From the brain's point of view, What is the self? How do you put together thirty six trillion cells and have it feel like one thing? Does the self of a blind person include the tip of the walking stick? How flexible is our sense of self? And what does any of this have to do with psychedelics or trauma, or synchronized swimmers, or religious rituals or cheerleaders, or why soldiers across time and place love to march in unison in lockstep. Welcome to Inner Cosmos with me David Eagleman. I'm a neuroscientist and an author at Stanford and I've spent my career at the intersection between how the brain works and how we experience life. So I'm going to beget in today's episode with a question that I've wondered about since i was a kid. Something I've always found amazing is watching armies, thousands of soldiers march in perfect lockstep. And even as a kid, I noticed that across the world, all armies did this and this goes back to the earliest days of armies. And I know this because when I was younger, I read about how the Romans discovered a problem where if they marched in lockstep over a bridge. It would sometimes hit the resonance frequency of the bridge and then it would collapse. So they learned from their mistakes, and whenever they came to a bridge, they would purposely go out of sync with one another and they would cross the bridge that way. But the point is that they normally marched in lockstep. They, like all modern armies, loved acting as a mega organism. So why do armies love to synchronize? I mean, why not just have all the soldiers walk asynchronously however they want to, as long as they keep up well. One hypothesis would be that an army marching in lockstep is intimidating. You see something coming at you. That's like a giant, unified, single minded monster. And a related hypothesis could be that an army stepping with precision timing represents discipline and training, the way we watch dancers or synchronized swimmers, and across sports like ballet or cheerleader or whatever, athletes pursue this kind of perfect synchronization. In other words, the army does it not just because it's scary, but also because it represents discipline and training to get there. And these both seem like reasonable hypotheses. But I have something else to segest today, something that I think you might find quite surprising and hopefully enlightening because of all the other things that it sheds light on. So what seems like an arbitrary question can sometimes unearth a lot. But first, let's start at the beginning. So let's step back to sixteen thirty seven, when Renee de Kartes famously wrote Japan's don't suis I think? Therefore I am? Now when he says I, we all understand what he means here, we think, but what exactly is the I If you think it's obvious what the self is, get ready for some eye openers, because we're going to see how the self emerges from computations in the brain and how it can morph in unexpected ways. So let's start by noting that nothing seems more obvious than you feel like a single entity. But that's strange because you're actually built out of thirty six trillion individual cells communicating through chemical and electrical signals. But you don't feel like that. You don't feel like a swirling bath of seven billion, billion billion atoms, not to mention that you're constantly shedding atoms and gaining new ones, such that your body is composed of entirely new atoms about every seven years. Despite all this, you feel like one stable thing. You feel like you. You have a name, You have a history and a memory, and a personality. You have desires, and you are unique personality. You have a self, and that self seems to be located right behind your eyeballs. Now this is wild, right, because consider other scenarios in which there are lots of pieces and parts working together. Let's say I go out to some big field and I set up a bunch of and pulleys and levers, and I start hooking everything up and this turns that, and that affects that, and this lever pulls that thing, and I start adding more and more parts in this big crazy machine gets larger and larger. Here's the question, At what point do I add one more lever and I say, ah, Now this is no longer a Frankensteinian collection of trillions of individual pieces, but suddenly it has the experience of a living unity. Or just take your computer. It's made of billions of transistors and resistors and capacitors. It's sending zeros and ones all around. But the question is does your MacBook pro have a sense of itself? Do you think it ever aspires to be something greater in its life? Or does it feel a sense of embarrassment and its performance sometimes, or does it ever desire to be loved by another computer? Now, the reason your sense of self is so mysterious is because your brain is just made up of pieces and parts cells with straightforward properties, each cell by itself as just doing basic sell things. So why does this giant collection, when hooked up and interacting in the right way, have a unified sense of a single you interacting with the world through time. You have this conscious perception of yourself as a thing such that the thirty six trillion cells that comprise you can collaborate to go to a dance club tonight, or meet friends at the coffee shop, or go to a bookstore, or take a road trip across the nation, acting like a single thing. So why do you feel like a unified entity? Now? The answer, presumably is an evolutionary one. Those cells are all hanging together, and this collection has to take the whole vast complet space of possibilities and crunch it down to a single decision. For example, your body can go to the left or go to the right to get around the tree, but you can't do both, and that's why you have to squeeze down all the chattering of billions of neurons to a single choice and control your trillions of cells to do something that makes sense in the outside world. I've mentioned before that the brain is typically celebrated for its parallel processing, but in fact, just as importantly it should be celebrated for its serialization. In other words, its ability to conclude something, to decide something from the vast space of possibilities, to take all the rumbling trillions of cells and get to a single conclusion about what to do next. So that's presumably why you have a unified sense. But the story gets stranger from here because the sense of self is not fixed, it's not nailed into place. Instead, it's quite fluid, and in many scenarios what we find is a dissolution of the self. For example, various drugs can have profound effects on an individual's sense of self. They lead to an alteration of one's identity. And this is amazing, right, because these are invisibly small molecules with particular shapes, and when they enter your system and bind to particular receptors in your brain and change the activity just a little bit, then this neural technology that builds selfness breaks down. For example, a lot of psychedelic drugs do this. They bind to particular receptors here and there, and they cause profound alterations in the feeling of self. Think of LSD or SILAS or DMT. What happens when people take this is they report a dissolving of their ego boundaries, leading to experiences of what's sometimes called an ego death, meaning the loss of self identity. You also have substances like ketamine or PCP or some synthetic cannabinoids, and these can trigger feelings of depersonalization and dissociation. In other words, people on these drugs get a sense of detachment from their own body, or their emotions or their surroundings, so they have a distorted perception of self. And you sometimes see this with certain psychiatric medications when they're misused or taken in appropriately. They can alter cognition and emotion and often lead to a feeling of disconnection from a person's identity or sense of self, and all throughout the drug world, you find people mixing different drugs together and getting all kinds of severe things like dissociation and confusion and a loss of coherent self awareness. So what does this tell us? In all these situations, we see how invisibly small molecules can disrupt the normal, very delicate functioning of the brain, and that busts up the computation of the self. And you can find the same thing not just from the influence of molecules, but also from the influence of experiences. Just look at something like post traumatic stress disorder. Beyond the emotional challenges that we find there, we also find cognitive impacts like a pervasive sense of disconnection from one's identity and a loss of coherence in self perception. For example, sometimes people report feeling like an object rather than a person. Now, what happens when we measure the effects of post traumatic stress disorder in the brain. While there's a network called the default mode network, and this network is critical for constructing one sense of self, and in post traumatic stress disorder, for example, you can find in neuroimaging that the connectivity gets disrupted, and this appears to correlate with problems with one's perceived sense of self. This feeling that people sometimes have in post traumatic stress disorder, where they say they don't know who they are, where they feel like they've stopped existing. What this reflects is a disruption in their networks that are critical to computing the self, and we see disruptions of the self in closely related clinical settings also, for example, in dissociative identity disorder. This is where people usually who have been through some trauma, will have a fragment of their self into different identities. They switch personalities. They can have these sudden changes in mood and in their behavior, and family members can usually tell when a person switches their personality. And by the way, they often get amnesia. They can't remember what they said just a few minutes ago when they were speaking as one of their other personalities. I'll just note that often people with dissociative identity disorder are misdiagnosed as having schizophrenia because their beliefs are interpreted as a delusion. But I think more properly this could be interpreted as yet another demonstration that the brain has to go through an enormous amount of very delicate work to construct the self, and there are lots of ways this can be disrupted. Now, how can we study this? In the lab, one of my colleagues at Stanford, Joseph Parvizi, was studying patients with epilep see people who have electrical seizures in the brain. So one day one of his patients with APLEPSI tells him every time I have a seizure, I have a sense of depersonalization and dissociation. Everything's unreal, It's like it's not happening to me. And Parvez finds out that this patient's seizures started in a tiny brain area right in the brain's midline, called the anterior precuneus. And there was something very interesting about this area because it's not part of the default mode network, which I mentioned a moment ago, but instead it's a node at the center of a different network consisting of different areas. And this network integrates data about where you are and how you're moving, and where your muscles and joints are, so it's involved in building a mental map of your physical self. Now, just before I tell you more about this, one of the things I think is interesting is how parvs this ditinguishes between the I and the me. He says, Look, for every action we take, even during dreams, there's always an agent behind it. We call that agent I. But me is everything we have stored in our memories about the I. In other words, the eye has to do with your sense of your body in the immediate here and now, with a particular point of view, a first person perspective that belongs to only you. But the me, that's the narrative self, that has to do with actively or passively thinking about your past life or planning your future, things like memory and habits and personality, emotions, feelings for others, what lies ahead, and so on. Okay, now here's the key point from the brain's point of view. These two functions of the eye and the me, they're actually underpinned by separate networks of brain areas. These networks interact, they're not the same. So the me involving my memory, inhabits and personality and emotions, that mostly involves the default mode network. But the eye, which gives my sense of my particular point of view right now, that involves this other network where the anterior precunius sits at the center. And what Parvizi found is when that network becomes disrupted, let's say by an epileptic seizure that disrupts your self in the here and now. So he stuck electrodes into the anterior precuneus and zaps with electricity, and people say that something weird happens to their sense of physical self. They get a depersonalization, similar to what happens with psychedelics. It's not an out of body experience. People still feel like they're in their bodies, but they generally feel like there's a change in their orientation or their location, depending on where the stimulation happens. They feel like they're floating, your sinking, and it doesn't make any sense when they look around and they see where they are. And so their report was that the world around them seemed unreal. So again I want to be clear that you require this extraordinarily specific, delicate operation of multiple networks in the brain to make you feel a particular way, to give you an eye that's anchored in space with a point of view, and a me with a stable sense of who you are, and a connection to your memories and your sense as an individual. Now, assuming you have average good luck, then you'll never even be conscious of this perspective on the world. But if your brain gets disrupted from drugs or trauma or epilepsy, you're suddenly going to see it. Your world will seem unreal, and you'll come to understand that the self is a construction of the brain and needs all the pieces and parts to be running just right. Okay, so what we've talked about so far is the way the self can get disrupted. But now I want to switch gears to a less studied area. Instead of the dissolution of the self, I want to consider the expansion of the self. Now. I started thinking about this many years ago, even when I was a kid. I noticed that when you ride a bicycle, and maybe you accidentally, without meaning to, you run over a little worm that's crawled onto the sidewalk, and you recoil as though you'd physically stepped on the worm yourself with your bare feet, even though it was only the bicycle that touched the worm. So I started wondering if the bicycle becomes essentially a part of you, an extension of the self of some sort. And then when I got to college, I ended up reading some philosophers like Maurice Merleau Ponti and Gregory Bateson who posed a question like this about a blind man with a stick. The question was where does the blind man's self end and the rest of the world begin. You can think of the stick as like an extended cognitive system that pulls in information from the world. So does the blind man end at the handle of the stick or at the tip of the stick? Or does his self end somewhere in between? As Merleau Ponti wrote, quote, the blind man's cane has ceased to be an object for him. It's no longer perceived for itself. Rather, the caine's furthest point is transformed into a sensitive zone end quote. In other words, since the world is a deserved through the stick, it becomes part of the man's self. So humans alter the borders of their self all the time by using new instruments. I talked way back in episode two about dogs who learn how to ride skateboards, and even though wheels are not a part of the evolutionary history of canines, it becomes part of the dog. They become one with the skateboard, and I talked about surfing dogs even though the dog skeleton didn't evolve to be big and long and flat. The dog has no trouble incorporating the surfboard into its body plan into itsself. So we're not limited by the borders of our skin, but instead these self can expand. And I've also previously mentioned some experiments that were done years ago where a monkey learns to use a little rake to get some food that he couldn't otherwise reach. And once the monkey becomes proficient at this, there are cells in its brains sells that command actions and sells that sense what's going on. These cells change to include the rake in the space that they care about, what's known as their receptive field. In other words, the rake literally becomes part of the monkey. So whether we're talking about bicycle tires or walking canes for the blind, or the monkey and the rake, we see that the notion of the self has flexibility. It's not something that's just genetically pre programmed and fixed into place. So how does the body decide what to include what makes up the self? Well, in my last book, Live Wired, I proposed an answer to this. In part, it's about control. If the brain can control something, it becomes part of the self. So, for example, when my brain sends out signals to move my arm. My arm follows the commands, and therefore it becomes part of my self. The monkey's rake becomes part of what it can use and command in the world, so it becomes in a sense, part of its body. Now. Fundamentally, remember the brain is locked in silence and darkness, and so what does command mean to it? Fundamentally, it's all about prediction. Now. In an earlier episode forty four, we dove into the issue about the brain being a prediction machine. That's all it's trying to do. Locked in silence and darkness, It's trying to figure out what's happening in the world out there, And for really sophisticated brains like ours, it's not just about reacting to what happened, but instead having a model of the world that makes predictions about what will happen. So given this, what else can become a part of the cell. We are used to our brains controlling just our limbs, and this is because evolution has built us with muscle and tendons and nerves. But evolution never came up with controlling distant limbs via bluetooth. So in theory, if you could control a robotic arm with your brain, or a metal avatar that's all the way across town. This would become part of your self. And one question is what consequence would this have for your conscious experience. The answer is that the robot or the avatar would be perceived as a part of you. It would be another limb. It would be an unusual limb because of the physical gap between you and it, but it would nonetheless qualify as an extension of you. Think of the Avatar movies. The protagonist Jake Sully thinks of something he wants to do with his limited body, and the eight foot all avatar moves accordingly, and therefore the avatar becomes an extension of his self. By the way, you see this all the time. In the military. A soldier is in charge of driving a bomb sniffing robot, and everything the soldier commands with his joystick, the robot does. And at some point, if the robot gets blown up, it's not unusual to see one of these soldiers crying and heartbroken. It's like a part of them physically has been lost. Now, if this kind of extension of the self seems strange, just remember that you have everyday experience with this. Whenever you look in a mirror and move your body around, you see a distant object move in perfect synchrony with your motor commands. Your brain says, lift your arm, and you see this thing across the room, lift its arm. It's a perfect prediction. And so when you do that, you understand the reflection as your self. You don't feel any direct sensation from the distant limbs, but your brain registers the prediction. Every time I send out a command for X, that body over there does X, and that's enough for your reflection to become a member of the selfhood tribe. And one of the things I've written about recently is expanding oneself using virtual reality. You're in a virtual world and you raise your arm and you see your virtual avatar and the virtual mirror raise its arm. You tilt your head and it tilts its head. Now, interestingly, people are studying this in the context of empathy, because you can put someone else's face on the virtual avatar. Let's say someone of a different gender and a different race, and the question is how do you feel after having them be a part of you for a while. And you can experiment with very different kinds of bodies in VR. What if in a VR world you're one hundred feet tall, or you have eight legs or three arms. In all of these cases, you can learn to control that body, to predict what's happening, and then that body becomes you. The identity of the self is surprisingly flexible. So what I've proposed is that what the body can control becomes the self. And this all pivots on predictability, and so one tragic lesson we can glean from this is what happens when a person gets damage to their peripheral nerves so they can no longer control their limb. And what happens is they can get a disorder called asomatic nosea, which means they now deny ownership of the limb that they can't control. So as somatic nosia means not knowing one's body. And in the clinics you'll find the strangest things where somebody will say this leg does not belong to me, and sometimes they'll insist that the limb belongs to somebody else. They'll attribute the leg to, say a dead friend or a relative, or a phantasm or a devil, or one of the doctors taking care of them. They'll say the leg was sewn onto her, but it's not hers. She'll explain that her own real limb was stolen or is simply missing. And in variance of this disorder, people will sometimes construe the limb as an animal, perhaps like a snake, with its own independent life force and intentions. But the point is it's no longer a part of their self. So I was surprised when I found there was no gold standard explanation for this in the literature. But you'll have no trouble guessing my proposal, which is that the brain can no longer control the limb, and so the limb falls from the brotherhood of the self. By the way, sometimes these patients have a small window of lucidity in which they re recognize their limb as their own, but it doesn't last long. I hypothesize that this might result when the leg happens to move the way that they had intended accidental predictability. That might be a feeling of wanting to move the foot to the left, and then the foot happens to move that way, which leads the owner to take credit for the action. And given a person's lifelong experience of controlling her leg It should come as no surprise that even a temporary impression of control can snap it back into alignment with the self, even if just for a moment. So what you can predict becomes part of the self. Now. One of the places this becomes really interesting is with relationships, because when you come to know someone well, you in a sense expand yourself. They become a part of you. Again. This is because the brain is a prediction machine. You've spent a lot of time with the people in your life, and so you have rich predictions about them. You have increasingly sophisticated guesses about what they're going to do in some situation, and in this sense they become a part of you. Now, your predictions about other people are never going to be perfect, and those people will often surprise you. And so the degree to which your spouse or friend, your family member remains unpredictable is the degree to which she or he remains different from the self, remains independent from you. Nonetheless, they are, to a greater or lesser degree, a part of your brain's notion of the self, because you have some degree of prediction about them, and as a result, you can be proud of their accomplishments and feel happy when they're happy, and sad when they're sad. And part of what's hard about a breakup or the death of a loved one is it something like a self contraction. Okay, so now we're set up to return to the question that I posed at the beginning of the episode. Why do soldiers march in lockstep? And I think you can now guess my hypothesis. It's not just about intimidation, it's not just about discipline. It's about giving each soldier the usion of a larger self. If you are an individual soldier, you experience this expansion of the self, this enlargement because there are all these other bodies moving in a way that is precisely predictable by your brain. Your brain sends out motor commands that say, okay, stomp my right leg exactly now. And after that command goes out from the brain and down the spinal cord, it witnesses the power of a thousand legs, all stomping at the same moment. Your brain has sent out a command, and you feel the earthshake as a result. It's empowering to be part of a group because your self now consists of thousands of bodies. There are a dozen ways to look at this issue of marching in lockstep socially, but from the neuroscience point of view, when you do stuff in synchrony with others, there's an expansion of the brain's construction of this self. So this is my hypothesis for why we see so much synchronization around us. You see this in Japanese festivals where everyone is doing the same thing at the same time. Or take the Hodge, which is this annual Islamic pilgrimage to Mecca. You've got pilgrims from all over the world travel to Mecca to flow around this big cube at the center of the Grand Mosque. Is very stunning to see hundreds of thousands of bodies swirling like a larger mega organism. And this is typical of religious ritual. If you only knew neuroscience and knew nothing about societal behavior, you might predict the existence of this sort of thing because the commands from each pilgrim's brain is multiplied by the feedback from hundreds of thousands of other pilgrims, and that kind of feedback is intoxicating to human brains. And as I said, you find this sort of synchronization in all religious rituals. Everyone is doing the same thing at the same time, ideally in the same costume. And I propose that it's not accidental everyone stands and sits at the same time, or genuflex or chants. When you look across religions, I suspect that the details of the rituals don't matter much at all. Instead, it's the allure of learning how to fuse your identity with a larger group. You think, wow, I can learn the steps, the moves, the words here and be part of a larger self. That is the promise that is being offered to you. You never find religious rituals where everything is desynchronized, where the promise is come into my religion, where we each do our own thing. You walk in whenever you want, you face wherever you want, Everyone sing and chant out of tune. You just don't see religions where there's no bigger voice, no bigger self acting in unison. And of course you find exactly the same synchronization in non religious ceremonies. One hypothesis about the origin of music and dancing is that this came from early primates who would synchronize with one another, and when we dance, we see this. If you're an observer of human behavior, it's hard to ignore that humans love to be synchronized on the dance floor. And you can imagine a bunch of early primates sitting around and all banging rocks together, making shouts or chants that aren't random but synchronized. You can see how the drive for a larger self could be at the root of this. And when you start looking for humans synchronizing, you see it everywhere. You see it in group exercise classes like yoga or dance or aerobics. Everyone's doing the same thing at the same time, and that synchronization fosters this sense of unity. You get the same thing in choirs where everyone sings together, or at music concerts, where the crowds synchronize their movements to the rhythm of the music. They sway, they clap, they sing along together. At sports events, you have fans synchronize their chance just like a protest marches. What's happening if you're at the event is that your brain sends commands to your larynx with the prediction that it will hear your voice in return. But now you hear your voice times a thousand, and you feel like your self is larger and more powerful. So let's wrap this up. My interest is in this question of where does your self end and others begin? And although you think you end at the borders of your skin, you're actually a flexible creature, extending past what you can see and feel, incorporating it tooferent times, your family, your partners, your teams, the culture in which you're embedded. And I think looking at this from the neuroscience point of view is a very powerful way to understand rituals and dancing inquires and religious ceremonies. Even on the political scale. It might shed light on our study of in groups and outgroups, and our understanding of things like patriotism. And this all fundamentally comes down to an extension of this self, which always reminds me to question, what would happen if you were born in a different culture, a different neighborhood, a different era in time. Would you be you? Presumably not in a way that we would recognize. You are wired up by the world that you happen to be in. All of it, to a lesser or greater degree, becomes part of what your brain considers your self. So I'm fascinated with this question of how we draw the limits of our selves. For example, I'm thinking some thoughts, and I jot notes throughout the week, and I go into my studio and record this podcast, and you listen to it. But it might be a week later after I've recorded it, or maybe you are listening to this long after I'm dead, and yet we're still communicating. I'm taking ideas from my head and capturing them in zeros and ones stored on a server somewhere, and eventually that gets transmitted over the Internet or maybe in a century, over Internet twelve to your device, and then my words reach you, and you're suddenly connected with me. I'm right next to you, I'm in your ear, I'm in your brain. My words make physical changes to the networks inside your head. And if we're alive at the same time, you can send me an email and I read the words on the screen that you wrote, and we are connected. And with our current communication technologies, this is more true than ever that our brains have the opportunity to expand the self, from literature to television, to podcasts to the Internet. We increasingly have the opportunity to become larger than we would otherwise be. Please visit eagleman dot com slash podcast for more information and to find further reading. Send me an email at podcast at eagleman dot com with questions or discussion, and check out and subscribe to Inner Cosmos on YouTube for videos of each episode and to leave comments. Until next time, I'm David Eagleman and this is Inner Cosmos

From the brain's point of view, What is the self? How do you put together thirty six trillion cells and have it feel like one thing? Does the self of a blind person include the tip of the walking stick? How flexible is our sense of self? And what does any of this have to do with psychedelics or trauma, or synchronized swimmers, or religious rituals or cheerleaders, or why soldiers across time and place love to march in unison in lockstep. Welcome to Inner Cosmos with me David Eagleman. I'm a neuroscientist and an author at Stanford and I've spent my career at the intersection between how the brain works and how we experience life. So I'm going to beget in today's episode with a question that I've wondered about since i was a kid. Something I've always found amazing is watching armies, thousands of soldiers march in perfect lockstep. And even as a kid, I noticed that across the world, all armies did this and this goes back to the earliest days of armies. And I know this because when I was younger, I read about how the Romans discovered a problem where if they marched in lockstep over a bridge. It would sometimes hit the resonance frequency of the bridge and then it would collapse. So they learned from their mistakes, and whenever they came to a bridge, they would purposely go out of sync with one another and they would cross the bridge that way. But the point is that they normally marched in lockstep. They, like all modern armies, loved acting as a mega organism. So why do armies love to synchronize? I mean, why not just have all the soldiers walk asynchronously however they want to, as long as they keep up well. One hypothesis would be that an army marching in lockstep is intimidating. You see something coming at you. That's like a giant, unified, single minded monster. And a related hypothesis could be that an army stepping with precision timing represents discipline and training, the way we watch dancers or synchronized swimmers, and across sports like ballet or cheerleader or whatever, athletes pursue this kind of perfect synchronization. In other words, the army does it not just because it's scary, but also because it represents discipline and training to get there. And these both seem like reasonable hypotheses. But I have something else to segest today, something that I think you might find quite surprising and hopefully enlightening because of all the other things that it sheds light on. So what seems like an arbitrary question can sometimes unearth a lot. But first, let's start at the beginning. So let's step back to sixteen thirty seven, when Renee de Kartes famously wrote Japan's don't suis I think? Therefore I am? Now when he says I, we all understand what he means here, we think, but what exactly is the I If you think it's obvious what the self is, get ready for some eye openers, because we're going to see how the self emerges from computations in the brain and how it can morph in unexpected ways. So let's start by noting that nothing seems more obvious than you feel like a single entity. But that's strange because you're actually built out of thirty six trillion individual cells communicating through chemical and electrical signals. But you don't feel like that. You don't feel like a swirling bath of seven billion, billion billion atoms, not to mention that you're constantly shedding atoms and gaining new ones, such that your body is composed of entirely new atoms about every seven years. Despite all this, you feel like one stable thing. You feel like you. You have a name, You have a history and a memory, and a personality. You have desires, and you are unique personality. You have a self, and that self seems to be located right behind your eyeballs. Now this is wild, right, because consider other scenarios in which there are lots of pieces and parts working together. Let's say I go out to some big field and I set up a bunch of and pulleys and levers, and I start hooking everything up and this turns that, and that affects that, and this lever pulls that thing, and I start adding more and more parts in this big crazy machine gets larger and larger. Here's the question, At what point do I add one more lever and I say, ah, Now this is no longer a Frankensteinian collection of trillions of individual pieces, but suddenly it has the experience of a living unity. Or just take your computer. It's made of billions of transistors and resistors and capacitors. It's sending zeros and ones all around. But the question is does your MacBook pro have a sense of itself? Do you think it ever aspires to be something greater in its life? Or does it feel a sense of embarrassment and its performance sometimes, or does it ever desire to be loved by another computer? Now, the reason your sense of self is so mysterious is because your brain is just made up of pieces and parts cells with straightforward properties, each cell by itself as just doing basic sell things. So why does this giant collection, when hooked up and interacting in the right way, have a unified sense of a single you interacting with the world through time. You have this conscious perception of yourself as a thing such that the thirty six trillion cells that comprise you can collaborate to go to a dance club tonight, or meet friends at the coffee shop, or go to a bookstore, or take a road trip across the nation, acting like a single thing. So why do you feel like a unified entity? Now? The answer, presumably is an evolutionary one. Those cells are all hanging together, and this collection has to take the whole vast complet space of possibilities and crunch it down to a single decision. For example, your body can go to the left or go to the right to get around the tree, but you can't do both, and that's why you have to squeeze down all the chattering of billions of neurons to a single choice and control your trillions of cells to do something that makes sense in the outside world. I've mentioned before that the brain is typically celebrated for its parallel processing, but in fact, just as importantly it should be celebrated for its serialization. In other words, its ability to conclude something, to decide something from the vast space of possibilities, to take all the rumbling trillions of cells and get to a single conclusion about what to do next. So that's presumably why you have a unified sense. But the story gets stranger from here because the sense of self is not fixed, it's not nailed into place. Instead, it's quite fluid, and in many scenarios what we find is a dissolution of the self. For example, various drugs can have profound effects on an individual's sense of self. They lead to an alteration of one's identity. And this is amazing, right, because these are invisibly small molecules with particular shapes, and when they enter your system and bind to particular receptors in your brain and change the activity just a little bit, then this neural technology that builds selfness breaks down. For example, a lot of psychedelic drugs do this. They bind to particular receptors here and there, and they cause profound alterations in the feeling of self. Think of LSD or SILAS or DMT. What happens when people take this is they report a dissolving of their ego boundaries, leading to experiences of what's sometimes called an ego death, meaning the loss of self identity. You also have substances like ketamine or PCP or some synthetic cannabinoids, and these can trigger feelings of depersonalization and dissociation. In other words, people on these drugs get a sense of detachment from their own body, or their emotions or their surroundings, so they have a distorted perception of self. And you sometimes see this with certain psychiatric medications when they're misused or taken in appropriately. They can alter cognition and emotion and often lead to a feeling of disconnection from a person's identity or sense of self, and all throughout the drug world, you find people mixing different drugs together and getting all kinds of severe things like dissociation and confusion and a loss of coherent self awareness. So what does this tell us? In all these situations, we see how invisibly small molecules can disrupt the normal, very delicate functioning of the brain, and that busts up the computation of the self. And you can find the same thing not just from the influence of molecules, but also from the influence of experiences. Just look at something like post traumatic stress disorder. Beyond the emotional challenges that we find there, we also find cognitive impacts like a pervasive sense of disconnection from one's identity and a loss of coherence in self perception. For example, sometimes people report feeling like an object rather than a person. Now, what happens when we measure the effects of post traumatic stress disorder in the brain. While there's a network called the default mode network, and this network is critical for constructing one sense of self, and in post traumatic stress disorder, for example, you can find in neuroimaging that the connectivity gets disrupted, and this appears to correlate with problems with one's perceived sense of self. This feeling that people sometimes have in post traumatic stress disorder, where they say they don't know who they are, where they feel like they've stopped existing. What this reflects is a disruption in their networks that are critical to computing the self, and we see disruptions of the self in closely related clinical settings also, for example, in dissociative identity disorder. This is where people usually who have been through some trauma, will have a fragment of their self into different identities. They switch personalities. They can have these sudden changes in mood and in their behavior, and family members can usually tell when a person switches their personality. And by the way, they often get amnesia. They can't remember what they said just a few minutes ago when they were speaking as one of their other personalities. I'll just note that often people with dissociative identity disorder are misdiagnosed as having schizophrenia because their beliefs are interpreted as a delusion. But I think more properly this could be interpreted as yet another demonstration that the brain has to go through an enormous amount of very delicate work to construct the self, and there are lots of ways this can be disrupted. Now, how can we study this? In the lab, one of my colleagues at Stanford, Joseph Parvizi, was studying patients with epilep see people who have electrical seizures in the brain. So one day one of his patients with APLEPSI tells him every time I have a seizure, I have a sense of depersonalization and dissociation. Everything's unreal, It's like it's not happening to me. And Parvez finds out that this patient's seizures started in a tiny brain area right in the brain's midline, called the anterior precuneus. And there was something very interesting about this area because it's not part of the default mode network, which I mentioned a moment ago, but instead it's a node at the center of a different network consisting of different areas. And this network integrates data about where you are and how you're moving, and where your muscles and joints are, so it's involved in building a mental map of your physical self. Now, just before I tell you more about this, one of the things I think is interesting is how parvs this ditinguishes between the I and the me. He says, Look, for every action we take, even during dreams, there's always an agent behind it. We call that agent I. But me is everything we have stored in our memories about the I. In other words, the eye has to do with your sense of your body in the immediate here and now, with a particular point of view, a first person perspective that belongs to only you. But the me, that's the narrative self, that has to do with actively or passively thinking about your past life or planning your future, things like memory and habits and personality, emotions, feelings for others, what lies ahead, and so on. Okay, now here's the key point from the brain's point of view. These two functions of the eye and the me, they're actually underpinned by separate networks of brain areas. These networks interact, they're not the same. So the me involving my memory, inhabits and personality and emotions, that mostly involves the default mode network. But the eye, which gives my sense of my particular point of view right now, that involves this other network where the anterior precunius sits at the center. And what Parvizi found is when that network becomes disrupted, let's say by an epileptic seizure that disrupts your self in the here and now. So he stuck electrodes into the anterior precuneus and zaps with electricity, and people say that something weird happens to their sense of physical self. They get a depersonalization, similar to what happens with psychedelics. It's not an out of body experience. People still feel like they're in their bodies, but they generally feel like there's a change in their orientation or their location, depending on where the stimulation happens. They feel like they're floating, your sinking, and it doesn't make any sense when they look around and they see where they are. And so their report was that the world around them seemed unreal. So again I want to be clear that you require this extraordinarily specific, delicate operation of multiple networks in the brain to make you feel a particular way, to give you an eye that's anchored in space with a point of view, and a me with a stable sense of who you are, and a connection to your memories and your sense as an individual. Now, assuming you have average good luck, then you'll never even be conscious of this perspective on the world. But if your brain gets disrupted from drugs or trauma or epilepsy, you're suddenly going to see it. Your world will seem unreal, and you'll come to understand that the self is a construction of the brain and needs all the pieces and parts to be running just right. Okay, so what we've talked about so far is the way the self can get disrupted. But now I want to switch gears to a less studied area. Instead of the dissolution of the self, I want to consider the expansion of the self. Now. I started thinking about this many years ago, even when I was a kid. I noticed that when you ride a bicycle, and maybe you accidentally, without meaning to, you run over a little worm that's crawled onto the sidewalk, and you recoil as though you'd physically stepped on the worm yourself with your bare feet, even though it was only the bicycle that touched the worm. So I started wondering if the bicycle becomes essentially a part of you, an extension of the self of some sort. And then when I got to college, I ended up reading some philosophers like Maurice Merleau Ponti and Gregory Bateson who posed a question like this about a blind man with a stick. The question was where does the blind man's self end and the rest of the world begin. You can think of the stick as like an extended cognitive system that pulls in information from the world. So does the blind man end at the handle of the stick or at the tip of the stick? Or does his self end somewhere in between? As Merleau Ponti wrote, quote, the blind man's cane has ceased to be an object for him. It's no longer perceived for itself. Rather, the caine's furthest point is transformed into a sensitive zone end quote. In other words, since the world is a deserved through the stick, it becomes part of the man's self. So humans alter the borders of their self all the time by using new instruments. I talked way back in episode two about dogs who learn how to ride skateboards, and even though wheels are not a part of the evolutionary history of canines, it becomes part of the dog. They become one with the skateboard, and I talked about surfing dogs even though the dog skeleton didn't evolve to be big and long and flat. The dog has no trouble incorporating the surfboard into its body plan into itsself. So we're not limited by the borders of our skin, but instead these self can expand. And I've also previously mentioned some experiments that were done years ago where a monkey learns to use a little rake to get some food that he couldn't otherwise reach. And once the monkey becomes proficient at this, there are cells in its brains sells that command actions and sells that sense what's going on. These cells change to include the rake in the space that they care about, what's known as their receptive field. In other words, the rake literally becomes part of the monkey. So whether we're talking about bicycle tires or walking canes for the blind, or the monkey and the rake, we see that the notion of the self has flexibility. It's not something that's just genetically pre programmed and fixed into place. So how does the body decide what to include what makes up the self? Well, in my last book, Live Wired, I proposed an answer to this. In part, it's about control. If the brain can control something, it becomes part of the self. So, for example, when my brain sends out signals to move my arm. My arm follows the commands, and therefore it becomes part of my self. The monkey's rake becomes part of what it can use and command in the world, so it becomes in a sense, part of its body. Now. Fundamentally, remember the brain is locked in silence and darkness, and so what does command mean to it? Fundamentally, it's all about prediction. Now. In an earlier episode forty four, we dove into the issue about the brain being a prediction machine. That's all it's trying to do. Locked in silence and darkness, It's trying to figure out what's happening in the world out there, And for really sophisticated brains like ours, it's not just about reacting to what happened, but instead having a model of the world that makes predictions about what will happen. So given this, what else can become a part of the cell. We are used to our brains controlling just our limbs, and this is because evolution has built us with muscle and tendons and nerves. But evolution never came up with controlling distant limbs via bluetooth. So in theory, if you could control a robotic arm with your brain, or a metal avatar that's all the way across town. This would become part of your self. And one question is what consequence would this have for your conscious experience. The answer is that the robot or the avatar would be perceived as a part of you. It would be another limb. It would be an unusual limb because of the physical gap between you and it, but it would nonetheless qualify as an extension of you. Think of the Avatar movies. The protagonist Jake Sully thinks of something he wants to do with his limited body, and the eight foot all avatar moves accordingly, and therefore the avatar becomes an extension of his self. By the way, you see this all the time. In the military. A soldier is in charge of driving a bomb sniffing robot, and everything the soldier commands with his joystick, the robot does. And at some point, if the robot gets blown up, it's not unusual to see one of these soldiers crying and heartbroken. It's like a part of them physically has been lost. Now, if this kind of extension of the self seems strange, just remember that you have everyday experience with this. Whenever you look in a mirror and move your body around, you see a distant object move in perfect synchrony with your motor commands. Your brain says, lift your arm, and you see this thing across the room, lift its arm. It's a perfect prediction. And so when you do that, you understand the reflection as your self. You don't feel any direct sensation from the distant limbs, but your brain registers the prediction. Every time I send out a command for X, that body over there does X, and that's enough for your reflection to become a member of the selfhood tribe. And one of the things I've written about recently is expanding oneself using virtual reality. You're in a virtual world and you raise your arm and you see your virtual avatar and the virtual mirror raise its arm. You tilt your head and it tilts its head. Now, interestingly, people are studying this in the context of empathy, because you can put someone else's face on the virtual avatar. Let's say someone of a different gender and a different race, and the question is how do you feel after having them be a part of you for a while. And you can experiment with very different kinds of bodies in VR. What if in a VR world you're one hundred feet tall, or you have eight legs or three arms. In all of these cases, you can learn to control that body, to predict what's happening, and then that body becomes you. The identity of the self is surprisingly flexible. So what I've proposed is that what the body can control becomes the self. And this all pivots on predictability, and so one tragic lesson we can glean from this is what happens when a person gets damage to their peripheral nerves so they can no longer control their limb. And what happens is they can get a disorder called asomatic nosea, which means they now deny ownership of the limb that they can't control. So as somatic nosia means not knowing one's body. And in the clinics you'll find the strangest things where somebody will say this leg does not belong to me, and sometimes they'll insist that the limb belongs to somebody else. They'll attribute the leg to, say a dead friend or a relative, or a phantasm or a devil, or one of the doctors taking care of them. They'll say the leg was sewn onto her, but it's not hers. She'll explain that her own real limb was stolen or is simply missing. And in variance of this disorder, people will sometimes construe the limb as an animal, perhaps like a snake, with its own independent life force and intentions. But the point is it's no longer a part of their self. So I was surprised when I found there was no gold standard explanation for this in the literature. But you'll have no trouble guessing my proposal, which is that the brain can no longer control the limb, and so the limb falls from the brotherhood of the self. By the way, sometimes these patients have a small window of lucidity in which they re recognize their limb as their own, but it doesn't last long. I hypothesize that this might result when the leg happens to move the way that they had intended accidental predictability. That might be a feeling of wanting to move the foot to the left, and then the foot happens to move that way, which leads the owner to take credit for the action. And given a person's lifelong experience of controlling her leg It should come as no surprise that even a temporary impression of control can snap it back into alignment with the self, even if just for a moment. So what you can predict becomes part of the self. Now. One of the places this becomes really interesting is with relationships, because when you come to know someone well, you in a sense expand yourself. They become a part of you. Again. This is because the brain is a prediction machine. You've spent a lot of time with the people in your life, and so you have rich predictions about them. You have increasingly sophisticated guesses about what they're going to do in some situation, and in this sense they become a part of you. Now, your predictions about other people are never going to be perfect, and those people will often surprise you. And so the degree to which your spouse or friend, your family member remains unpredictable is the degree to which she or he remains different from the self, remains independent from you. Nonetheless, they are, to a greater or lesser degree, a part of your brain's notion of the self, because you have some degree of prediction about them, and as a result, you can be proud of their accomplishments and feel happy when they're happy, and sad when they're sad. And part of what's hard about a breakup or the death of a loved one is it something like a self contraction. Okay, so now we're set up to return to the question that I posed at the beginning of the episode. Why do soldiers march in lockstep? And I think you can now guess my hypothesis. It's not just about intimidation, it's not just about discipline. It's about giving each soldier the usion of a larger self. If you are an individual soldier, you experience this expansion of the self, this enlargement because there are all these other bodies moving in a way that is precisely predictable by your brain. Your brain sends out motor commands that say, okay, stomp my right leg exactly now. And after that command goes out from the brain and down the spinal cord, it witnesses the power of a thousand legs, all stomping at the same moment. Your brain has sent out a command, and you feel the earthshake as a result. It's empowering to be part of a group because your self now consists of thousands of bodies. There are a dozen ways to look at this issue of marching in lockstep socially, but from the neuroscience point of view, when you do stuff in synchrony with others, there's an expansion of the brain's construction of this self. So this is my hypothesis for why we see so much synchronization around us. You see this in Japanese festivals where everyone is doing the same thing at the same time. Or take the Hodge, which is this annual Islamic pilgrimage to Mecca. You've got pilgrims from all over the world travel to Mecca to flow around this big cube at the center of the Grand Mosque. Is very stunning to see hundreds of thousands of bodies swirling like a larger mega organism. And this is typical of religious ritual. If you only knew neuroscience and knew nothing about societal behavior, you might predict the existence of this sort of thing because the commands from each pilgrim's brain is multiplied by the feedback from hundreds of thousands of other pilgrims, and that kind of feedback is intoxicating to human brains. And as I said, you find this sort of synchronization in all religious rituals. Everyone is doing the same thing at the same time, ideally in the same costume. And I propose that it's not accidental everyone stands and sits at the same time, or genuflex or chants. When you look across religions, I suspect that the details of the rituals don't matter much at all. Instead, it's the allure of learning how to fuse your identity with a larger group. You think, wow, I can learn the steps, the moves, the words here and be part of a larger self. That is the promise that is being offered to you. You never find religious rituals where everything is desynchronized, where the promise is come into my religion, where we each do our own thing. You walk in whenever you want, you face wherever you want, Everyone sing and chant out of tune. You just don't see religions where there's no bigger voice, no bigger self acting in unison. And of course you find exactly the same synchronization in non religious ceremonies. One hypothesis about the origin of music and dancing is that this came from early primates who would synchronize with one another, and when we dance, we see this. If you're an observer of human behavior, it's hard to ignore that humans love to be synchronized on the dance floor. And you can imagine a bunch of early primates sitting around and all banging rocks together, making shouts or chants that aren't random but synchronized. You can see how the drive for a larger self could be at the root of this. And when you start looking for humans synchronizing, you see it everywhere. You see it in group exercise classes like yoga or dance or aerobics. Everyone's doing the same thing at the same time, and that synchronization fosters this sense of unity. You get the same thing in choirs where everyone sings together, or at music concerts, where the crowds synchronize their movements to the rhythm of the music. They sway, they clap, they sing along together. At sports events, you have fans synchronize their chance just like a protest marches. What's happening if you're at the event is that your brain sends commands to your larynx with the prediction that it will hear your voice in return. But now you hear your voice times a thousand, and you feel like your self is larger and more powerful. So let's wrap this up. My interest is in this question of where does your self end and others begin? And although you think you end at the borders of your skin, you're actually a flexible creature, extending past what you can see and feel, incorporating it tooferent times, your family, your partners, your teams, the culture in which you're embedded. And I think looking at this from the neuroscience point of view is a very powerful way to understand rituals and dancing inquires and religious ceremonies. Even on the political scale. It might shed light on our study of in groups and outgroups, and our understanding of things like patriotism. And this all fundamentally comes down to an extension of this self, which always reminds me to question, what would happen if you were born in a different culture, a different neighborhood, a different era in time. Would you be you? Presumably not in a way that we would recognize. You are wired up by the world that you happen to be in. All of it, to a lesser or greater degree, becomes part of what your brain considers your self. So I'm fascinated with this question of how we draw the limits of our selves. For example, I'm thinking some thoughts, and I jot notes throughout the week, and I go into my studio and record this podcast, and you listen to it. But it might be a week later after I've recorded it, or maybe you are listening to this long after I'm dead, and yet we're still communicating. I'm taking ideas from my head and capturing them in zeros and ones stored on a server somewhere, and eventually that gets transmitted over the Internet or maybe in a century, over Internet twelve to your device, and then my words reach you, and you're suddenly connected with me. I'm right next to you, I'm in your ear, I'm in your brain. My words make physical changes to the networks inside your head. And if we're alive at the same time, you can send me an email and I read the words on the screen that you wrote, and we are connected. And with our current communication technologies, this is more true than ever that our brains have the opportunity to expand the self, from literature to television, to podcasts to the Internet. We increasingly have the opportunity to become larger than we would otherwise be. Please visit eagleman dot com slash podcast for more information and to find further reading. Send me an email at podcast at eagleman dot com with questions or discussion, and check out and subscribe to Inner Cosmos on YouTube for videos of each episode and to leave comments. Until next time, I'm David Eagleman and this is Inner Cosmos