Ep44 "Why can't you tickle yourself?" (Time Traveling Part 2)

around us? Welcome to Inner Cosmos with me David Eagleman. I'm a neuroscientist and author at Stanford and in these episodes we sail deeply into our three pound universe to understand why and how our lives look the way they do. Today's episode is about one of the most important things that brains do, which is the simulation of possible futures.

The way we teach about brains in the classroom usually has to do with the brain figuring out where it is and what is happening around it, Like it detects touch on its skin, and it detects photons from the environment out there, and it picks up on sound waves that are happening, and it stitches all of these together in the massive hurricane of electrical spikes that race around in the silence and darkness of your skull, and all of this neural information allows you to put together a

picture of what is happening in the world out there, and that is what allows you to operate in the world and to catch that fish and put it in your mouth, and to run from the predator, or more hosaically, to find the right empty parking space, or tell the cashier what you want from the fast food menu, or apply the brakes on your bicycle when there's a pothole in the road. So the brain gathers data from the world around it so that it can operate inside of

that world. But what we talked about last week was something surprising, which is that the brain doesn't spend all of its time in the present. In fact, a lot of its experiences are not in the here and now at all, but instead in the past. Your brain holds on to data about previous events in your life. In other words, what happened and who was there, and what the spatial configuration of the furniture was in the room, and the building, and you spend quite a lot of

your time recalling that past. This whole process is what we summarize as memory. And what I emphasized last week is that we spend a good deal of our existence unhooked from the here and now, and instead we time travel to that past. But why do we care about the past? This is for one reason only. We do it to better simulate possible futures, and that's what today's episode is about. It turns out we spend an enormous amount of our time traveling to the future. Our time

travel is not one way, it goes both directions. We simulate possibilities. We think of what our actions could lead to. If I say this, then my spouse might say this other thing back to me. If I open this cabinet over here, I will expect to find soup cans in there. If I do XYZ, I'll impress my boss, and I'll hope to get that promotion. We walk down long paths

of possible chess moves that we can play in our lives. So, as I said, we spend the vast majority of our lives not in the here and now, but in the there, and then in either direction. We spend most of our days in daydreams and stories and confabulations in life narratives of reminiscence and future projection. When you tally all this up, the years that we spend in the realm of fantasy outstrip the time that we spend in the present. So

why do we simulate the future? Well, first, it's much more energy efficient to do that than to try everything out in the real world. If I have to haul this rock over there, I can sit and simulate several possible approaches. I can imagine myself picking it up and carrying it over there. But then I realized, now I'll never be able to get it o over that big gulch. Well, thank goodness that I ran that simulation from the comfort

of sitting on the ground and thinking about it. That's super energy efficient, and I can try out different methods of hauling the rock. What if I use a rope or a wheelbarrow or a catapult. I can try out all these different things without breaking a sweat or burning any calories besides the few calories required for simulation, which is orders of magnitude less than employing my muscles to move my multi trillion cell body. Around in the world, and this kind of simulation, this is what we humans

do all the time. So imagine you are a fire chief and you and your team roll up on a new fire that's engulfing a building. Your job is to quickly make predictions about how to best position your team. So, given your past experience with the world, you mentally simulate different layouts and you evaluate their effectiveness, and then once you've simulated a great plan or the best of what's available,

then you set it into action. In the real world, you don't have to try out every single thing in the physical world, and it's not just about energy efficiency. More generally, the reason you simulate possible futures is because it's much less dangerous than trying everything out in the real world. So let's say you're parked in your car and you need to go to some door, but there is a dog barking at you, So you run a movie.

You simulate what would it be like if I make a run for that door, and your brain might run that and decide, you know what, that's not worth the risk. So your brain simulates other plans, like maybe you stay in the car and you dial the owner, or maybe you crack the window and you yell for the owner. Things like that, your brain doesn't actually have to run

the risk of confronting the dog. Or maybe some big guy cuts in front of you when you're waiting in line, and you might simulate all kinds of things that you want to do to him in including calling him names or pushing him in the back or whatever. But you are usually better running the simulations in your head and not taking advantage of all the things that you could do.

As the philosopher Carl Popper put it, simulation of the future allows our hypotheses to die in our stead, So intelligent brains do not want to engage in the expensive and potentially fatal game of physically testing every action to figure out what the consequences are. Instead, it is more efficient and safer when possible to envisage consequences of a

proposed plan before you actually execute it. So by learning up the rules of the world and simulating possible outcomes and evaluating each one of them, your brain can play out scenarios without the risk and expense of attempting them physically. For this reason, prediction of possible futures is one of

the highest priorities of biological systems. Now, fascinatingly, there hasn't been that much direct study of how brains do this, mostly because of the difficulty of observing it in action, because the whole purpose of mental simulation is to make action unnecessary, and the traditional way that we study the brain is to correlate something in the brain with an action and explicit behavior. So this is what makes it

challenging to study simulation of the future. Nonetheless, what I'm gonna tell you about today is the way that we can pull together scattered data to begin to understand how brains build possible worlds. So let's get started. The important place to start is with an idea that I've talked about a lot on this podcast, the idea of the

internal model. The idea is that the brain's job isn't just about detecting and reacting in real time, but it's about constructing a model on the inside about what's happening in the outside world. It's like you're running a simulation there in the silence and the darkness of the brain. And the key is that the internal model can emulate possible scenarios. Now, one of the first places that we see this kind of simulation get studied is with our

physical interactions with the world. For example, think about when you hold a ketchup bar bottle in your left hand and you pound it with your right hand to try to get the ketchup to come out onto your French fries. Now, when you do that, your left arm doesn't move very much when you pound with your right hand because your

muscles tighten up. But just the right moment. Now, if you want to try an interesting experiment, just hold the ketchup bottle and have a friend pound the bottle, and what you'll see is that your arm moves a lot.

You can't keep your arm still when somebody else is hitting the bottle, But when you hit it, you are the one making the action, and your brain knows how to simulate what's about to happen in this case, that there's about to be a lot of pressure on your arm, and so it can deal in real time with counterbalancing. That This is the brain predicting something simple that hasn't actually happened yet. Your hand is about to hit the bottle and your arm tenses up in expense. Now, why

does the brain care about prediction? Well, if your brain can simulate things into the future that can speed up your response time. And this is really useful for potentially dangerous things, like if you need to dodge a rock that's being thrown at you, or if you need to catch some prey and you can figure out where it's heading. This reminds us, of course, of the great hockey player Wayne Gretzky, who said, I skate to where the puck

is going to be, not to where it has been. Now, you don't have to be Wayne Gretzky for your brain to be predicting the next step of everything around you. Why, because your brain's architecture is built to anticipate everything in advance. How does it do this Well, First, your nervous system doesn't just send out motor commands like move your arm. It also sends out copies of that motor command along other telegraph wires to let other parts of the brain

know that the command was just sent out. So this is what's called an efference copy, and that has all kinds of effects on what happens next. For example, when you move your eyes around, your eyes are jumping about three times per second. The world seems to remain stable visually and This is because of the efference copy that tells the rest of your brain, okay, visual cortex, get ready. The whole world is about to streak past to the left.

So your visual cortex, which is locked in darkness, isn't surprised when the eyes suddenly make a jump and the data is now all different. Now contrast that with what happens if you get a friend to gently push your eyeball from the outside. Now, the visual world appears to shift. In the first case, when you are moving your eyes voluntarily, the eference copy tells the brain, hey, a move is

coming up, and that suppresses visual motion detection. But in the second case, when somebody pushes your eye, the absence of an effherence copy means, hey, that movement isn't mine, it's external, And so you perceive visual motion in the world. And I'll give you another example. What happens every time you blink your eyes. When you do that, for about a tenth of a second, the world goes dark. But you don't perceive that because you know it is coming.

Your brain systems that send out the command to blink the eyelids also let the visual system know, hey, this is what's about to happen. This way, your visual cortex can anticipate that's about to happen, so the blink gets ignored. Now, if you don't believe me, maybe you think the blink is just too fast or something like that. Just sit in a room and have your friend flick the light switch really fast so that everything goes dark for a

tenth of a second. You can't miss that. It's really obvious since it wasn't you that caused the darkness, you notice it. So, as we see with the ketchup bottle and eye movements and blinks, brains make predictions about the consequences of your own actions. And a great example of this is tickling. It turns out that if someone is coming after you and sticking their fingers under your underarms, it makes you laugh uncontrollably. It tickles. But I don't

know if you've ever tried this. It turns out you're not able to tickle yourself. Why not, It's because of the simple fact that your own actions are predictable by your brain. You can't surprise your left underarm with your right hand because your brain is the one driving the fingers of the right hand, and it determines exactly when to move the fingers, and so there is zero surprise when the left underarm senses that for tickling, you require unpredictability.

That's the whole trick to a tickle. When people study this with brain imaging fMRI, they find that when you try to tickle yourself, you get activity in the primary somatosensory cortex, meaning your brain is detecting that there's a feeling there. But the activity doesn't go further. It doesn't activate all these other downstream areas that come online when someone else is tickling you, like the secondary somatosensory cortex and the anterior singular cortex. Your brain sees the tickle

coming and discounts it. In fact, other neuroimaging studies find that these brain areas that come online when you're getting tickled, these same areas become active when you are simply anticipating a tickle. When somebody's fingers are moving close, your somatis sensory areas start to go to town. Now it turns out there is one way that you can tickle yourself, and that is if you build a little device that inserts randomness so you can no longer predict the tickle.

So imagine you set up a little machine where you are moving a lever around like a joystick, and that controls a feather that tickles your left underarm. But in between the movement of the lever and the movement of the feather, the computer injects random time delays. That way, your brain can't know when the movement in your under is going to occur. And now you rescue the tickle. With the help of a little bit of technology, you

can tickle yourself. Importantly, it also turns out there is one group of people who are able to tickle themselves, and that is people who are suffering from schizophrenia. So in episode thirty three, I talked about my hypothesis that schizophrenia might be in part or in whole a disorder of time perception. So in this light, it's very instructive that people with schizophrenia can tickle themselves. This suggests that they're unable to predict their own actions and how those

actions will lead to the next sensations. This inability to understand one's own actions, this is a general deficit that we see in schizophrenia. People will have a hard time distinguishing things they call from things they didn't cause. A person with schizophrenia will say something like, my hand picks up the paper clip, but I'm not the one controlling my hand. What my hand does has nothing to do with me. And of course you've heard of things like

auditory hallucinations in schizophrenia. In that other episode, I talked about how we all have an internal dialogue. You generate a voice and you listen to it, and in schizophrenia, the timing seems to be slightly off such that the internal voice gets attributed to somebody else. Interestingly, my colleague Chris Frith and his collaborators ran a study with people who had schizophrenia, and they found that if a person has schizophrenia but does not have auditory hallucinations, then they

are more ticklish when other people tickle them. But if a person with schizophrenia does have auditory hallucinations, then they can tickle them themselves. They judge no difference between someone else tickling them and them tickling themselves. They are no longer making the appropriate predictions. Okay, so this gives us a sense of how our brains, under normal circumstances work

to constantly make predictions. And it's not just about predicting things about your own actions and sensations, but more generally about anything to do with the outside world. And the key is that our brains are not simply reactive, but they have these internal loops that are constantly making predictions about what comes next. And having this kind of architecture it allows brains to do not just stimulus response, but

instead to make predictions ahead of actual sensory input. So think about trying to catch a baseball that someone is tossing to you. If your brain was just doing feed forward analysis of these signals, you couldn't catch the ball. There'd be a delay of hundreds of milliseconds from the time that the light strikes your eye until you could execute the motor command of putting your hand up, and your hand would always be reaching for a place where

the ball used to be. We are able to catch baseballs because we have deeply hardwired internal models of physics, and these internal models generate expectations about when and where the ball is going to hit. It's making predictions about the future. Now, how does this sort of prediction play out in your daily life? Because it's not just about hitting catch a bottles and catching baseballs. But prediction applies to every decision you make about what you're going to do.

Let's say you're trying to figure out what you need to do in an hour from now. You have a bunch of things on your to do list, but given the constraints of space and time, you can't do everything at once, and so life is a constant series of choices. So let's say you're looking at these choices. One you have to write a very long and specific email for

your boss. Two you're thinking of going downtown to get a boba tee, or three you're considering going to the gym, which you've been promising yourself that you're going to do for some days now. So how does the choice actually get made in the brain. As far as our conscious minds go, we get very little access to the details. It just seems like, oh, okay, I've decided to do this instead of that, but you don't necessarily know why.

But the last several decades of neuroscience have surfaced how this actually happenins We run the simulations and we feel them. So when you think about writing that email, your brain actually runs the little movie of you doing that, and possibly the ache that you might feel in your shoulder from typing too much, and also the satisfaction at finishing that task. Then your brain runs the simulation of going and getting the boba t how delicious that will be

and how satisfying it'll be. And you also run the simulation of going to the gym. It's gonna be a little costly for you in terms of time, and it might make your muscles hurt, but boy, are you gonna feel great when you're done. You'll feel so satisfied. Now, what happens is your brain runs all these simulations and you feel the emotions with each one. Now again, this happens essentially entirely under the hood. For most of the

decisions you make in life. You have no conscious access to how you made the final call, But your brain is simulating the possibilities, and you experience each one with your emotions and often with physical sensations. And this is how we weigh choices against one another. This is how we determine our paths in life. You feel the pain or the pleasure from your predicted futures. You think of yourself in future times, and you get to live out

those little movies. Now like everything in our brains. We think this just automatically works, but in fact we have very particular networks that need to be in place and

working well for this to function. And the reason we know this is because some people get damage to a part in the front of their brain, the venture medial prefrontal cortex, and they end up displaying a very strange and unexpected symptom, which is, if you give them some choice to make, like which restaurant do you want to go to tonight, they can articulate everything about the decision, but they can't decide. They can't land on a decision.

So what's going on here? Well, patients like this have been studied by neurologists like Antonio Demacio and his colleagues, and what's happening is that their brain can run a quick future simulation, but it has become disconnected from the emotions. So the different future simulations all feel the same way. They all feel neutral, and therefore there's no way to distinguish any choice from any other. In other words, you need to feel the outcome of a simulation in order

to do decision making. So it turns out that under normal circumstances, there's a core network of brain areas that are involved in prospect, which just means seeing ahead. So I want to give you a very quick sense of this. So you've got this area of your brain, the venture medial prefrontal cortex, which connects to areas involved in emotion like the anterior insula and the amignla, and it also

connects to lots of other areas in the brain. And activity in this area essentially specifies the things that are pertinent to your current needs and goals, and this is what guides the construction of relevant scenarios. Now, there are a number of other brain areas that show up in this core network. One is called the precuneus, and this maps the locations of things in space, so its involvement contributes to a spatial context for imagine scenarios and the

features inside of that. There's another area called the temporopridal junction, and you see that area become active during the detection of targets or events around you that are relevant to what you're trying to do at this moment. This area seems to run and do the same thing even in your imagined scenarios. And then you've got an area called the superior temporal sulcus, which is involved with lots of things,

but one of them is about interpreting social cues. So one idea is that this area helps to specify other individuals in their actions within imagined scenes. And then you have the hippocampus. And one thing that's known is that when you get damage to the hippocampus, that seems to mess up all of the spatial coherence of a recalled or imagined scene. So patients with hippocampal damage they can't picture a specific place or detailed surrounding events. Here's one way to think about this.

like the VR goggles would. So this all suggests that the hippocampus is crucial for tying together the activity of other brain areas to construct this rich and coherent imaginary experience. You have this brainwide network of areas that are involved when you are imagining future scenarios, and all of this is what helps you to experience the movie and to

feel the emotions. If you are just a robot who rolled into a room, you would just sit there because you wouldn't have any particular reason to prioritize writing the email versus getting the Boba tee versus going to the gym. You would have no way to weigh these against one another. But we assign feeling to all of our future scenarios. So the brain makes predictions. But how does it know

how to improve these through time. Well, imagine a fire department in a city, and every time a fire occurs in the city, they go wailing out of the station to take care of it, and they suspect that a lot of the fires are going to happen around the warehouse district, so they put their trucks there so they can take care of things quickly. But eventually they realize that their prediction was wrong. It's actually another part of

the city that keeps catching fire. So the area at the foot of the mountains where the trees are dense and interwoven with power lines, So the fire department starts putting their resources there where they need to be in advance, and that reduces the energy they need to expend every time there's a new fire because they're no longer being reactive to fires at the foot of the mountain, but

now they're making good predictions about it. So cities do this kind of thing, by the way, in terms of fires, in terms of where they expect crime is going to occur, in terms of where and when the power usage is going to happen. Everything. So the key about this example is that the fire department's first predictions weren't so great, and the data tells them, oh, that could be a lot better. It tells them that something could be adjusted. And that is the same thing that happens in the

brain all the time. The brain tries to predict everything, and it pays attention to what's called the prediction error, which means the difference between what it thought would happen and what actually happened. And you see various cells in the brain, for example, in the dopamine system that are responding not to the reward or punishment, but the prediction error. In other words, how different the reward or punishment was

from what was expected. And these dopamine systems broadcast their signals all across the territory of the brain to announce that the prediction wasn't quite right, there was a prediction error, and therefore something needs to be adjusted. So our brain has the architecture to make predictions and adjust them all the time. And what is all this architecture of the brain tell us. It tells us that the brain craves predictability. Now why does it care about predictability? Well, first of

all because of energy efficiency. Because if you can predict that something is going to happen, then you don't have to burn up all this neural energy on it. You already know it's coming. But if something is a surprise, the brain turns its vast attentional mechanisms to it and has to burn a lot of calories on understanding what the heck just happened and eventually reshaping the internal model to account for that. In the future, all of this

would be fine. Maybe if we could plug ourselves into a wall, but instead we are mobile creatures who run on batteries. We have to constantly find food sources and stick them in our mouth so that we can have enough energy to get to the next food source. So mother nature evolved us to be highly efficient creatures. And what we do is we make ourselves massively efficient by predicting away the future. And this is, by the way, why the method of torture referred to as the Chinese

water torture is so aversive to us. The idea is that a drop of cold water drips onto your head, and then let's say five seconds later, the next draw hits, and then the next one three seconds later, and then the next drop eight seconds slater, and the next one six seconds slater, and then four seconds and suddenly one second,

and you get the idea. It's unpredictable. Your brain is constantly trying to say when an event is going to happen, and it's constantly having to pay attention here because it can't make a good prediction. And perhaps you've never experienced that form of torture explicitly that most of us have at some point in our lives, had a leaky faucet at our house, and this can often be just as bad if it never falls into a rhythm, it goes drip, drip, drip. We love rhythm because we can predict it away, and

anything that is unpredictable continues to demand all our attention. Now, I'll just mention that my colleagues and I have proposed in various places that maybe the brain activity that we see, the spikes and neurons, these represent just the part of the world that is unpredicted. In other words, silence is golden, and the brain spends most of its efforts trying to make perfect predictions of the world and burn that down into the circuitry of the brain so it doesn't have

to use any activity. Now, of course, of course, the world is way too complicated to ever reach perfect prediction. Everything changes all the time, and so the speculation is that the activity that we can measure in the brain, whether that's with electrodes or fMRI or whatever, really that activity just represents the surprise, the thing that the brain

didn't see coming. In other words, if you show a yellow ball to a monkey and you find cells in his brain, say in the visual cortex that respond vigorously to that visual thing, then we say those cells prefer yellow balls, or more colloquially, we say it likes the yellow ball. But could it just be that the appearance of a yellow ball was unpredicted by the system and

the cells activity is merely a reflection of that. This is consistent with the fact that if you hide the ball and then reshow it to the monkey five seconds later, and then you do that again and again, the response diminishes. This is known as repetition suppression, and it's not merely about fatigue of the cell. Instead, it's the fact that the monkey's brain knows that you're about to show the stupid ball again, and so it has a prediction of what is coming. And when it knows what is coming,

it doesn't have to burn any energy. We'll come back to this in terms of our deep desired to have predictions about our lives in just a few moments. But first I want to ask can species other than human beings engage in prospection and imagination? This question is difficult to answer because animals can't verbally report their experiences to us.

Some researchers think, well, maybe animals lack the capacity for this sort of thing, but in fact they do share much of the same circuitry that we've been talking about, and careful observation their behavior suggests that they have some features of episodic memory and prospection. For example, look at the scrubjay, which is a bird that stores food away. It can recall not just where it hit a particular item,

but also what that item was and when it was stored. Now, skeptics say, okay, look, maybe this is just procedural memory. It's like a basic algorithm that's running. It's not conscious, and it's just driven by the needs of the moment. But the scrub jays also appear to cash food in a way that reflects anticipated future needs. It's not just their current motivational state. And when you look at rats, when people do direct recordings of the hippocampus, that suggests

that they too might engage in prospection and recollection. So as a rat move through adjacent places, you have these hippocampal play cells that fire off in sequences, and these play cells sometimes replay the activity sequence when the rat is not moving, sometimes even when the rat is sleeping after the experiment is over, and these cells can also pre play a sequence of activity before the rat has

started to move along the route. So, for example, if the rat has to go down a hallway and then turn right or left, this is called a te maze, and it's trying to decide which path to take. You can see these play cells pre play one route and then the other, as if in consideration of both these scenarios. Now, this research is still early, but these kinds of findings might increasingly point us in the direction of at least roughly gauging whether our animal cuts and have internal experiences

of time travel the way that we do. So what I've told you so far is how the brain predicts. But how does it know how to do this? How does it make good predictions about the world. So suppose you're hungry and you decide you're going to get something to eat. Where should you go? You need to have a map in your head of all the nearby choices. Then you have to decide which one would most likely

satisfy your current craving. And so to plan your excursion you need to go through your past experiences of meals and the places on your map. So you've got that inexpensive tie restaurant which is the closest, but the food there you remember, was too spicy for your taste. And the food truck over there they make great burritos, but it always has a really long line in your past experience. And the fast food joint over here has fries that are a little greasy, but you'd rather take the grease

than the spice or the long lines. So, putting together the experiences of your recalled past and your imagined future, you decide on your option. But the past and the future are intertwined in most of our decisions. In other words, the thing that allows the brain to construct possible futures is memory. Memory is what allows us to write down information and then use that as building blocks to build out our future scenarios. Now, interestingly, that's not even a

new idea. Aristotle suspected this, as did Galen and all their medieval commentators. They all emphasized memory as the key tool in making successful predictions for the future. And in fact, something that I find very interesting, presumably coincidental but maybe not, is that in Greek mythology, the goddess of memory, Nemazine, is the mother of the nine muses, who are the goddesses who spark the imagination. In other words, memory is

the mother of imagination. Now, my friend and colleague Jeff Hawkins made the argument that what we call intelligence boils down to the brain's ability to make good predictions about the world based on stored memories. In his version of the memory prediction paradigm, the cortex is a pattern recognition

machine that breaks complicated events into smaller bunks. It stores experiences in a way that reflects the structure of the world, and then it's springboards off these known experiences to make predictions. As Hawkins puts it, intelligence is the capacity of the

brain to predict the future by analogy to the past. Now, fascinatingly, in two thousand and seven, Demisesabis and his colleagues at London's Institute of Neurology made this really striking observation that patience who had damage to their hippocampus not only had amnesia for past experiences, but also couldn't imagine new ones. So if you ask a patient with this brain damage to remember his past, he can't do that, and we expected that. But now you ask him to imagine the future,

and he just can't do it. You ask him to imagine standing in a museum full of exhibits and he'll say something like there's not a lot coming, I'm not picturing anything. Or you might say, hey, look, imagine going on a vacation to the beach. Really picture yourself lying there on the beach, and describe the scene to me. And the person might be able to say, well, there's a blue sky, or maybe they describe an isolated sound,

but that's it. Otherwise they just draw a blank. And by the way, if you provide the person with pictures and sounds and smells to help them along, that doesn't help them to imagine the scene. So unlike a healthy control, the patient with hippocampal damage just can't simulate any vivid details. It's not like an episode to them the way that your imagination is. Their descriptions, if they exist at all,

are very unspecific. So the healthy control can describe a spatial layout and people being present, and descriptions of the smells and sights and sounds, thoughts and emotions they might have, and actions they might take. But the patient with the hippocampal damage can't do any of that. At best. What they're able to come up with has a lack of spatial coherence. The imagined experience is just a collection of

fragmentary sensations instead of a unified episode. In a particular setting, you can ask them what they'll see if they go over to a shopping mall, or what they might want to eat if they go to a restaurant, and they just draw a blank. They can only put together a few details that are not well connected. So the deficits in their memories apply to their simulations of the future as well. Now, how do we understand this in terms

of the circuitry. Well, the key came from brain imaging studies in the past two decades, which have uncovered that there's a network of regions involved both for remembering the past and imagining new ones. It's the same areas, so the hippocampus and its surrounding area. That's one part of this, but we also find several other areas like the medial, prial cortex and prefront areas, and the lateral, temporal and lateral pride lobes. All these regions are important for elaborating

on the details of imagined and also for remembered episodes. So, in other words, the brain's episodic memory systems, which we discussed in the last episode, are just as important for imagining future experiences. In other words, this core network underlies mental time travel in either direction. So this leads to a really interesting thought about something, which is that if recall of the past and simulation of the future both use the same network, then maybe what we mean by

memory is something more like simulation. So I want to propose this hypothesis that memories are not the fundamental thing, but instead simulation is the fundamental thing, and memories are just a special type of simulation. A memory is merely a simulation that's pinned down to always flow a particular way. And if this is the right way to look at it, maybe what we call remembrance we will someday call resimulation. So instead of dividing the territory into memory and prediction,

they may in fact be one thing. Any context is run through a simulation to predict the outcome. So brains simulate possible futures, and we constantly function by making predictions about everything in our lives and our communities and our nation and the world. But I want to be clear that even though we use the word prediction, there's no guarantee of accuracy. We are actually pretty bad at capturing the future. As the baseball catcher Yogi Bearra said, it's

tough to make predictions, especially about the future. Why is it tough. It's because we only simulate based on our experience in the world. So if you've never seen something before, you're going to have a pretty bad prediction about it. For example, futurists make all kinds of predictions about the next decade or two, and most of them turn out to be wrong. In one study of famous forecasters, it was found that their predictions were between ten to fifty

percent accuracy, which certainly isn't that great. But it's not just futurists. It's all of us, with most of our predictions about our lives, and by the way, our inability to see the future, well, this is why we have the existence of magicians or mystery writers or scam artists. These are people who take advantage of the fact that our ability to predict the future is not very good. The magician knows that we're going to predict the location

of the object incorrectly and then will be surprised. The mystery novelist knows that he can lead us down a garden path and that we will extrapolate incorrectly in the direction that he wants us to, so we don't correctly see what's going to happen. The scam artist does the same thing, but in real life, getting our brains to see a vision of success that doesn't actually match with

what's going to happen. Now, I'll just note something here, which is that's sometimes our inability to make good predictions that helps us. So take the origin of the Oxford English Dictionary, where a professor who loved words said, you know what, I'm going to write down a definition for every word there is. This can't take very long, especially if I recruit help from others, which he did. But despite an insane amount of work, the Oxford English Dictionary

finally got finished eighty years after his death. He would have never started it had he been a good predictor. So there's something useful about our optimism bias in the form of our bad predictions. Now, we've all experienced this kind of bad prediction on smaller levels, where we assume that some task is going to take us less time

than it actually does. We also experience this on the level of most of our life trajectories, where we think, all right, I generally know where my life is going, but if you look back at any decade of your life, you'll realize that your predictions generally weren't so good. Why it's because the only way we can make predictions is by leveraging our memories what has all ready happen to us.

The memories serve as building blocks, and all we're able to do is use those building blocks to make versions of the future, which is really just an edifice constructed of the bricks that we've seen before. And that's why we are so inherently limited in seeing what's coming. And there's a very specific way that we're terrible at predicting the future. We generally assume the future will just be

a straightforward extension of the present in our lives. We assume that we have changed up to this point, but we're going to remain about like this from here on out. For example, when people think back to their childhoods, they see lots of change in their own bodies and personalities and beliefs, and also in the technology that surrounds them. But when people are asked to think about the future, they generally assume everything is going to be roughly this

same as it is now. Maybe you'll have a little more gray hair, maybe your electric car will have a longer range, but that's about it. We feel like we've arrived after a steep path and now the world will mostly stay fixed as it is. So we think things are going to stay as they are. And nowhere is

this more true than with our predictions about technology. The fact is, the world is changing faster than ever as a result of the law of accelerating returns, which simply says that the more technology advances, the faster the next

generation of technology is going to advance. And we find ourselves now at the cusp of such fundamental revolutions, not only artificial intelligence, but also nanotech and biotech and quantum computing and room temperature superconductivity and energy storage and genetic engineering and on and on. All of these things going to weave together in ways that we can't currently imagine. And we are standing on an exponential curve that's about to rise at a steeper slope than we've ever seen,

but we can't see it clearly coming. Why again, it's because we rely on our memories to paint our vision of the future, so our predictions are limited to remixes of our past, which makes it really difficult to anticipate the significant disruptions heading our way. And there's one other issue here for our lives, because we're always trying to make good predictions and therefore save brain energy. We really

hate change. I mentioned before how we don't like the dripping faucet because it's unpredictable, But this hatred of the unpredictable applies to everything, including being told that things will change in the future, like climate change. Climate change makes people very anxious because you look at a map of the world and you see that over the next x number of decades people will be shifting around as temperatures increase. And we hate that because fundamentally we feel most comfortable

if things stay exactly the way they are. Like you want to imagine that your house, which is exactly two hundred and fifty seven feet from the shore of the ocean, will remain precisely where it is centuries from now, But of course it won't, even if you put aside everything about man made pollution. The shorelines always change. Where I live in California, the beach used to extend miles farther out.

I'm talking about fourteen thousand years ago, and when the ice Age ended and the glaciers melted, the sea level rose and ate up all of that beach. And that's why we don't find coastal settlements from the first people from Asia who came across cross the bearing Land Bridge and settled here fourteen thousand years ago. Things were totally different at that time. For example, there was no San Francisco Bay. There was no water there that was all

locked up in glaciers. When any of us who live here look at the San Francisco Bay, we imagine it's permanent, but of course it's not. If you were one of the first settlers in North America, the place would have looked very different to you. You could have walked across from what is now the city of San Francisco over to Alcatraz without getting a single drop of water on your feet. It's easy to study geography retrospectively and say, wow,

that's interesting. But when we look in the forward direction, we get very anxious at the thought that populations of people will move around and borders will change. Now that's not to minimize what's happening with climate change, but it is to say that change has always happened. I mean, the last little ice Age just ended in eighteen fifty, where for five hundred years it was two degrees colder in Europe and mountain glaciers expanded and people had to

move around. The only issue I'm pointing to here is that even though the world has always changed, we want it to stay stable now. We fundamentally want to imagine the future of the world looking exactly as we know it now. And you can see this as easily at small scales as you do on the large scales. For example, in this past month, there have been a new round of company layoffs in Silicon Valley, and this makes people

so nervous and anxious. Now, most people who have lost a job end up saying later that they're happy because it opens up new opportunities for them and exposes them to things they didn't even know. They didn't know and they realized there was more out there to be experienced in the world. And yet the change itself proves very hard for people in the moment. It's as though their brains are screaming out for everything to stay exactly the

same as it was. Why, Because we are creatures who try to predict Our brains are designed to do that to save energy, and the most anxiety producing thing for the accuracy of our predictions is when the world itself changes out from under you. As an example, I've been on the boards of many organizations. When somebody resigns and so much trauma for the board, there's a long discussion

about how to keep the organization together. Everybody's feelings are bubbling, and then the conversation eventually turns to how this presents a real opportunity for us to mix things up, to inject new blood, to do things in a way that's no longer stale. It's fascinating to watch the conversation always follow the same trajectory, as though everyone is reading from

a script. It reminds me of a notion from The Simpsons where Homer is anxious about something and Lisa, his daughter, says, look on the bright side, Dad, Did you know that the Chinese use the same word for crisis as they do for opportunity, and Homer says, yes, chrisis as tunity. The point is that change of any sort presents a crisis to the predictive systems of the brain, but it is eventually seen as an opportunity. The bottom line is that we get used to the world and we don't

want things to change. So, given that our predictive ability is not so great and that we don't want things to change, how did we ever become so successful as a species. Well, the first answer is science. When it comes to predicting big issues in the real world, our intuitions just aren't up for the task. Our brains always make predictions, but human brains are small and they're not nearly as good as groups of brains working together, and the scientific method simply gives us away a set of

rules for working together to find the most accurate predictions. Fundamentally, that's all science is figuring out the rules so we can best predict the future. But I want to highlight what I propose is a second reason that humans got really good at predicting the future, and this is perhaps a more surprising reason why our species has become a runaway species, and that reason is storytelling. So literature like stories, novels,

and movies. This is critically important for the success of our species because we can take one person's imagined stories something they've worked out all the pieces and parts of over a long time, and that author can make that scenario real for us, He can reify it. So stories allow us to experience possible futures. Just think, for example, of the nineteen eighties movie The Day After. It was about nuclear war and what it is to wake up the day after America has been turned to rubble by

nuclear bombs. It took something that required an unusually rich imagination and it allowed us to see it, to experience a situation that otherwise would have remained purely conceptual. And this is why stories are so important. They allow us to live in worlds that we otherwise would not, and then that gives us new memories that we can use as new building blocks to see a little farther out

than we would have otherwise. In this sense, literature allows us to get out of our heads and share the creative headspace of someone else who has thought down a particular path, probably in great detail, and then we get to enjoy that person's guidance. And the key, as far as we can tell, is that other species, for example, hippopotamuses don't tell stories around the campfire. And it's not just hippopotamuses, but every other one of the millions of

species of animals on this earth. We have no evidence that any of them tells stories. So the way I think about this is that they just have a lot less practice expanding beyond their own limited experience of the world. But we spend a ton of our time imagining what's not there. We are mental time travelers, and we use other people's stories and books to get there. The class that I'm teaching at Stanford this quarter is Literature and

the Brain. What I find so extraordinary about the active reading is that we use a string of symbols to fire up this whole imagination engine and to have us live through scenarios. And I propose that we have come to beat out every animal species on the planet, including lions and tigers and bears, all of whom could tear us to shreds easily. We have beat them out because of stories. We have these fierce animals in our zoos in every city, and they have no humans in their zoos.

It's not just about guns and spears, it's about planning. We can capture them because we can outthink them. So I posed at the beginning of the episode a question, what would I advise the president if we found ourselves at war with extraterrestrials. Well, here's what If we land on a planet with fierce bug like creatures, we shouldn't worry too much about their capacity to be anything but reactive. We will probably be able to trick them, to outflank them,

to outthink them. But if we discover that these creatures also have life libraries, we should quietly turn around and sneak away, because it means they have exposed themselves to thousands of other worlds beyond what they could otherwise experience, and that cognitive practice makes them potentially a very wily opponent. The degree to which an alien species has literature will tell us how good they are at predicting possible futures and developing rich scenarios of what ifs. It allows them

to expand their experiences far beyond a single head. So let's wrap up what we saw today is that brains simulate possible futures, and brains do this by relying on the lessons of the past. This makes your memory the mother of your imagination, just like the goddess of memory gave birth to the muses. Now, in the last two episodes, we've talked about running simulations in the backward direction, which we call memory, and running them in the forward direction,

which is how we envision possible futures. But everything I've told you so far is just a setup, because that is just the beginning. Come back next week to see how now we can leverage this concept of time travel to deeply understand why our mental lives are as nuanced and colorful and complex as they are simulating. Next week, I'm David Eagleman, and this is Inner Cosmos. In the meantime, go to eagleman dot com slash podcast for more information

and to find further reading. Send me an email at podcasts at eagleman dot com with questions or discussion, and I'll be making episodes in which I address those until next time. Thank you for joining me in the outermost reaches of the Inner Cosmos