extra bit in the brain that's
not just about the physical stuff. And so somehow we
need to look for consciousness in the physical stuff. And
(08:44):
we know that consciousness depends on the details in the brain,
because even very small damage to your brain can change
your consciousness. For example, if your brain is badly damaged,
you can end up in a coma without consciousness. Your
brain changes and your consciousness changes. But this happens in
(09:04):
much more subtle ways.
Speaker 2 (09:06):
Every day.
Speaker 1 (09:06):
When you ingest alcohol, the little ethanol molecules interact with
your cells and your consciousness changes. Same with drugs, same
with fatigue, same with low blood sugar. Or if you've
ever known someone who had a stroke, or got a
brain tumor, or had a traumatic brain injury, their consciousness
(09:27):
can change pretty drastically. So we know that consciousness is
intimately tied to the details of what's going on in
the brain. Now, the French philosopher Renee Descartes thought that
the physical and the mental were separate. Essentially, there's a
separate soul, and that was maybe a reasonable starting guess,
(09:48):
but centuries of neurology have taught us otherwise. When the
brain changes, your consciousness changes. You are your brain. You
can get a surgery and replace your heart entirely with
an artificial heart, and you're really no different. You can
get a kidney removed, and you're really no different. But
even a very tiny change in the brain makes a
(10:10):
giant difference to your conscious experience. Now, the amazing thing
is that modern biology knows a lot about what is
happening inside the human body, all the way down to
cells and the contents of cells, to the genome and
the molecules that make up the proteins and so on.
But where are you in that picture? Why are you
(10:33):
someone who cares about your life and listens to podcasts
and has desires and fears and aspirations and tastes and
so on. One of my mentors, the late Francis Krik,
had a chalkboard in his office and it was busy
with lots of scribbles, but there was one word right
in the center, and that was meaning. And what he
(10:55):
was reaching for with that was why in the world
does any stimulus mean mean something to us? Why do
you care about anything? How do you run a bunch
of activity through cells and get meaning? This is really
the question of consciousness, and it's a difficult problem for
neuroscience to tackle. In part, it's because the language we
(11:17):
have in science doesn't tell us how to translate from
the realm of the physical to the realm of subjective experience.
I can't write down an equation that captures the activity
in a bunch of cells and then I say, okay, look,
just do a double integral here and add something and
carry the five. And that is the feeling of rain
(11:37):
on a hot day, or the feeling of silk between
your fingertips, or the sound of a saxophone and a stairwell.
So science doesn't seem to have the language, at least
not yet, to translate from the objective to the subjective. Really,
(12:09):
the easiest way to see what's weird about consciousness is
to think about other big, complex systems that presumably don't
have consciousness. So imagine I were to hand you one
hundred billion tinker toys. You remember those old toys with
metal rods and connectors, and you can build pulleys and
levers and.
Speaker 2 (12:28):
Any kind of structure.
Speaker 1 (12:29):
Now, these tinker toys that I hand you are physical
things that can interact. So you push this one and
that pulls this and shifts that, and pulls this one
down and moves that one sideways. Each piece interacts with
the other pieces around it, just like the brain. So
the question is, can you build a tinker toy structure
that is large enough, sophisticated enough that the whole thing
(12:54):
becomes conscious? At what point do you say, Okay, I'm
going to add this one more piece and can here
and now it's enjoying the beauty of a flower, or
now it's perceiving the color indigo blue, or now it's
experiencing the smell of sunscreen on the beach. Or consider this,
(13:15):
What is the difference between your brain and your laptop.
As I said at the beginning, your brain is shuttling
signals all around, and so is your laptop. But presumably
your computer doesn't feel anything. It's just running algorithms. When
you launch a funny YouTube video, it might make you laugh,
but your computer doesn't feel amused or thrilled or surprised
(13:40):
or mirthful. It's just moving around voltages through billions of gates.
So what is the difference between you and it? Why
do electrical signals in the computer equal logical operations or
pixel colors, while electrical signals zapping around in your brain
equate to the sweetness of sugar or the sting of
(14:03):
wabi or the feeling of love. Why do we have
this internal theater instead of running like tinker toys or laptops. Now,
one thing to note is we're tackling this question is
that consciousness seems to have evolved because it is useful.
Consciousness is like a high level operating system. So back
(14:23):
in the day, you'd program computers directly with punch cards
or in machine language, But eventually we developed user interfaces
like Windows, which hid all of the complex operations of
the computer and allowed us to just deal with the
stuff we needed at the highest level. I just want
to move this thing over here, and send this email
(14:45):
and drop this picture, And that's essentially what consciousness seems
to be. It's a way for us to just have
the highest level picture of what's going on, Like let's
go get some breakfast and go for a walk. Without
needing to deal with all the billion details of how
your muscles are contracting and how you're getting oxygen to
the right places and which chemicals need to be expressed.
(15:07):
We just get the windows without all the machine code. Okay,
So let's return to the central question. How do you
build consciousness out of cells? In other words, how do
you get some magical high level property from simple low
level parts. Now that sounds impossible, but the first thing
(15:27):
to understand is the concept of an emergent property. To
understand consciousness, we may need to think not in terms
of the pieces and parts of the brain, but instead
in terms of how they all interact with each other.
So if we want to understand how simple parts can
give rise to something bigger than themselves, just think of
(15:47):
something like an ant hill, look at something like leafcutter.
Speaker 2 (15:52):
Ants.
Speaker 1 (15:53):
They've got millions of members in a colony, and they
act like farmers. They actually cultivate their own food. Different
ants have different roles. Some leave the nest to find
fresh vegetation, and when they find it, they chew off
large pieces that they carry back to the nest. But
they don't eat the leaves instead. What happens is these
(16:16):
smaller worker ants take the pieces of leaves and they
chew them into smaller pieces, and they use this as
fertilizer to grow fungus in large underground gardens. So the
ants feed the fungus, and the fungus blossoms into small
fruiting bodies which the ants later eat. So they use
(16:37):
this incredible farming strategy to build enormous nests underground that
extend sometimes hundreds of square meters. So, just like humans,
the leafcutter ants have built and perfected an agricultural civilization.
Speaker 2 (16:52):
But here's the important point.
Speaker 1 (16:53):
Although the colony is like a superorganism that accomplishes these
extraordinary feats, each ant individually behaves just like a simple
little robot. It just follows its local rules. The queen
isn't giving commands and coordinating behavior. Instead, each ant just
reacts to local chemical signals from other ants, or from
(17:18):
larvae or intruders, or food.
Speaker 2 (17:20):
Or waste or leaves.
Speaker 1 (17:22):
Each ant is just a simple autonomous unit whose reactions
depend only on its local environment and its genetically encoded rules.
So even though there's no centralized decision making, the colony
exhibits very sophisticated behavior. Each ant communicates locally with no
(17:44):
sense of the bigger picture. But what emerges at the
level of the colony is an agricultural civilization. So the
important lesson here is that the complex behavior of the
colony doesn't arise from complexity in the individuals. Each ant
doesn't know that it's part of something bigger. It's just
(18:05):
running its small, simple programs. But when enough ants come together,
a super organism emerges with collective properties that are more
sophisticated than its basic parts, and this phenomenon is known
as emergence. This is what happens when simple units interact
in the right ways and something larger emerges. The key
(18:29):
thing is the interaction between lots of ants, and this
is what's going on with the brain. A neuron is
just a type of cell. It's just like the other
cells in your body, but with some specializations that allow
it to extend processes and propagate these electrical signals. But
like an ant, an individual brain cell is just running
(18:53):
its local programs its whole life. It just carries these
electrical signals along its membrane. It spits out neuro transmitters
it gets spat on by other cells.
Speaker 2 (19:03):
That's it.
Speaker 1 (19:04):
It lives its life in darkness, embedded in other cells.
It doesn't know if it's involved in moving your eyes
to read a Tony Morrison novel, or it's involved in
moving your hands over the piano keyboard to play Mozart.
It doesn't know about you. So here's what's so weird.
Although your goals and intentions and abilities are completely dependent
(19:28):
on the existence of these little neurons, they live on
a smaller scale with no awareness of the thing they
have come together to build you. But get enough of
these basic brain cells together interacting the right way, and
the mind emerges. And I'll talk more about this notion
of emergent properties in other episodes, because the concept is
(19:51):
so fundamental. Everywhere you look you find systems with emergent properties.
Take an airplane. If you take any single hunk of
metal on the airplane, not a single one of these
pieces has the property of flight. But when you arrange
all the pieces in the right way, flight emerges. Or
(20:13):
imagine a bunch of metal poles. None has the property
of constraining the behavior of a lion, but arrange several
of these poles in the shape of a cage and
the property of lion constraining emerges. And somehow you get
a bunch of simple cells together and you wire them
up in the right way, and consciousness emerges. So the
(20:37):
pieces in parts of a system can be individually simple,
but what emerges at a higher level is all about
their interaction. So the mind seems to emerge from the
interaction of the billions of pieces and parts of the brain.
But this leads to a wacky question. Can a mind
emerge from anything with lots of inter acting parts? For example,
(21:01):
could a city be conscious? After all, a city is
built on the interactions between elements. Think of all the
signals moving through a city. You've got telephone wires and
fiber optic lines and sewers carrying waste, and every handshake
between humans, and every traffic light and so on. This
scale of interaction in a city is on par with
(21:24):
the human brain. Now, it would be very hard to
know if a city were conscious, because it doesn't have
ears and a mouth, and so how could it tell us?
How could we ask it? To answer a question like
this requires a deeper question. For a network to experience consciousness,
does it need more than just a number of parts,
(21:45):
but beyond that a very particular structure to the interactions,
and that leads us to what we have in terms
of scientific theories of consciousness. By the way, just a
side note before we get into the scientific theories. For
the purposes of this episode, we'll assume that everyone is
having the same type of conscious experience. What's interesting is
(22:06):
that we don't really have any idea how to measure consciousness,
so we don't really know if other people are conscious.
And there's a branch of philosophy called sollipsism, which suggests
that you are the only conscious person in the world
and everyone else is not conscious. They're just moving zeros
and ones around and saying the right things and acting
(22:27):
in the right way. But let's not go there. I
think it's a reasonable assumption to take on board the
notion that everyone around you is conscious and having private
internal experiences just like you are. So one way you
could go about studying consciousness scientifically is by saying, when
you are seeing the color orange, what are the neurons
(22:51):
that are lighting up? And when you're tasting cinnamon, which
neurons are popping off? Or when you're conscious of a
face or conscious of a touch or a sound, What
precisely can we measure in the brain. Now, this is
an endeavor that was emphasized by scientists like Francis Krik
and Christoph Coch. They said, hey, as the first step here,
(23:12):
let's try to find the neural correlates of consciousness, as in,
when you are conscious of something, what is lighting up
in your brain. One way you can study this is
by looking at something like binocular rivalry. So I'll explain
what that is. Let's say that your two eyes are
seeing very different images. In your left eye, I show
(23:33):
you a picture of a shoe, and in your right eye,
I show you a picture of a house, and there's
a piece of cardboard in between your eyes, so that
each eye is just seeing one thing, the shoe.
Speaker 2 (23:44):
Or the house.
Speaker 1 (23:45):
Your conscious experience is not of seeing them both at
the same time or a fusion. Instead, you see one
and then after a few seconds it switches and you
see the other. You see the shoe, and then you
see the house, and then it's back to the shoe,
and it switches every few seconds. And it's not because
you're moving your eyes around or something. It just happens
(24:08):
as your brain lands on one percept or lands on
the other. So if I ask you about your conscious experience,
you are seeing either the shoe or you're seeing the
house at any given moment. So you can use experiments
like this to then look for the correlates of consciousness.
You can map which areas of the brain are firing
when you're conscious of the shoe versus the house. We
(24:31):
can look for what is different about the patterns of
neural activity in the moments when you're perceiving the shoe
versus when you're perceiving the house. The key thing is
that I'm not changing anything in the outside world. The
only thing that's changing is your internal experiences. So the
question is what is the difference going on inside the brain. Now,
(24:51):
this sort of study has been an ongoing endeavor, but
part of the challenge with these types of experiments is
that we don't have great techniques to measure the activity
in billions of individual cells. All we have are things
like fMRI functional magnetic resonance imaging, which allows us to
measure great, big chunks of activity in the brain at
(25:14):
any moment. So we can see big blobs of activity,
but we can't narrow down with a high degree of specificity.
As technology gets better, we can see a pathway to
eventually answering these kinds of questions with greater specificity. So
(25:46):
those types of experiments are ongoing and they're fascinating, but
they're only attempting to answer the easy problem of consciousness.
What am I referring to when I say the easy problem?
Some years ago, the philosopher David Chalmers divided the scientific
exploration of consciousness into two categories. There's the easy problem
(26:09):
and the hard problem. The easy problem is to find
neural signals that correlate with consciousness, as in this region
is active when you're conscious of something. But the hard
problem of consciousness is explaining why the physical stuff of
the brain gives rise to subjective experience. It's a hard
(26:31):
problem because it's not clear how physical stuff gives rise
to a private internal life.
Speaker 2 (26:39):
That's the hard problem.
Speaker 1 (26:40):
Now we don't know the answer to this, but we
can make progress by being very clear about the different challenges.
One of them is something called the binding problem. For example,
imagine that you look at your window and you see
a beautiful blue bird fly past. Different signals from the
bird are processed by different regions of your brain. So
(27:03):
part of your brain is detecting the motion. This is
the dorsal stream. Part of your brain is recognizing the
shape of the bird. That's the ventral stream. Part of
your brain is registering the blue color. This is a
network called visual area four. Part of your brain is
listening to the sound of the bird chirping.
Speaker 2 (27:23):
This is your auditory system.
Speaker 1 (27:26):
The features of the bird are getting represented in totally
different territories of your brain. And yet somehow your brain
is able to put all of this information together so
that you see a single unified bird. You don't see
the blue bleeding off, the moving object, and the sound
(27:46):
coming from somewhere else. It all seems like one thing,
even though it's processed in a bunch of different parts. Now,
how do all these processing streams get combined. How do
our brains take the disparate pieces of information that we
receive from our senses and combine them into a single,
(28:07):
coherent experience of the world. That is the binding problem.
All these little pieces of the blue bird somehow get
bound together. What's the solution? We don't know. One theory
is that the brain uses timing information to integrate things.
This means that different pieces of information are bound together
(28:27):
by the fact that they're all popping off in the
brain at the same time. For example, when you see
the moving blue bird, the signals representing motion and the
signals representing birdness and blueness, and the signals identifying the sound,
they're all synchronized. Like imagine that you're at a stadium
full of people and you clap your hands every three seconds,
(28:50):
and scattered in the crowd are others who clap their
hands every three seconds at exactly the same time that
you do.
Speaker 2 (28:57):
The idea is that you'd come.
Speaker 1 (28:58):
To be able to pick out these folks out of
this giant crowd because you'd realize your synchrony with them.
And that's the general idea with this temporal binding theory.
And there are various other ways that people think about
how the binding problem gets solved. One is called global
workspace theory. This was proposed by my colleague Bernard Bars,
(29:21):
and the idea is you've got all these disparate elements,
but things come together in what Bars calls the global workspace,
and that's when you get consciousness. In other words, consciousness
arises from the global sharing of information within the brain.
Different brain modules are performing their specialized functions, but their
(29:42):
output is integrated and made available to the entire brain
via this hypothetical global workspace where the information gets combined
and different processes compete for attention to enter it. When
information gets into the global workspace, it becomes available to
conscious awareness and you become aware of it. So in
(30:05):
this view, consciousness emerges from the integration of all these
diverse sensory and cognitive bits into a single, unified representation,
let's say, of the bluebird. Another theory proposed by my
colleague Julio Tononi is called integrated information theory. So he's
proposed a quantitative definition of consciousness. It's not just about
(30:27):
the pieces and parts interacting. Instead, in this framework, there
has to be a particular organization that's underlying this interaction.
So to study consciousness in the laboratory, Tononi uses transcranial
magnetic stimulation TMS to compare the activity in the brain
when it's awake and when it's in deep sleep, when
(30:49):
your consciousness is not there. So by introducing a burst
of electrical current into the cortex, he and his team
can then track how the activity spreads, and what he
finds is that when his subject is awake and consciously aware,
you find these long lasting ripples moving to different cortical areas,
and this unmasks this widespread connectivity across the network. But
(31:14):
in contrast, when a person is in deep sleep, that
same pulse stimulates only a very local area and the
activity dies down quickly, So the network has lost its connectivity,
and you find the same result. When a person is
in a coma, the activity spreads very little, but as
a person emerges from a coma over weeks into consciousness,
(31:37):
the activity spreads more and more widely. So Toanoni believes
this is because when we are awake and conscious, there's
widespread communication between different cortical areas, but in contrast, when
you're asleep or in a coma, you lose this communication
across areas. So in his framework, Toinoni suggests that a
(31:58):
conscious system requires a perfect balance of enough complexity to
represent very different states. This is called differentiation. Can I
distinguish black from white, and hot from cold and so on,
and enough connectivity to have distant parts of the network
be in tight communication with each other. This is called integration.
(32:21):
So in this framework, the balance of differentiation and integration
can be quantified, and he proposes that only systems in
the right range experience consciousness. Now, if this theory turns
out to be correct, they can give a non invasive
assessment of the level of consciousness in coma patients. Now
(32:44):
it would also give us the means to tell whether
inanimate systems have consciousness. So, coming back to this question
of whether a city is conscious, this could in theory
be answered. It would depend on whether the information flow
is a ranged in just the right way with the
perfect amount of differentiation and integration. So if we can
(33:07):
come up with the right sort of network structure that's
needed to give rise to consciousness, we're on our way
to understanding whether consciousness could escape its biological origins. In
other words, although consciousness evolved along a particular path that
resulted in a brain, maybe it doesn't have to be
(33:28):
built on top of organic matter. Maybe you could build
it just as easily out of silicon, assuming the interactions
are organized in the right way. So as our understanding
of the brain continues to evolve, we may be eventually
able to answer the question of whether a city is
conscious or a set of tinker toys, or eventually AI
(33:51):
and this all comes down to the philosophical idea of materialism.
This is the notion that you can build consciousness out
of material stuff, whether that's beer cans and tennis balls,
or tinker toys or computers. The magic of conscious experience
emerges from the physical pieces and parts arranged in exactly
the right way. And if we can figure out that
(34:14):
right way, then we should be able to build it.
But I want to mention some important caveats. The main
one is that it's just a hypothesis that we can
build consciousness out of physical stuff. It always needs to
be kept in mind. Then our science is still quite young,
and there may be other things that were simply not
aware of. There's a hypothetical that I shared in my
(34:36):
book Incognito to demonstrate this idea. Imagine that somebody living
in a primitive tribe out in the desert somewhere finds
a radio in the sand, and he's never seen anything
like this, and so he picks it up and examines it,
(34:56):
and he notices there's a knob on it, and so
he sort of touched and playing with that, and he
realizes that if he turns the knob that suddenly voices
emerged from the box, and so he says, Okay, I'm
going to figure out how this box is producing the noise.
And he goes through a lot of trial and error,
and he figures out that he can take off the
back of the radio and there's these wires in there,
(35:19):
and with this nest of wires, he does experiments and
he figures out that if you pull out this wire
temporarily the voices get garbled, and if you pull out
this wire over here, the voices stop entirely, and so on.
So this person becomes a radio materialist. What he would
do is he'd conclude that if you put together this
(35:40):
nest of wires in just the right way, with the
right structure, the whole thing becomes alive and talks to you.
Speaker 2 (35:47):
But he has no idea that.
Speaker 1 (35:50):
There are radio towers that are beaming electromagnetic radiation from
distant cities. It would never strike him that any of
that is going on, because that's not part of it world.
So he would come to the erroneous conclusion that if
you put together the wires in the right way, they
generate voices. And so my point in bringing up this
(36:10):
analogy is not to say that our consciousness is getting
beamed in from somewhere else. But it is to say
it is certainly possible that we're missing big, giant pieces
of the puzzle, and that there's something that for us
would be the equivalent of not realizing that there's a
giant tower beaming signals to the radio. So I began
by pointing out that all the data we have in
(36:30):
neuroscience says that the physical integrity of the brain needs
to be there to have conscious experience, and if you
damage your brain, you change consciousness. But the radio example
is just meant to demonstrate that there still may be
lots of unknowns, And a specific example of an unknown
is this, does consciousness arise from hooking things up in
the right way or does it instead depend on some
(36:53):
special property of biological cells? In other words, is there
something special about our biology and the material that makes
up our brain that allows us to be conscious? For example,
one question that people have been asking is whether there
are quantum mechanical effects that happen in biological cells. Quantum
(37:14):
mechanics is a branch of physics. It's considered the best
scientific theory that we have because it predicts experiments out
to fourteen decimal places. But it's very counterintuitive. It's difficult
to understand because there are all kinds of very weird
effects that happen at the level of atoms. I'll go
into detail on that another episode, but for now, I'll
(37:35):
just say that some people suggest that some of the
spooky properties of quantum mechanics are just the kind of
thing we need to explain the mysteries of consciousness. Now,
other people have suggested that you can't have quantum mechanical
interactions happening in the brain because of the hot temperature,
and that may be true, but quantum effects are more
(37:56):
and more commonly being discovered in biology, so it's prematu
sure to rule it out entirely. For example, it was
discovered in recent years that photosynthesis in plants is a
quantum mechanical effect, So there are quantum mechanical effects that
happen at this temperature and this level. So I'm not
asserting there definitely are quantum effects in the human brain,
(38:17):
but that's one type of possibility that people consider for
how we might get consciousness in a human brain, but
perhaps we wouldn't in a classical computer. Just for completeness,
I'll mention one other theory that consciousness is like a
fifth force in physics. This theory is called pan psychism,
and the idea is that consciousness is a property that's
(38:39):
present in all physical matter.
Speaker 2 (38:40):
It's a property of atoms, and.
Speaker 1 (38:42):
When you get a bunch of atoms and cells together
and you collect enough of the material of consciousness, that's
when consciousness emerges. The theory suggests that the details of
the system don't really matter. It's all about getting enough
of the material of consciousness together. Now I'm not suggesting
pan psychism is true, but I'm mentioning this for completeness
(39:03):
to illustrate that our science is quite young and we
have no idea what the answer is, so we certainly
can't rule things out prematurely. Okay, So we've talked about
the mystery of consciousness and fundamentally how little we still
know about it. And there's more, which is that to
make progress towards the solution, we first need to get
straight what phenomenon we're trying to explain. Consciousness is probably
(39:27):
not like a light bulb, where it's either on or off.
It may be that consciousness varies a lot between one
person and another, between one species and another, and.
Speaker 2 (39:38):
Also within you over time.
Speaker 1 (39:42):
So consciousness is a diverse phenomenon and we still haven't
yet figured out how the physical equals the mental. The
ideas that we've looked at today start to help us
understand some of the structure that might have to be
in place for consciousness to emerge, but there are many
questions to be answered. So for the next episode, I'm
(40:02):
going to dive a little deeper into one aspect of this.
I want to ask if it would be possible to
upload our consciousness from our heads onto another substrate like silicon.
Is it possible to transfer our consciousness to someone else
or something else? And if so, could that be a
solution to the problem of mortality. To find out more
(40:29):
and to find further readings on this topic, head to
eagleman dot com slash podcast, and if you have any
questions or discussions, please send an email to podcast at
eagleman dot com. You can also watch full episodes of
Inner Cosmos on YouTube. Subscribe to inner cosmospods so you
can follow along each week with new updates until next time.
(40:51):
I'm David Eagleman, and this is Inner Cosmos.
How do your billions of tiny brain cells with their
electrical spikes build consciousness? And why is your laptop, with
its billions of parts and tiny electrical signals, presumably not conscious?
Could other large systems like a city be conscious? And
what does any of this have to do with ant
(00:25):
hills or bluebirds or your memory of your first kiss?
Welcome to Inner Cosmos with me David Eagleman. I'm a
neuroscientist and an author at Stanford University, and I've spent
my whole career studying the intersection between how the brain
works and how we experience life. And there's hardly a
(00:49):
better example of this intersection than consciousness. Your feeling of
being aware of your surroundings and your own existence, your
ability to experience and feel things. This somehow emerges from
the activity of our brains, and it is our experience
(01:10):
of life. So today we're going to dive deep into
a big question, possibly the central question of neurobiology. What
is consciousness. We'll talk about how we can define it,
why it's a challenge for our science to capture it,
and whether other things could be conscious. So think back
(01:32):
to your first kiss. The memory of it pops back
into your head in an instant, But where was that
image before you became conscious of it, that feeling, the
name of the person, How is it represented in your
brain before and after I ask you to think about it.
(01:53):
What's the difference between those two states? In other words,
what events in the brain constitute awareness or consciousness. I
made an earlier episode about all the things going on
in your head unconsciously without any access or awareness on
your part, and the upshot there was that at any moment,
(02:16):
there's an enormous amount of activity going on in your brain,
one hundred billion cells having little electrical spikes tens or
hundreds of times per second, and you are not consciously
aware of almost any of that activity in your brain.
But a tiny, tiny bit of that activity is conscious.
(02:39):
And so for this episode we're turning to that tiny
tiny bit and the question of what is different about
that activity than all the other activity in your brain,
and why it's such a challenge for us to figure
out how to translate that activity in your brain into
your private, colorful experience of the world. The explanation of
(03:03):
consciousness is one of the major unsolved problems of modern neuroscience,
and possibly the most important. So first, what is consciousness.
Defining it is the first step to the problem. So
there are lots of ways to try to wrap our
arms around it. But the definition that I think will
get us started the fastest is to say consciousness is
(03:26):
the thing that flickers to life when you wake up
in the morning. I mean, think about how wacky this is.
You have the same brain the moment before you wake
up in the moment after, but something just changed a
little bit about the activity, the way the signals are
moving around, and suddenly you're conscious. Whereas a moment ago
(03:47):
you were just lying there like a sack of potatoes.
You had the same brain, but you weren't aware of anything.
But now your brain cells start to run a slightly
different algorithm, and suddenly you're aware of your existence, of
your name, of your history, and your bedroom and the
smell of coffee and the feel of your sheets and
(04:10):
the details of.
Speaker 2 (04:11):
The room around you.
Speaker 1 (04:12):
Now, weirdly, what you're experiencing is a private experience. It's
what we call a subjective experience. It's not objective, which
is something we can measure and agree on a shared reality. Instead,
only you are experiencing it. So if there's someone else
in the bedroom when you wake up and that person
(04:32):
is looking around, there are different things going on in
that head, different thoughts, different feelings, a different subjective experience. Okay,
so imagine you're there and you roll over and you
look at a painting on your wall and you see
the colors. Now, what's happening inside your brain is that
(04:53):
different wavelengths of light are bouncing off the painting and
they're activating particular color photoreceptors in the back of your eyes,
which sends signals back to your brain through the optic nerve,
and in the brain, cells in the visual cortex start activating.
And if you had a magical microscope by which you
(05:16):
could view what was happening in the brain, you'd see
that you have a vast pattern of cells in the
back of the brain that activate when you look at
one painting color, and a different pattern of cells that
activate when you look at a different color. But the
question is why do you perceive the red in the
(05:36):
painting as red? There's just a particular wavelength of light
associated with your private subjective experience of seeing red.
Speaker 2 (05:45):
But the redness is something made.
Speaker 1 (05:47):
Up by the brain and could just as easily be
perceived by you as blue or green or anything else.
So why does this particular pattern of cells equally a
particular color. These are called qualia. Qualia are the features
of our experience, the internal experiences that are associated with
(06:08):
conscious states. The redness of red in this case, or
the sweetness of sugar, or the pain of a headache,
these are called qualia. Now, these are irreducible, which means
they can't be described in terms of something else. And
by the way, they're also ineffable, which means they can't
be fully explained or described in words like if I
(06:32):
ask you, what does an avocado taste like, how are
you going to answer that. Let's say that I tell
you I've never eaten an avocado, and I really want
you to tell me what that experience is. It's not
something that you can directly transmit to me, because it's
an experience that's private to you and generally cannot be
reduced to words. The last piece of the foundation that
(06:54):
we need is that when you look in the brain,
it's all just neural signals going on, and all those
signals look exactly the same. So if I opened up
a little window somewhere in the skull and showed you
just a little bit of brain tissue. And I used
that magical microscope so you can see all the spikes
zipping around.
Speaker 2 (07:13):
And I said to you, hey.
Speaker 1 (07:14):
Are we looking at the visual cortex here, or the
auditory or the somatosensory or some other part. You wouldn't
be able to tell me. I wouldn't be able to
tell you because it's all the same stuff going on
in there. It all looks the same. There aren't spikes
that equate to consciousness and other spikes that are running
around unconsciously. It's all cells and spikes, and they all
(07:37):
look alike. So why do some patterns of signals mean
the color red and others mean the smell of apple pie,
and others mean the pain of a paper cut. It's
all just signals and networks of cells. It's all the
same stuff running around. And so this is really the
heart of the mystery. The brain is made up of
(07:59):
lots of cells, eighty six billion neurons and about as
many glial cells. But they're just cells. And the brain,
as far as we can tell, is just a giant
machine that's made out of biological wetwear. It's an enormous
and quite alien computational device. But every cell in the
brain is driven by the activity of other cells, and
(08:23):
so no matter how complex the whole system is, it
appears to be fundamentally a machine in which each sequence
of actions is leading to the next sequence. It doesn't
appear that there's some extra bit in the brain that's
not just about the physical stuff. And so somehow we
need to look for consciousness in the physical stuff. And
(08:44):
we know that consciousness depends on the details in the brain,
because even very small damage to your brain can change
your consciousness. For example, if your brain is badly damaged,
you can end up in a coma without consciousness. Your
brain changes and your consciousness changes. But this happens in
(09:04):
much more subtle ways.
Speaker 2 (09:06):
Every day.
Speaker 1 (09:06):
When you ingest alcohol, the little ethanol molecules interact with
your cells and your consciousness changes. Same with drugs, same
with fatigue, same with low blood sugar. Or if you've
ever known someone who had a stroke, or got a
brain tumor, or had a traumatic brain injury, their consciousness
(09:27):
can change pretty drastically. So we know that consciousness is
intimately tied to the details of what's going on in
the brain. Now, the French philosopher Renee Descartes thought that
the physical and the mental were separate. Essentially, there's a
separate soul, and that was maybe a reasonable starting guess,
(09:48):
but centuries of neurology have taught us otherwise. When the
brain changes, your consciousness changes. You are your brain. You
can get a surgery and replace your heart entirely with
an artificial heart, and you're really no different. You can
get a kidney removed, and you're really no different. But
even a very tiny change in the brain makes a
(10:10):
giant difference to your conscious experience. Now, the amazing thing
is that modern biology knows a lot about what is
happening inside the human body, all the way down to
cells and the contents of cells, to the genome and
the molecules that make up the proteins and so on.
But where are you in that picture? Why are you
(10:33):
someone who cares about your life and listens to podcasts
and has desires and fears and aspirations and tastes and
so on. One of my mentors, the late Francis Krik,
had a chalkboard in his office and it was busy
with lots of scribbles, but there was one word right
in the center, and that was meaning. And what he
(10:55):
was reaching for with that was why in the world
does any stimulus mean mean something to us? Why do
you care about anything? How do you run a bunch
of activity through cells and get meaning? This is really
the question of consciousness, and it's a difficult problem for
neuroscience to tackle. In part, it's because the language we
(11:17):
have in science doesn't tell us how to translate from
the realm of the physical to the realm of subjective experience.
I can't write down an equation that captures the activity
in a bunch of cells and then I say, okay, look,
just do a double integral here and add something and
carry the five. And that is the feeling of rain
(11:37):
on a hot day, or the feeling of silk between
your fingertips, or the sound of a saxophone and a stairwell.
So science doesn't seem to have the language, at least
not yet, to translate from the objective to the subjective. Really,
(12:09):
the easiest way to see what's weird about consciousness is
to think about other big, complex systems that presumably don't
have consciousness. So imagine I were to hand you one
hundred billion tinker toys. You remember those old toys with
metal rods and connectors, and you can build pulleys and
levers and.
Speaker 2 (12:28):
Any kind of structure.
Speaker 1 (12:29):
Now, these tinker toys that I hand you are physical
things that can interact. So you push this one and
that pulls this and shifts that, and pulls this one
down and moves that one sideways. Each piece interacts with
the other pieces around it, just like the brain. So
the question is, can you build a tinker toy structure
that is large enough, sophisticated enough that the whole thing
(12:54):
becomes conscious? At what point do you say, Okay, I'm
going to add this one more piece and can here
and now it's enjoying the beauty of a flower, or
now it's perceiving the color indigo blue, or now it's
experiencing the smell of sunscreen on the beach. Or consider this,
(13:15):
What is the difference between your brain and your laptop.
As I said at the beginning, your brain is shuttling
signals all around, and so is your laptop. But presumably
your computer doesn't feel anything. It's just running algorithms. When
you launch a funny YouTube video, it might make you laugh,
but your computer doesn't feel amused or thrilled or surprised
(13:40):
or mirthful. It's just moving around voltages through billions of gates.
So what is the difference between you and it? Why
do electrical signals in the computer equal logical operations or
pixel colors, while electrical signals zapping around in your brain
equate to the sweetness of sugar or the sting of
(14:03):
wabi or the feeling of love. Why do we have
this internal theater instead of running like tinker toys or laptops. Now,
one thing to note is we're tackling this question is
that consciousness seems to have evolved because it is useful.
Consciousness is like a high level operating system. So back
(14:23):
in the day, you'd program computers directly with punch cards
or in machine language, But eventually we developed user interfaces
like Windows, which hid all of the complex operations of
the computer and allowed us to just deal with the
stuff we needed at the highest level. I just want
to move this thing over here, and send this email
(14:45):
and drop this picture, And that's essentially what consciousness seems
to be. It's a way for us to just have
the highest level picture of what's going on, Like let's
go get some breakfast and go for a walk. Without
needing to deal with all the billion details of how
your muscles are contracting and how you're getting oxygen to
the right places and which chemicals need to be expressed.
(15:07):
We just get the windows without all the machine code. Okay,
So let's return to the central question. How do you
build consciousness out of cells? In other words, how do
you get some magical high level property from simple low
level parts. Now that sounds impossible, but the first thing
(15:27):
to understand is the concept of an emergent property. To
understand consciousness, we may need to think not in terms
of the pieces and parts of the brain, but instead
in terms of how they all interact with each other.
So if we want to understand how simple parts can
give rise to something bigger than themselves, just think of
(15:47):
something like an ant hill, look at something like leafcutter.
Speaker 2 (15:52):
Ants.
Speaker 1 (15:53):
They've got millions of members in a colony, and they
act like farmers. They actually cultivate their own food. Different
ants have different roles. Some leave the nest to find
fresh vegetation, and when they find it, they chew off
large pieces that they carry back to the nest. But
they don't eat the leaves instead. What happens is these
(16:16):
smaller worker ants take the pieces of leaves and they
chew them into smaller pieces, and they use this as
fertilizer to grow fungus in large underground gardens. So the
ants feed the fungus, and the fungus blossoms into small
fruiting bodies which the ants later eat. So they use
(16:37):
this incredible farming strategy to build enormous nests underground that
extend sometimes hundreds of square meters. So, just like humans,
the leafcutter ants have built and perfected an agricultural civilization.
Speaker 2 (16:52):
But here's the important point.
Speaker 1 (16:53):
Although the colony is like a superorganism that accomplishes these
extraordinary feats, each ant individually behaves just like a simple
little robot. It just follows its local rules. The queen
isn't giving commands and coordinating behavior. Instead, each ant just
reacts to local chemical signals from other ants, or from
(17:18):
larvae or intruders, or food.
Speaker 2 (17:20):
Or waste or leaves.
Speaker 1 (17:22):
Each ant is just a simple autonomous unit whose reactions
depend only on its local environment and its genetically encoded rules.
So even though there's no centralized decision making, the colony
exhibits very sophisticated behavior. Each ant communicates locally with no
(17:44):
sense of the bigger picture. But what emerges at the
level of the colony is an agricultural civilization. So the
important lesson here is that the complex behavior of the
colony doesn't arise from complexity in the individuals. Each ant
doesn't know that it's part of something bigger. It's just
(18:05):
running its small, simple programs. But when enough ants come together,
a super organism emerges with collective properties that are more
sophisticated than its basic parts, and this phenomenon is known
as emergence. This is what happens when simple units interact
in the right ways and something larger emerges. The key
(18:29):
thing is the interaction between lots of ants, and this
is what's going on with the brain. A neuron is
just a type of cell. It's just like the other
cells in your body, but with some specializations that allow
it to extend processes and propagate these electrical signals. But
like an ant, an individual brain cell is just running
(18:53):
its local programs its whole life. It just carries these
electrical signals along its membrane. It spits out neuro transmitters
it gets spat on by other cells.
Speaker 2 (19:03):
That's it.
Speaker 1 (19:04):
It lives its life in darkness, embedded in other cells.
It doesn't know if it's involved in moving your eyes
to read a Tony Morrison novel, or it's involved in
moving your hands over the piano keyboard to play Mozart.
It doesn't know about you. So here's what's so weird.
Although your goals and intentions and abilities are completely dependent
(19:28):
on the existence of these little neurons, they live on
a smaller scale with no awareness of the thing they
have come together to build you. But get enough of
these basic brain cells together interacting the right way, and
the mind emerges. And I'll talk more about this notion
of emergent properties in other episodes, because the concept is
(19:51):
so fundamental. Everywhere you look you find systems with emergent properties.
Take an airplane. If you take any single hunk of
metal on the airplane, not a single one of these
pieces has the property of flight. But when you arrange
all the pieces in the right way, flight emerges. Or
(20:13):
imagine a bunch of metal poles. None has the property
of constraining the behavior of a lion, but arrange several
of these poles in the shape of a cage and
the property of lion constraining emerges. And somehow you get
a bunch of simple cells together and you wire them
up in the right way, and consciousness emerges. So the
(20:37):
pieces in parts of a system can be individually simple,
but what emerges at a higher level is all about
their interaction. So the mind seems to emerge from the
interaction of the billions of pieces and parts of the brain.
But this leads to a wacky question. Can a mind
emerge from anything with lots of inter acting parts? For example,
(21:01):
could a city be conscious? After all, a city is
built on the interactions between elements. Think of all the
signals moving through a city. You've got telephone wires and
fiber optic lines and sewers carrying waste, and every handshake
between humans, and every traffic light and so on. This
scale of interaction in a city is on par with
(21:24):
the human brain. Now, it would be very hard to
know if a city were conscious, because it doesn't have
ears and a mouth, and so how could it tell us?
How could we ask it? To answer a question like
this requires a deeper question. For a network to experience consciousness,
does it need more than just a number of parts,
(21:45):
but beyond that a very particular structure to the interactions,
and that leads us to what we have in terms
of scientific theories of consciousness. By the way, just a
side note before we get into the scientific theories. For
the purposes of this episode, we'll assume that everyone is
having the same type of conscious experience. What's interesting is
(22:06):
that we don't really have any idea how to measure consciousness,
so we don't really know if other people are conscious.
And there's a branch of philosophy called sollipsism, which suggests
that you are the only conscious person in the world
and everyone else is not conscious. They're just moving zeros
and ones around and saying the right things and acting
(22:27):
in the right way. But let's not go there. I
think it's a reasonable assumption to take on board the
notion that everyone around you is conscious and having private
internal experiences just like you are. So one way you
could go about studying consciousness scientifically is by saying, when
you are seeing the color orange, what are the neurons
(22:51):
that are lighting up? And when you're tasting cinnamon, which
neurons are popping off? Or when you're conscious of a
face or conscious of a touch or a sound, What
precisely can we measure in the brain. Now, this is
an endeavor that was emphasized by scientists like Francis Krik
and Christoph Coch. They said, hey, as the first step here,
(23:12):
let's try to find the neural correlates of consciousness, as in,
when you are conscious of something, what is lighting up
in your brain. One way you can study this is
by looking at something like binocular rivalry. So I'll explain
what that is. Let's say that your two eyes are
seeing very different images. In your left eye, I show
(23:33):
you a picture of a shoe, and in your right eye,
I show you a picture of a house, and there's
a piece of cardboard in between your eyes, so that
each eye is just seeing one thing, the shoe.
Speaker 2 (23:44):
Or the house.
Speaker 1 (23:45):
Your conscious experience is not of seeing them both at
the same time or a fusion. Instead, you see one
and then after a few seconds it switches and you
see the other. You see the shoe, and then you
see the house, and then it's back to the shoe,
and it switches every few seconds. And it's not because
you're moving your eyes around or something. It just happens
(24:08):
as your brain lands on one percept or lands on
the other. So if I ask you about your conscious experience,
you are seeing either the shoe or you're seeing the
house at any given moment. So you can use experiments
like this to then look for the correlates of consciousness.
You can map which areas of the brain are firing
when you're conscious of the shoe versus the house. We
(24:31):
can look for what is different about the patterns of
neural activity in the moments when you're perceiving the shoe
versus when you're perceiving the house. The key thing is
that I'm not changing anything in the outside world. The
only thing that's changing is your internal experiences. So the
question is what is the difference going on inside the brain. Now,
(24:51):
this sort of study has been an ongoing endeavor, but
part of the challenge with these types of experiments is
that we don't have great techniques to measure the activity
in billions of individual cells. All we have are things
like fMRI functional magnetic resonance imaging, which allows us to
measure great, big chunks of activity in the brain at
(25:14):
any moment. So we can see big blobs of activity,
but we can't narrow down with a high degree of specificity.
As technology gets better, we can see a pathway to
eventually answering these kinds of questions with greater specificity. So
(25:46):
those types of experiments are ongoing and they're fascinating, but
they're only attempting to answer the easy problem of consciousness.
What am I referring to when I say the easy problem?
Some years ago, the philosopher David Chalmers divided the scientific
exploration of consciousness into two categories. There's the easy problem
(26:09):
and the hard problem. The easy problem is to find
neural signals that correlate with consciousness, as in this region
is active when you're conscious of something. But the hard
problem of consciousness is explaining why the physical stuff of
the brain gives rise to subjective experience. It's a hard
(26:31):
problem because it's not clear how physical stuff gives rise
to a private internal life.
Speaker 2 (26:39):
That's the hard problem.
Speaker 1 (26:40):
Now we don't know the answer to this, but we
can make progress by being very clear about the different challenges.
One of them is something called the binding problem. For example,
imagine that you look at your window and you see
a beautiful blue bird fly past. Different signals from the
bird are processed by different regions of your brain. So
(27:03):
part of your brain is detecting the motion. This is
the dorsal stream. Part of your brain is recognizing the
shape of the bird. That's the ventral stream. Part of
your brain is registering the blue color. This is a
network called visual area four. Part of your brain is
listening to the sound of the bird chirping.
Speaker 2 (27:23):
This is your auditory system.
Speaker 1 (27:26):
The features of the bird are getting represented in totally
different territories of your brain. And yet somehow your brain
is able to put all of this information together so
that you see a single unified bird. You don't see
the blue bleeding off, the moving object, and the sound
(27:46):
coming from somewhere else. It all seems like one thing,
even though it's processed in a bunch of different parts. Now,
how do all these processing streams get combined. How do
our brains take the disparate pieces of information that we
receive from our senses and combine them into a single,
(28:07):
coherent experience of the world. That is the binding problem.
All these little pieces of the blue bird somehow get
bound together. What's the solution? We don't know. One theory
is that the brain uses timing information to integrate things.
This means that different pieces of information are bound together
(28:27):
by the fact that they're all popping off in the
brain at the same time. For example, when you see
the moving blue bird, the signals representing motion and the
signals representing birdness and blueness, and the signals identifying the sound,
they're all synchronized. Like imagine that you're at a stadium
full of people and you clap your hands every three seconds,
(28:50):
and scattered in the crowd are others who clap their
hands every three seconds at exactly the same time that
you do.
Speaker 2 (28:57):
The idea is that you'd come.
Speaker 1 (28:58):
To be able to pick out these folks out of
this giant crowd because you'd realize your synchrony with them.
And that's the general idea with this temporal binding theory.
And there are various other ways that people think about
how the binding problem gets solved. One is called global
workspace theory. This was proposed by my colleague Bernard Bars,
(29:21):
and the idea is you've got all these disparate elements,
but things come together in what Bars calls the global workspace,
and that's when you get consciousness. In other words, consciousness
arises from the global sharing of information within the brain.
Different brain modules are performing their specialized functions, but their
(29:42):
output is integrated and made available to the entire brain
via this hypothetical global workspace where the information gets combined
and different processes compete for attention to enter it. When
information gets into the global workspace, it becomes available to
conscious awareness and you become aware of it. So in
(30:05):
this view, consciousness emerges from the integration of all these
diverse sensory and cognitive bits into a single, unified representation,
let's say, of the bluebird. Another theory proposed by my
colleague Julio Tononi is called integrated information theory. So he's
proposed a quantitative definition of consciousness. It's not just about
(30:27):
the pieces and parts interacting. Instead, in this framework, there
has to be a particular organization that's underlying this interaction.
So to study consciousness in the laboratory, Tononi uses transcranial
magnetic stimulation TMS to compare the activity in the brain
when it's awake and when it's in deep sleep, when
(30:49):
your consciousness is not there. So by introducing a burst
of electrical current into the cortex, he and his team
can then track how the activity spreads, and what he
finds is that when his subject is awake and consciously aware,
you find these long lasting ripples moving to different cortical areas,
and this unmasks this widespread connectivity across the network. But
(31:14):
in contrast, when a person is in deep sleep, that
same pulse stimulates only a very local area and the
activity dies down quickly, So the network has lost its connectivity,
and you find the same result. When a person is
in a coma, the activity spreads very little, but as
a person emerges from a coma over weeks into consciousness,
(31:37):
the activity spreads more and more widely. So Toanoni believes
this is because when we are awake and conscious, there's
widespread communication between different cortical areas, but in contrast, when
you're asleep or in a coma, you lose this communication
across areas. So in his framework, Toinoni suggests that a
(31:58):
conscious system requires a perfect balance of enough complexity to
represent very different states. This is called differentiation. Can I
distinguish black from white, and hot from cold and so on,
and enough connectivity to have distant parts of the network
be in tight communication with each other. This is called integration.
(32:21):
So in this framework, the balance of differentiation and integration
can be quantified, and he proposes that only systems in
the right range experience consciousness. Now, if this theory turns
out to be correct, they can give a non invasive
assessment of the level of consciousness in coma patients. Now
(32:44):
it would also give us the means to tell whether
inanimate systems have consciousness. So, coming back to this question
of whether a city is conscious, this could in theory
be answered. It would depend on whether the information flow
is a ranged in just the right way with the
perfect amount of differentiation and integration. So if we can
(33:07):
come up with the right sort of network structure that's
needed to give rise to consciousness, we're on our way
to understanding whether consciousness could escape its biological origins. In
other words, although consciousness evolved along a particular path that
resulted in a brain, maybe it doesn't have to be
(33:28):
built on top of organic matter. Maybe you could build
it just as easily out of silicon, assuming the interactions
are organized in the right way. So as our understanding
of the brain continues to evolve, we may be eventually
able to answer the question of whether a city is
conscious or a set of tinker toys, or eventually AI
(33:51):
and this all comes down to the philosophical idea of materialism.
This is the notion that you can build consciousness out
of material stuff, whether that's beer cans and tennis balls,
or tinker toys or computers. The magic of conscious experience
emerges from the physical pieces and parts arranged in exactly
the right way. And if we can figure out that
(34:14):
right way, then we should be able to build it.
But I want to mention some important caveats. The main
one is that it's just a hypothesis that we can
build consciousness out of physical stuff. It always needs to
be kept in mind. Then our science is still quite young,
and there may be other things that were simply not
aware of. There's a hypothetical that I shared in my
(34:36):
book Incognito to demonstrate this idea. Imagine that somebody living
in a primitive tribe out in the desert somewhere finds
a radio in the sand, and he's never seen anything
like this, and so he picks it up and examines it,
(34:56):
and he notices there's a knob on it, and so
he sort of touched and playing with that, and he
realizes that if he turns the knob that suddenly voices
emerged from the box, and so he says, Okay, I'm
going to figure out how this box is producing the noise.
And he goes through a lot of trial and error,
and he figures out that he can take off the
back of the radio and there's these wires in there,
(35:19):
and with this nest of wires, he does experiments and
he figures out that if you pull out this wire
temporarily the voices get garbled, and if you pull out
this wire over here, the voices stop entirely, and so on.
So this person becomes a radio materialist. What he would
do is he'd conclude that if you put together this
(35:40):
nest of wires in just the right way, with the
right structure, the whole thing becomes alive and talks to you.
Speaker 2 (35:47):
But he has no idea that.
Speaker 1 (35:50):
There are radio towers that are beaming electromagnetic radiation from
distant cities. It would never strike him that any of
that is going on, because that's not part of it world.
So he would come to the erroneous conclusion that if
you put together the wires in the right way, they
generate voices. And so my point in bringing up this
(36:10):
analogy is not to say that our consciousness is getting
beamed in from somewhere else. But it is to say
it is certainly possible that we're missing big, giant pieces
of the puzzle, and that there's something that for us
would be the equivalent of not realizing that there's a
giant tower beaming signals to the radio. So I began
by pointing out that all the data we have in
(36:30):
neuroscience says that the physical integrity of the brain needs
to be there to have conscious experience, and if you
damage your brain, you change consciousness. But the radio example
is just meant to demonstrate that there still may be
lots of unknowns, And a specific example of an unknown
is this, does consciousness arise from hooking things up in
the right way or does it instead depend on some
(36:53):
special property of biological cells? In other words, is there
something special about our biology and the material that makes
up our brain that allows us to be conscious? For example,
one question that people have been asking is whether there
are quantum mechanical effects that happen in biological cells. Quantum
(37:14):
mechanics is a branch of physics. It's considered the best
scientific theory that we have because it predicts experiments out
to fourteen decimal places. But it's very counterintuitive. It's difficult
to understand because there are all kinds of very weird
effects that happen at the level of atoms. I'll go
into detail on that another episode, but for now, I'll
(37:35):
just say that some people suggest that some of the
spooky properties of quantum mechanics are just the kind of
thing we need to explain the mysteries of consciousness. Now,
other people have suggested that you can't have quantum mechanical
interactions happening in the brain because of the hot temperature,
and that may be true, but quantum effects are more
(37:56):
and more commonly being discovered in biology, so it's prematu
sure to rule it out entirely. For example, it was
discovered in recent years that photosynthesis in plants is a
quantum mechanical effect, So there are quantum mechanical effects that
happen at this temperature and this level. So I'm not
asserting there definitely are quantum effects in the human brain,
(38:17):
but that's one type of possibility that people consider for
how we might get consciousness in a human brain, but
perhaps we wouldn't in a classical computer. Just for completeness,
I'll mention one other theory that consciousness is like a
fifth force in physics. This theory is called pan psychism,
and the idea is that consciousness is a property that's
(38:39):
present in all physical matter.
Speaker 2 (38:40):
It's a property of atoms, and.
Speaker 1 (38:42):
When you get a bunch of atoms and cells together
and you collect enough of the material of consciousness, that's
when consciousness emerges. The theory suggests that the details of
the system don't really matter. It's all about getting enough
of the material of consciousness together. Now I'm not suggesting
pan psychism is true, but I'm mentioning this for completeness
(39:03):
to illustrate that our science is quite young and we
have no idea what the answer is, so we certainly
can't rule things out prematurely. Okay, So we've talked about
the mystery of consciousness and fundamentally how little we still
know about it. And there's more, which is that to
make progress towards the solution, we first need to get
straight what phenomenon we're trying to explain. Consciousness is probably
(39:27):
not like a light bulb, where it's either on or off.
It may be that consciousness varies a lot between one
person and another, between one species and another, and.
Speaker 2 (39:38):
Also within you over time.
Speaker 1 (39:42):
So consciousness is a diverse phenomenon and we still haven't
yet figured out how the physical equals the mental. The
ideas that we've looked at today start to help us
understand some of the structure that might have to be
in place for consciousness to emerge, but there are many
questions to be answered. So for the next episode, I'm
(40:02):
going to dive a little deeper into one aspect of this.
I want to ask if it would be possible to
upload our consciousness from our heads onto another substrate like silicon.
Is it possible to transfer our consciousness to someone else
or something else? And if so, could that be a
solution to the problem of mortality. To find out more
(40:29):
and to find further readings on this topic, head to
eagleman dot com slash podcast, and if you have any
questions or discussions, please send an email to podcast at
eagleman dot com. You can also watch full episodes of
Inner Cosmos on YouTube. Subscribe to inner cosmospods so you
can follow along each week with new updates until next time.
(40:51):
I'm David Eagleman, and this is Inner Cosmos.
Host
David Eagleman
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