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