WEBVTT - Ep44 "Why can't you tickle yourself?" (Time Traveling Part 2) 0:00:05.040 --> 0:00:10.680 Why can't you tickle yourself? Why don't hippopotamuses tell stories 0:00:10.840 --> 0:00:15.800 around the campfire? What would I advise the president if 0:00:15.840 --> 0:00:20.120 we find ourselves at war with extraterrestrials? And what does 0:00:20.160 --> 0:00:23.560 any of this have to do with Wayne Gretzky or 0:00:23.800 --> 0:00:28.400 the Greek Goddess of Memory and her children? Or poking 0:00:28.440 --> 0:00:31.280 your finger into the side of your eyeball, or hitting 0:00:31.360 --> 0:00:34.440 a bottle to get ketchup onto your French fries? And 0:00:34.560 --> 0:00:37.520 why do we get so anxious about the world changing 0:00:37.680 --> 0:00:44.519 around us? Welcome to Inner Cosmos with me David Eagleman. 0:00:45.000 --> 0:00:48.840 I'm a neuroscientist and author at Stanford and in these 0:00:48.880 --> 0:00:52.680 episodes we sail deeply into our three pound universe to 0:00:52.800 --> 0:00:57.080 understand why and how our lives look the way they do. 0:01:05.280 --> 0:01:08.560 Today's episode is about one of the most important things 0:01:08.640 --> 0:01:14.559 that brains do, which is the simulation of possible futures. 0:01:15.880 --> 0:01:18.560 The way we teach about brains in the classroom usually 0:01:18.600 --> 0:01:22.120 has to do with the brain figuring out where it 0:01:22.200 --> 0:01:25.280 is and what is happening around it, Like it detects 0:01:25.360 --> 0:01:28.480 touch on its skin, and it detects photons from the 0:01:28.600 --> 0:01:31.160 environment out there, and it picks up on sound waves 0:01:31.160 --> 0:01:34.360 that are happening, and it stitches all of these together 0:01:34.920 --> 0:01:38.840 in the massive hurricane of electrical spikes that race around 0:01:38.880 --> 0:01:42.920 in the silence and darkness of your skull, and all 0:01:43.000 --> 0:01:46.720 of this neural information allows you to put together a 0:01:46.760 --> 0:01:49.920 picture of what is happening in the world out there, 0:01:50.280 --> 0:01:53.240 and that is what allows you to operate in the 0:01:53.280 --> 0:01:56.120 world and to catch that fish and put it in 0:01:56.120 --> 0:02:00.720 your mouth, and to run from the predator, or more hosaically, 0:02:00.800 --> 0:02:04.640 to find the right empty parking space, or tell the 0:02:04.680 --> 0:02:07.760 cashier what you want from the fast food menu, or 0:02:07.920 --> 0:02:10.639 apply the brakes on your bicycle when there's a pothole 0:02:10.680 --> 0:02:14.400 in the road. So the brain gathers data from the 0:02:14.400 --> 0:02:17.760 world around it so that it can operate inside of 0:02:17.800 --> 0:02:21.640 that world. But what we talked about last week was 0:02:21.680 --> 0:02:25.679 something surprising, which is that the brain doesn't spend all 0:02:25.720 --> 0:02:29.680 of its time in the present. In fact, a lot 0:02:29.720 --> 0:02:33.480 of its experiences are not in the here and now 0:02:33.639 --> 0:02:38.600 at all, but instead in the past. Your brain holds 0:02:38.639 --> 0:02:42.280 on to data about previous events in your life. In 0:02:42.320 --> 0:02:46.680 other words, what happened and who was there, and what 0:02:46.720 --> 0:02:50.000 the spatial configuration of the furniture was in the room, 0:02:50.120 --> 0:02:53.560 and the building, and you spend quite a lot of 0:02:53.600 --> 0:02:58.480 your time recalling that past. This whole process is what 0:02:58.520 --> 0:03:02.919 we summarize as memory. And what I emphasized last week 0:03:03.440 --> 0:03:06.799 is that we spend a good deal of our existence 0:03:06.880 --> 0:03:09.720 unhooked from the here and now, and instead we time 0:03:09.919 --> 0:03:13.919 travel to that past. But why do we care about 0:03:13.960 --> 0:03:17.840 the past? This is for one reason only. We do 0:03:17.960 --> 0:03:24.240 it to better simulate possible futures, and that's what today's 0:03:24.320 --> 0:03:27.440 episode is about. It turns out we spend an enormous 0:03:27.480 --> 0:03:31.200 amount of our time traveling to the future. Our time 0:03:31.280 --> 0:03:34.679 travel is not one way, it goes both directions. We 0:03:35.200 --> 0:03:40.440 simulate possibilities. We think of what our actions could lead to. 0:03:41.720 --> 0:03:44.080 If I say this, then my spouse might say this 0:03:44.160 --> 0:03:47.040 other thing back to me. If I open this cabinet 0:03:47.080 --> 0:03:50.280 over here, I will expect to find soup cans in there. 0:03:50.720 --> 0:03:54.280 If I do XYZ, I'll impress my boss, and I'll 0:03:54.280 --> 0:03:59.600 hope to get that promotion. We walk down long paths 0:03:59.680 --> 0:04:03.600 of possible chess moves that we can play in our lives. So, 0:04:03.680 --> 0:04:05.760 as I said, we spend the vast majority of our 0:04:05.800 --> 0:04:08.080 lives not in the here and now, but in the there, 0:04:08.320 --> 0:04:11.760 and then in either direction. We spend most of our 0:04:11.880 --> 0:04:18.440 days in daydreams and stories and confabulations in life narratives 0:04:18.480 --> 0:04:23.920 of reminiscence and future projection. When you tally all this up, 0:04:24.040 --> 0:04:27.719 the years that we spend in the realm of fantasy 0:04:27.920 --> 0:04:31.600 outstrip the time that we spend in the present. So 0:04:32.200 --> 0:04:37.919 why do we simulate the future? Well, first, it's much 0:04:38.000 --> 0:04:42.320 more energy efficient to do that than to try everything 0:04:42.400 --> 0:04:45.400 out in the real world. If I have to haul 0:04:45.560 --> 0:04:50.440 this rock over there, I can sit and simulate several 0:04:50.680 --> 0:04:55.080 possible approaches. I can imagine myself picking it up and 0:04:55.200 --> 0:04:59.000 carrying it over there. But then I realized, now I'll 0:04:59.000 --> 0:05:01.880 never be able to get it o over that big gulch. Well, 0:05:02.160 --> 0:05:06.240 thank goodness that I ran that simulation from the comfort 0:05:06.360 --> 0:05:08.560 of sitting on the ground and thinking about it. That's 0:05:08.680 --> 0:05:12.920 super energy efficient, and I can try out different methods 0:05:12.920 --> 0:05:15.599 of hauling the rock. What if I use a rope 0:05:15.839 --> 0:05:19.960 or a wheelbarrow or a catapult. I can try out 0:05:20.440 --> 0:05:25.119 all these different things without breaking a sweat or burning 0:05:25.200 --> 0:05:31.000 any calories besides the few calories required for simulation, which 0:05:31.040 --> 0:05:35.719 is orders of magnitude less than employing my muscles to 0:05:36.040 --> 0:05:40.560 move my multi trillion cell body. Around in the world, 0:05:41.960 --> 0:05:44.719 and this kind of simulation, this is what we humans 0:05:44.800 --> 0:05:48.919 do all the time. So imagine you are a fire 0:05:49.040 --> 0:05:51.400 chief and you and your team roll up on a 0:05:51.440 --> 0:05:55.279 new fire that's engulfing a building. Your job is to 0:05:55.360 --> 0:06:00.479 quickly make predictions about how to best position your team. So, 0:06:00.600 --> 0:06:05.120 given your past experience with the world, you mentally simulate 0:06:05.200 --> 0:06:09.360 different layouts and you evaluate their effectiveness, and then once 0:06:09.440 --> 0:06:13.799 you've simulated a great plan or the best of what's available, 0:06:14.240 --> 0:06:17.120 then you set it into action. In the real world, 0:06:17.600 --> 0:06:21.480 you don't have to try out every single thing in 0:06:21.520 --> 0:06:26.280 the physical world, and it's not just about energy efficiency. 0:06:26.880 --> 0:06:31.720 More generally, the reason you simulate possible futures is because 0:06:31.800 --> 0:06:36.240 it's much less dangerous than trying everything out in the 0:06:36.279 --> 0:06:39.159 real world. So let's say you're parked in your car 0:06:39.200 --> 0:06:41.000 and you need to go to some door, but there 0:06:41.120 --> 0:06:44.440 is a dog barking at you, So you run a movie. 0:06:44.480 --> 0:06:46.840 You simulate what would it be like if I make 0:06:46.880 --> 0:06:50.800 a run for that door, and your brain might run 0:06:50.839 --> 0:06:53.279 that and decide, you know what, that's not worth the risk. 0:06:53.440 --> 0:06:56.240 So your brain simulates other plans, like maybe you stay 0:06:56.279 --> 0:06:58.480 in the car and you dial the owner, or maybe 0:06:58.520 --> 0:07:01.240 you crack the window and you yell for the owner. 0:07:01.320 --> 0:07:04.480 Things like that, your brain doesn't actually have to run 0:07:04.520 --> 0:07:08.880 the risk of confronting the dog. Or maybe some big 0:07:08.920 --> 0:07:11.160 guy cuts in front of you when you're waiting in line, 0:07:11.560 --> 0:07:14.520 and you might simulate all kinds of things that you 0:07:14.560 --> 0:07:17.480 want to do to him in including calling him names 0:07:17.560 --> 0:07:19.920 or pushing him in the back or whatever. But you 0:07:19.960 --> 0:07:24.480 are usually better running the simulations in your head and 0:07:24.600 --> 0:07:27.840 not taking advantage of all the things that you could do. 0:07:28.600 --> 0:07:32.520 As the philosopher Carl Popper put it, simulation of the 0:07:32.600 --> 0:07:40.400 future allows our hypotheses to die in our stead, So 0:07:40.800 --> 0:07:45.880 intelligent brains do not want to engage in the expensive 0:07:46.120 --> 0:07:51.320 and potentially fatal game of physically testing every action to 0:07:51.400 --> 0:07:55.160 figure out what the consequences are. Instead, it is more 0:07:55.200 --> 0:08:00.600 efficient and safer when possible to envisage consequences of a 0:08:00.680 --> 0:08:06.160 proposed plan before you actually execute it. So by learning 0:08:06.240 --> 0:08:10.440 up the rules of the world and simulating possible outcomes 0:08:10.440 --> 0:08:14.280 and evaluating each one of them, your brain can play 0:08:14.320 --> 0:08:19.880 out scenarios without the risk and expense of attempting them physically. 0:08:20.280 --> 0:08:24.280 For this reason, prediction of possible futures is one of 0:08:24.320 --> 0:08:30.440 the highest priorities of biological systems. Now, fascinatingly, there hasn't 0:08:30.480 --> 0:08:34.240 been that much direct study of how brains do this, 0:08:34.559 --> 0:08:39.360 mostly because of the difficulty of observing it in action, 0:08:40.120 --> 0:08:44.680 because the whole purpose of mental simulation is to make 0:08:44.840 --> 0:08:49.720 action unnecessary, and the traditional way that we study the 0:08:49.760 --> 0:08:54.120 brain is to correlate something in the brain with an 0:08:54.280 --> 0:08:58.320 action and explicit behavior. So this is what makes it 0:08:58.720 --> 0:09:02.880 challenging to study simulation of the future. Nonetheless, what I'm 0:09:02.920 --> 0:09:04.600 gonna tell you about today is the way that we 0:09:04.640 --> 0:09:09.520 can pull together scattered data to begin to understand how 0:09:09.640 --> 0:09:15.360 brains build possible worlds. So let's get started. The important 0:09:15.400 --> 0:09:17.800 place to start is with an idea that I've talked 0:09:17.800 --> 0:09:20.280 about a lot on this podcast, the idea of the 0:09:20.480 --> 0:09:25.559 internal model. The idea is that the brain's job isn't 0:09:25.640 --> 0:09:29.480 just about detecting and reacting in real time, but it's 0:09:29.480 --> 0:09:34.600 about constructing a model on the inside about what's happening 0:09:34.679 --> 0:09:38.480 in the outside world. It's like you're running a simulation 0:09:38.720 --> 0:09:41.880 there in the silence and the darkness of the brain. 0:09:42.679 --> 0:09:46.600 And the key is that the internal model can emulate 0:09:46.960 --> 0:09:50.440 possible scenarios. Now, one of the first places that we 0:09:50.559 --> 0:09:54.000 see this kind of simulation get studied is with our 0:09:54.120 --> 0:09:58.240 physical interactions with the world. For example, think about when 0:09:58.280 --> 0:10:01.560 you hold a ketchup bar bottle in your left hand 0:10:01.840 --> 0:10:04.760 and you pound it with your right hand to try 0:10:04.760 --> 0:10:08.440 to get the ketchup to come out onto your French fries. Now, 0:10:08.480 --> 0:10:12.439 when you do that, your left arm doesn't move very 0:10:12.559 --> 0:10:15.440 much when you pound with your right hand because your 0:10:15.559 --> 0:10:18.720 muscles tighten up. But just the right moment. Now, if 0:10:18.720 --> 0:10:21.080 you want to try an interesting experiment, just hold the 0:10:21.120 --> 0:10:25.840 ketchup bottle and have a friend pound the bottle, and 0:10:25.880 --> 0:10:28.839 what you'll see is that your arm moves a lot. 0:10:28.960 --> 0:10:32.640 You can't keep your arm still when somebody else is 0:10:32.720 --> 0:10:35.959 hitting the bottle, But when you hit it, you are 0:10:36.000 --> 0:10:38.960 the one making the action, and your brain knows how 0:10:38.960 --> 0:10:42.760 to simulate what's about to happen in this case, that 0:10:42.800 --> 0:10:45.240 there's about to be a lot of pressure on your arm, 0:10:45.800 --> 0:10:49.480 and so it can deal in real time with counterbalancing. 0:10:49.559 --> 0:10:53.880 That This is the brain predicting something simple that hasn't 0:10:53.920 --> 0:10:57.240 actually happened yet. Your hand is about to hit the 0:10:57.280 --> 0:11:02.120 bottle and your arm tenses up in expense. Now, why 0:11:02.160 --> 0:11:06.120 does the brain care about prediction? Well, if your brain 0:11:06.200 --> 0:11:10.079 can simulate things into the future that can speed up 0:11:10.400 --> 0:11:14.400 your response time. And this is really useful for potentially 0:11:14.480 --> 0:11:17.679 dangerous things, like if you need to dodge a rock 0:11:17.760 --> 0:11:20.160 that's being thrown at you, or if you need to 0:11:20.640 --> 0:11:23.960 catch some prey and you can figure out where it's heading. 0:11:24.559 --> 0:11:27.720 This reminds us, of course, of the great hockey player 0:11:27.800 --> 0:11:31.880 Wayne Gretzky, who said, I skate to where the puck 0:11:32.120 --> 0:11:37.559 is going to be, not to where it has been. Now, 0:11:37.559 --> 0:11:39.760 you don't have to be Wayne Gretzky for your brain 0:11:39.840 --> 0:11:43.520 to be predicting the next step of everything around you. Why, 0:11:43.880 --> 0:11:50.800 because your brain's architecture is built to anticipate everything in advance. 0:11:51.320 --> 0:11:55.400 How does it do this Well, First, your nervous system 0:11:55.480 --> 0:11:59.640 doesn't just send out motor commands like move your arm. 0:12:00.160 --> 0:12:05.160 It also sends out copies of that motor command along 0:12:05.280 --> 0:12:08.920 other telegraph wires to let other parts of the brain 0:12:09.080 --> 0:12:12.679 know that the command was just sent out. So this 0:12:12.720 --> 0:12:16.200 is what's called an efference copy, and that has all 0:12:16.320 --> 0:12:21.880 kinds of effects on what happens next. For example, when 0:12:21.920 --> 0:12:25.120 you move your eyes around, your eyes are jumping about 0:12:25.200 --> 0:12:29.679 three times per second. The world seems to remain stable 0:12:29.880 --> 0:12:34.480 visually and This is because of the efference copy that 0:12:34.600 --> 0:12:38.880 tells the rest of your brain, okay, visual cortex, get ready. 0:12:38.920 --> 0:12:42.199 The whole world is about to streak past to the left. 0:12:43.120 --> 0:12:46.720 So your visual cortex, which is locked in darkness, isn't 0:12:46.800 --> 0:12:50.520 surprised when the eyes suddenly make a jump and the 0:12:50.640 --> 0:12:55.120 data is now all different. Now contrast that with what 0:12:55.280 --> 0:12:58.559 happens if you get a friend to gently push your 0:12:58.600 --> 0:13:03.439 eyeball from the outside. Now, the visual world appears to shift. 0:13:04.480 --> 0:13:07.920 In the first case, when you are moving your eyes voluntarily, 0:13:08.440 --> 0:13:12.040 the eference copy tells the brain, hey, a move is 0:13:12.080 --> 0:13:16.440 coming up, and that suppresses visual motion detection. But in 0:13:16.480 --> 0:13:20.640 the second case, when somebody pushes your eye, the absence 0:13:20.760 --> 0:13:24.760 of an effherence copy means, hey, that movement isn't mine, 0:13:24.800 --> 0:13:28.960 it's external, And so you perceive visual motion in the world. 0:13:29.679 --> 0:13:32.760 And I'll give you another example. What happens every time 0:13:32.840 --> 0:13:36.920 you blink your eyes. When you do that, for about 0:13:36.960 --> 0:13:40.400 a tenth of a second, the world goes dark. But 0:13:40.520 --> 0:13:43.640 you don't perceive that because you know it is coming. 0:13:43.720 --> 0:13:47.240 Your brain systems that send out the command to blink 0:13:47.280 --> 0:13:51.600 the eyelids also let the visual system know, hey, this 0:13:51.640 --> 0:13:55.160 is what's about to happen. This way, your visual cortex 0:13:55.280 --> 0:14:00.400 can anticipate that's about to happen, so the blink gets ignored. Now, 0:14:00.480 --> 0:14:02.640 if you don't believe me, maybe you think the blink 0:14:02.720 --> 0:14:05.360 is just too fast or something like that. Just sit 0:14:05.400 --> 0:14:08.160 in a room and have your friend flick the light 0:14:08.240 --> 0:14:11.040 switch really fast so that everything goes dark for a 0:14:11.080 --> 0:14:14.079 tenth of a second. You can't miss that. It's really 0:14:14.160 --> 0:14:19.120 obvious since it wasn't you that caused the darkness, you 0:14:19.680 --> 0:14:23.960 notice it. So, as we see with the ketchup bottle 0:14:24.000 --> 0:14:28.040 and eye movements and blinks, brains make predictions about the 0:14:28.120 --> 0:14:33.120 consequences of your own actions. And a great example of 0:14:33.160 --> 0:14:37.520 this is tickling. It turns out that if someone is 0:14:37.560 --> 0:14:41.359 coming after you and sticking their fingers under your underarms, 0:14:41.560 --> 0:14:46.240 it makes you laugh uncontrollably. It tickles. But I don't 0:14:46.240 --> 0:14:49.400 know if you've ever tried this. It turns out you're 0:14:49.480 --> 0:14:54.880 not able to tickle yourself. Why not, It's because of 0:14:54.920 --> 0:14:59.600 the simple fact that your own actions are predictable by 0:14:59.640 --> 0:15:04.920 your brain. You can't surprise your left underarm with your 0:15:05.000 --> 0:15:08.480 right hand because your brain is the one driving the 0:15:08.560 --> 0:15:11.880 fingers of the right hand, and it determines exactly when 0:15:11.920 --> 0:15:15.600 to move the fingers, and so there is zero surprise 0:15:16.120 --> 0:15:23.760 when the left underarm senses that for tickling, you require unpredictability. 0:15:23.840 --> 0:15:27.960 That's the whole trick to a tickle. When people study 0:15:28.000 --> 0:15:32.040 this with brain imaging fMRI, they find that when you 0:15:32.240 --> 0:15:36.760 try to tickle yourself, you get activity in the primary 0:15:36.840 --> 0:15:40.840 somatosensory cortex, meaning your brain is detecting that there's a 0:15:40.880 --> 0:15:44.320 feeling there. But the activity doesn't go further. It doesn't 0:15:44.360 --> 0:15:49.120 activate all these other downstream areas that come online when 0:15:49.200 --> 0:15:53.680 someone else is tickling you, like the secondary somatosensory cortex 0:15:53.760 --> 0:15:59.000 and the anterior singular cortex. Your brain sees the tickle 0:15:59.160 --> 0:16:05.120 coming and discounts it. In fact, other neuroimaging studies find 0:16:05.520 --> 0:16:08.680 that these brain areas that come online when you're getting tickled, 0:16:09.040 --> 0:16:13.320 these same areas become active when you are simply anticipating 0:16:13.320 --> 0:16:17.600 a tickle. When somebody's fingers are moving close, your somatis 0:16:17.600 --> 0:16:21.880 sensory areas start to go to town. Now it turns 0:16:21.920 --> 0:16:26.120 out there is one way that you can tickle yourself, 0:16:26.680 --> 0:16:29.400 and that is if you build a little device that 0:16:29.560 --> 0:16:34.840 inserts randomness so you can no longer predict the tickle. 0:16:35.240 --> 0:16:38.000 So imagine you set up a little machine where you 0:16:38.080 --> 0:16:41.560 are moving a lever around like a joystick, and that 0:16:41.600 --> 0:16:46.080 controls a feather that tickles your left underarm. But in 0:16:46.160 --> 0:16:49.240 between the movement of the lever and the movement of 0:16:49.280 --> 0:16:55.920 the feather, the computer injects random time delays. That way, 0:16:56.360 --> 0:16:59.840 your brain can't know when the movement in your under 0:17:00.400 --> 0:17:04.720 is going to occur. And now you rescue the tickle. 0:17:05.080 --> 0:17:07.719 With the help of a little bit of technology, you 0:17:07.760 --> 0:17:13.199 can tickle yourself. Importantly, it also turns out there is 0:17:13.600 --> 0:17:17.520 one group of people who are able to tickle themselves, 0:17:17.600 --> 0:17:22.080 and that is people who are suffering from schizophrenia. So 0:17:22.119 --> 0:17:25.040 in episode thirty three, I talked about my hypothesis that 0:17:25.080 --> 0:17:30.040 schizophrenia might be in part or in whole a disorder 0:17:30.080 --> 0:17:34.240 of time perception. So in this light, it's very instructive 0:17:34.280 --> 0:17:39.879 that people with schizophrenia can tickle themselves. This suggests that 0:17:39.920 --> 0:17:44.600 they're unable to predict their own actions and how those 0:17:44.640 --> 0:17:49.720 actions will lead to the next sensations. This inability to 0:17:49.960 --> 0:17:53.560 understand one's own actions, this is a general deficit that 0:17:53.600 --> 0:17:56.879 we see in schizophrenia. People will have a hard time 0:17:57.640 --> 0:18:01.560 distinguishing things they call from things they didn't cause. A 0:18:01.680 --> 0:18:05.639 person with schizophrenia will say something like, my hand picks 0:18:05.720 --> 0:18:08.280 up the paper clip, but I'm not the one controlling 0:18:08.280 --> 0:18:11.679 my hand. What my hand does has nothing to do 0:18:11.760 --> 0:18:14.800 with me. And of course you've heard of things like 0:18:15.160 --> 0:18:20.200 auditory hallucinations in schizophrenia. In that other episode, I talked 0:18:20.200 --> 0:18:24.400 about how we all have an internal dialogue. You generate 0:18:24.440 --> 0:18:27.320 a voice and you listen to it, and in schizophrenia, 0:18:27.760 --> 0:18:30.920 the timing seems to be slightly off such that the 0:18:30.960 --> 0:18:37.640 internal voice gets attributed to somebody else. Interestingly, my colleague 0:18:37.720 --> 0:18:41.840 Chris Frith and his collaborators ran a study with people 0:18:41.840 --> 0:18:44.959 who had schizophrenia, and they found that if a person 0:18:45.600 --> 0:18:50.359 has schizophrenia but does not have auditory hallucinations, then they 0:18:50.359 --> 0:18:54.000 are more ticklish when other people tickle them. But if 0:18:54.000 --> 0:18:59.320 a person with schizophrenia does have auditory hallucinations, then they 0:18:59.359 --> 0:19:03.359 can tickle them themselves. They judge no difference between someone 0:19:03.440 --> 0:19:07.359 else tickling them and them tickling themselves. They are no 0:19:07.480 --> 0:19:29.560 longer making the appropriate predictions. Okay, so this gives us 0:19:29.560 --> 0:19:33.480 a sense of how our brains, under normal circumstances work 0:19:33.600 --> 0:19:37.760 to constantly make predictions. And it's not just about predicting 0:19:37.880 --> 0:19:41.840 things about your own actions and sensations, but more generally 0:19:42.320 --> 0:19:45.600 about anything to do with the outside world. And the 0:19:45.720 --> 0:19:49.359 key is that our brains are not simply reactive, but 0:19:49.440 --> 0:19:54.440 they have these internal loops that are constantly making predictions 0:19:54.840 --> 0:19:59.360 about what comes next. And having this kind of architecture 0:20:00.000 --> 0:20:04.000 it allows brains to do not just stimulus response, but 0:20:04.040 --> 0:20:09.160 instead to make predictions ahead of actual sensory input. So 0:20:09.200 --> 0:20:12.159 think about trying to catch a baseball that someone is 0:20:12.240 --> 0:20:16.600 tossing to you. If your brain was just doing feed 0:20:16.760 --> 0:20:20.800 forward analysis of these signals, you couldn't catch the ball. 0:20:20.840 --> 0:20:24.320 There'd be a delay of hundreds of milliseconds from the 0:20:24.359 --> 0:20:27.919 time that the light strikes your eye until you could 0:20:28.200 --> 0:20:31.840 execute the motor command of putting your hand up, and 0:20:32.040 --> 0:20:34.440 your hand would always be reaching for a place where 0:20:34.480 --> 0:20:37.480 the ball used to be. We are able to catch 0:20:37.520 --> 0:20:43.119 baseballs because we have deeply hardwired internal models of physics, 0:20:43.520 --> 0:20:47.520 and these internal models generate expectations about when and where 0:20:47.960 --> 0:20:51.480 the ball is going to hit. It's making predictions about 0:20:51.800 --> 0:20:56.160 the future. Now, how does this sort of prediction play 0:20:56.200 --> 0:20:59.200 out in your daily life? Because it's not just about 0:20:59.359 --> 0:21:04.240 hitting catch a bottles and catching baseballs. But prediction applies 0:21:04.400 --> 0:21:07.960 to every decision you make about what you're going to do. 0:21:08.720 --> 0:21:11.000 Let's say you're trying to figure out what you need 0:21:11.040 --> 0:21:12.760 to do in an hour from now. You have a 0:21:12.800 --> 0:21:15.720 bunch of things on your to do list, but given 0:21:15.760 --> 0:21:18.520 the constraints of space and time, you can't do everything 0:21:18.560 --> 0:21:23.520 at once, and so life is a constant series of choices. 0:21:23.920 --> 0:21:26.199 So let's say you're looking at these choices. One you 0:21:26.800 --> 0:21:29.399 have to write a very long and specific email for 0:21:29.440 --> 0:21:33.400 your boss. Two you're thinking of going downtown to get 0:21:33.400 --> 0:21:37.720 a boba tee, or three you're considering going to the gym, 0:21:37.800 --> 0:21:40.000 which you've been promising yourself that you're going to do 0:21:40.040 --> 0:21:43.000 for some days now. So how does the choice actually 0:21:43.000 --> 0:21:46.520 get made in the brain. As far as our conscious 0:21:46.640 --> 0:21:49.440 minds go, we get very little access to the details. 0:21:49.440 --> 0:21:52.040 It just seems like, oh, okay, I've decided to do 0:21:52.480 --> 0:21:55.080 this instead of that, but you don't necessarily know why. 0:21:55.920 --> 0:21:59.080 But the last several decades of neuroscience have surfaced how 0:21:59.160 --> 0:22:05.800 this actually happenins We run the simulations and we feel them. 0:22:06.160 --> 0:22:09.520 So when you think about writing that email, your brain 0:22:09.600 --> 0:22:12.919 actually runs the little movie of you doing that, and 0:22:13.000 --> 0:22:16.080 possibly the ache that you might feel in your shoulder 0:22:16.160 --> 0:22:20.040 from typing too much, and also the satisfaction at finishing 0:22:20.080 --> 0:22:24.160 that task. Then your brain runs the simulation of going 0:22:24.240 --> 0:22:28.240 and getting the boba t how delicious that will be 0:22:28.440 --> 0:22:32.280 and how satisfying it'll be. And you also run the 0:22:32.320 --> 0:22:35.680 simulation of going to the gym. It's gonna be a 0:22:35.760 --> 0:22:38.439 little costly for you in terms of time, and it 0:22:38.520 --> 0:22:41.080 might make your muscles hurt, but boy, are you gonna 0:22:41.080 --> 0:22:45.360 feel great when you're done. You'll feel so satisfied. Now, 0:22:45.400 --> 0:22:49.080 what happens is your brain runs all these simulations and 0:22:49.160 --> 0:22:53.320 you feel the emotions with each one. Now again, this 0:22:53.400 --> 0:22:57.080 happens essentially entirely under the hood. For most of the 0:22:57.680 --> 0:23:01.240 decisions you make in life. You have no conscious access 0:23:01.240 --> 0:23:04.840 to how you made the final call, But your brain 0:23:05.000 --> 0:23:08.840 is simulating the possibilities, and you experience each one with 0:23:08.920 --> 0:23:13.439 your emotions and often with physical sensations. And this is 0:23:13.600 --> 0:23:18.280 how we weigh choices against one another. This is how 0:23:18.600 --> 0:23:22.320 we determine our paths in life. You feel the pain 0:23:22.440 --> 0:23:25.919 or the pleasure from your predicted futures. You think of 0:23:26.000 --> 0:23:30.200 yourself in future times, and you get to live out 0:23:30.240 --> 0:23:35.120 those little movies. Now like everything in our brains. We 0:23:35.359 --> 0:23:38.960 think this just automatically works, but in fact we have 0:23:39.560 --> 0:23:43.239 very particular networks that need to be in place and 0:23:43.320 --> 0:23:46.520 working well for this to function. And the reason we 0:23:46.640 --> 0:23:50.359 know this is because some people get damage to a 0:23:50.560 --> 0:23:52.879 part in the front of their brain, the venture medial 0:23:52.920 --> 0:23:57.399 prefrontal cortex, and they end up displaying a very strange 0:23:57.400 --> 0:24:00.240 and unexpected symptom, which is, if you give them some 0:24:00.359 --> 0:24:03.040 choice to make, like which restaurant do you want to 0:24:03.080 --> 0:24:07.280 go to tonight, they can articulate everything about the decision, 0:24:07.880 --> 0:24:12.000 but they can't decide. They can't land on a decision. 0:24:12.720 --> 0:24:15.840 So what's going on here? Well, patients like this have 0:24:15.920 --> 0:24:20.440 been studied by neurologists like Antonio Demacio and his colleagues, 0:24:21.040 --> 0:24:24.720 and what's happening is that their brain can run a 0:24:24.960 --> 0:24:31.120 quick future simulation, but it has become disconnected from the emotions. 0:24:31.280 --> 0:24:35.680 So the different future simulations all feel the same way. 0:24:35.680 --> 0:24:38.719 They all feel neutral, and therefore there's no way to 0:24:38.920 --> 0:24:43.720 distinguish any choice from any other. In other words, you 0:24:43.840 --> 0:24:47.760 need to feel the outcome of a simulation in order 0:24:47.840 --> 0:24:52.480 to do decision making. So it turns out that under 0:24:52.520 --> 0:24:57.679 normal circumstances, there's a core network of brain areas that 0:24:57.720 --> 0:25:02.960 are involved in prospect, which just means seeing ahead. So 0:25:03.000 --> 0:25:04.800 I want to give you a very quick sense of this. 0:25:05.840 --> 0:25:08.119 So you've got this area of your brain, the venture 0:25:08.200 --> 0:25:12.720 medial prefrontal cortex, which connects to areas involved in emotion 0:25:13.560 --> 0:25:16.760 like the anterior insula and the amignla, and it also 0:25:16.920 --> 0:25:19.960 connects to lots of other areas in the brain. And 0:25:20.160 --> 0:25:24.000 activity in this area essentially specifies the things that are 0:25:24.119 --> 0:25:27.600 pertinent to your current needs and goals, and this is 0:25:27.640 --> 0:25:34.080 what guides the construction of relevant scenarios. Now, there are 0:25:34.080 --> 0:25:36.199 a number of other brain areas that show up in 0:25:36.240 --> 0:25:40.160 this core network. One is called the precuneus, and this 0:25:40.400 --> 0:25:44.520 maps the locations of things in space, so its involvement 0:25:45.000 --> 0:25:50.520 contributes to a spatial context for imagine scenarios and the 0:25:50.960 --> 0:25:56.480 features inside of that. There's another area called the temporopridal junction, 0:25:56.760 --> 0:26:00.320 and you see that area become active during the detection 0:26:01.080 --> 0:26:04.720 of targets or events around you that are relevant to 0:26:04.760 --> 0:26:08.879 what you're trying to do at this moment. This area 0:26:08.920 --> 0:26:11.679 seems to run and do the same thing even in 0:26:11.800 --> 0:26:16.360 your imagined scenarios. And then you've got an area called 0:26:16.400 --> 0:26:20.200 the superior temporal sulcus, which is involved with lots of things, 0:26:20.240 --> 0:26:24.239 but one of them is about interpreting social cues. So 0:26:24.320 --> 0:26:28.520 one idea is that this area helps to specify other 0:26:28.880 --> 0:26:34.439 individuals in their actions within imagined scenes. And then you 0:26:34.520 --> 0:26:38.159 have the hippocampus. And one thing that's known is that 0:26:38.200 --> 0:26:41.199 when you get damage to the hippocampus, that seems to 0:26:41.920 --> 0:26:46.840 mess up all of the spatial coherence of a recalled 0:26:47.040 --> 0:26:52.440 or imagined scene. So patients with hippocampal damage they can't 0:26:52.520 --> 0:26:58.479 picture a specific place or detailed surrounding events. Here's one 0:26:58.520 --> 0:26:59.400 way to think about this. 0:27:00.000 --> 0:27:04.560 When you move in a virtual reality world, the goggles 0:27:04.680 --> 0:27:08.920 keep track of where you are and all the objects 0:27:08.960 --> 0:27:11.560 and how things change when you move. 0:27:12.080 --> 0:27:14.200 And this is similar to what's going on in the brain. 0:27:14.280 --> 0:27:18.760 You have special cells in the hippocampus called place cells, 0:27:19.280 --> 0:27:23.320 which help to translate everything into a framework where you 0:27:23.359 --> 0:27:26.359 are at the center of it. And the idea is 0:27:26.400 --> 0:27:31.640 that these cells are critical to your imagination of scenes. 0:27:31.880 --> 0:27:37.240 So as you virtually move through your imagined scene, the 0:27:37.320 --> 0:27:43.280