1 00:00:05,280 --> 00:00:09,960 Speaker 1: Why does Arnold Schwarzenegger have an accent but Milakunis doesn't. 2 00:00:10,480 --> 00:00:13,920 Speaker 1: And why is there a correlation between how tall a 3 00:00:14,000 --> 00:00:17,479 Speaker 1: person is and how much his salary is likely to 4 00:00:17,520 --> 00:00:20,920 Speaker 1: be Why does an elderly person have a hard time 5 00:00:21,120 --> 00:00:24,439 Speaker 1: learning a new language but no trouble learning the name 6 00:00:24,520 --> 00:00:27,400 Speaker 1: and face of a new movie star. What would we 7 00:00:27,600 --> 00:00:30,960 Speaker 1: mean by saying that you are born as many people 8 00:00:31,600 --> 00:00:38,839 Speaker 1: but die as a single one. Welcome to the inner 9 00:00:39,000 --> 00:00:42,320 Speaker 1: cosmos with me, David Eagleman. I'm a neuroscientist and author 10 00:00:42,360 --> 00:00:46,920 Speaker 1: at Stanford, and in these episodes we sail deeply into 11 00:00:46,960 --> 00:00:51,319 Speaker 1: our three pound universe to understand why and how our 12 00:00:51,440 --> 00:01:02,440 Speaker 1: lives look the way they do. Today's episode is about 13 00:01:02,920 --> 00:01:06,480 Speaker 1: brain plasticity, which is the ability of the brain to 14 00:01:06,520 --> 00:01:12,480 Speaker 1: modify itself and how this changes throughout your lifetime. So 15 00:01:12,520 --> 00:01:16,000 Speaker 1: we're going to address why it is harder to teach 16 00:01:16,080 --> 00:01:19,880 Speaker 1: an old dog new tricks and ask whether that is 17 00:01:19,920 --> 00:01:26,480 Speaker 1: always true. So let's start fifty years ago. There was 18 00:01:26,560 --> 00:01:31,280 Speaker 1: a psychologist named Hans Lucas Touber at Mit and he 19 00:01:31,360 --> 00:01:36,160 Speaker 1: got curious about what had happened to soldiers who had 20 00:01:36,200 --> 00:01:40,320 Speaker 1: sustained head injuries in World War two. Now, this was 21 00:01:40,360 --> 00:01:43,319 Speaker 1: in the nineteen seventies, so the war had been almost 22 00:01:43,400 --> 00:01:47,560 Speaker 1: thirty years earlier. So he tracked down five hundred and 23 00:01:47,640 --> 00:01:51,640 Speaker 1: twenty men who had sustained brain damage during the battles, 24 00:01:52,200 --> 00:01:56,080 Speaker 1: and some had fared well in their recovery, but others 25 00:01:56,560 --> 00:01:59,720 Speaker 1: didn't have such good outcomes, and Toyber wanted to understand 26 00:01:59,760 --> 00:02:03,600 Speaker 1: what the difference was. So he scoured all the records 27 00:02:03,960 --> 00:02:06,840 Speaker 1: and he looked for the things that correlated with good 28 00:02:06,880 --> 00:02:09,760 Speaker 1: outcomes and bad outcomes. And you know what he found. 29 00:02:10,400 --> 00:02:14,760 Speaker 1: The younger the soldier was when he got the head injury, 30 00:02:14,919 --> 00:02:17,799 Speaker 1: the better he was now. And the older the soldier, 31 00:02:18,320 --> 00:02:23,840 Speaker 1: the more permanent the damage. Why it's because younger brains 32 00:02:23,960 --> 00:02:28,920 Speaker 1: are more flexible. There's more brain plasticity, which means the 33 00:02:28,960 --> 00:02:33,760 Speaker 1: ability of the circuitry to reconfigure itself, and so if 34 00:02:33,760 --> 00:02:37,480 Speaker 1: there's damage, a young brain can do what it needs 35 00:02:37,520 --> 00:02:41,760 Speaker 1: to to rewrite its circuitry and get itself back on track. 36 00:02:42,400 --> 00:02:45,920 Speaker 1: Now you know that I love analogies, So here's Today's 37 00:02:46,880 --> 00:02:50,560 Speaker 1: brains are like a map of Europe where you look 38 00:02:50,680 --> 00:02:55,400 Speaker 1: at the borders between the countries. So think of a 39 00:02:55,440 --> 00:02:59,240 Speaker 1: young brain like Europe five thousand years ago, and if 40 00:02:59,280 --> 00:03:03,560 Speaker 1: you can imagine different historical trajectories that could have happened, 41 00:03:04,080 --> 00:03:07,960 Speaker 1: the borders could have evolved in many ways. There's nothing 42 00:03:08,320 --> 00:03:12,520 Speaker 1: fundamental about where the borders between the countries sit today, 43 00:03:13,639 --> 00:03:19,200 Speaker 1: But today, after millennia of human history, the maps are 44 00:03:19,240 --> 00:03:23,240 Speaker 1: more settled into place. Now that humans have had centuries 45 00:03:23,320 --> 00:03:28,720 Speaker 1: to clang swords and discharge rifles, you get these territory 46 00:03:28,840 --> 00:03:32,400 Speaker 1: borders that are kind of stubborn to change. So think 47 00:03:32,440 --> 00:03:37,440 Speaker 1: of the borders between France and Italy and Switzerland. These 48 00:03:37,440 --> 00:03:41,360 Speaker 1: are totally arbitrary lines, but they're not likely to change 49 00:03:41,400 --> 00:03:47,200 Speaker 1: now because you don't have roving bands of marauders anymore 50 00:03:47,400 --> 00:03:51,920 Speaker 1: or bearded conquerors leading big horse armies. These things have 51 00:03:51,960 --> 00:03:57,160 Speaker 1: been replaced with the United Nations and international rules of engagement, 52 00:03:57,840 --> 00:04:02,520 Speaker 1: and economies have gotten increased seemly dependent on information and 53 00:04:02,600 --> 00:04:07,440 Speaker 1: expertise rather than on treasures that you can go pillage. 54 00:04:08,200 --> 00:04:13,760 Speaker 1: So even in the face of trade arguments and immigration debates, 55 00:04:14,080 --> 00:04:18,320 Speaker 1: the boundaries between European countries are really hard to move. 56 00:04:19,040 --> 00:04:22,920 Speaker 1: For the most part, the nations have settled into place, 57 00:04:23,640 --> 00:04:27,960 Speaker 1: so the land mass began with lots of possibilities for 58 00:04:28,080 --> 00:04:32,919 Speaker 1: where the borders sat essentially infinite possibility, but with time 59 00:04:33,560 --> 00:04:39,640 Speaker 1: the potential has narrowed, the map solidified into place, and 60 00:04:39,720 --> 00:04:43,400 Speaker 1: now it's not so easy to make big changes. The 61 00:04:43,520 --> 00:04:50,520 Speaker 1: brain matures like Europe through years of border disputes within 62 00:04:50,600 --> 00:04:57,680 Speaker 1: neural networks, the maps become increasingly solidified. So as a result, 63 00:04:58,279 --> 00:05:02,240 Speaker 1: brain injury is really dangerous for the elderly, but it's 64 00:05:02,360 --> 00:05:06,760 Speaker 1: less dangerous for the young because an older brain can't 65 00:05:06,800 --> 00:05:12,880 Speaker 1: easily reassign settled territories for new tasks. But a brain 66 00:05:12,960 --> 00:05:17,000 Speaker 1: that's at the dawn of its wars can still reimagine 67 00:05:17,040 --> 00:05:23,000 Speaker 1: its maps. Okay, so think about the trajectory of a 68 00:05:23,120 --> 00:05:28,320 Speaker 1: human life. So imagine a young baby born somewhere sometime. 69 00:05:28,800 --> 00:05:34,760 Speaker 1: When she's first born. Her brain has unbelievable flexibility wherever 70 00:05:35,000 --> 00:05:39,080 Speaker 1: and whenever she drops out of the womb. She will 71 00:05:39,200 --> 00:05:42,440 Speaker 1: soak up the local language. She'll pick up on the 72 00:05:42,480 --> 00:05:45,240 Speaker 1: subtle details of her culture and what to wear and 73 00:05:45,279 --> 00:05:49,919 Speaker 1: how to act. She will absorb the local religious beliefs. 74 00:05:50,000 --> 00:05:53,279 Speaker 1: She'll learn all of the rules around her. She'll learn 75 00:05:53,600 --> 00:05:58,200 Speaker 1: how to gather massive amounts of information, and depending on 76 00:05:58,640 --> 00:06:03,919 Speaker 1: her generation, that might be by unrolling a scroll or 77 00:06:03,920 --> 00:06:06,880 Speaker 1: flipping through the pages of a book or swiping the 78 00:06:07,000 --> 00:06:12,680 Speaker 1: screen of a small rectangle. But by the time she's grown, 79 00:06:13,680 --> 00:06:18,760 Speaker 1: that story of flexibility has changed somewhat. Her brain isn't 80 00:06:18,800 --> 00:06:23,480 Speaker 1: so flexible now. She belongs to a particular political party, 81 00:06:24,080 --> 00:06:28,640 Speaker 1: and she's unlikely to change. She plays the piano reasonably well, 82 00:06:28,960 --> 00:06:32,400 Speaker 1: but she doesn't have any particular interest in studying violin 83 00:06:32,560 --> 00:06:35,640 Speaker 1: or other instruments. She likes to cook, and all of 84 00:06:35,680 --> 00:06:40,200 Speaker 1: her dishes exploit combinations of the fourteen ingredients that she 85 00:06:40,320 --> 00:06:44,280 Speaker 1: is used to. She spends her online time with a 86 00:06:44,440 --> 00:06:48,719 Speaker 1: vanishingly small fraction of the billions of available web pages. 87 00:06:49,680 --> 00:06:53,039 Speaker 1: She has a respectable golf game, but she doesn't have 88 00:06:53,080 --> 00:06:57,040 Speaker 1: any curiosity about other sports. She lives in a city 89 00:06:57,040 --> 00:07:00,479 Speaker 1: of eight million people, but she only has three close friends. 90 00:07:01,120 --> 00:07:03,880 Speaker 1: She isn't particularly interested in the science that she didn't 91 00:07:03,920 --> 00:07:07,400 Speaker 1: already learn in school. When she goes to the store, 92 00:07:07,680 --> 00:07:11,480 Speaker 1: she passes racks of shirts until she finds the kind 93 00:07:11,600 --> 00:07:14,440 Speaker 1: that she always wears, and she selects two of them 94 00:07:14,480 --> 00:07:18,960 Speaker 1: in her standard colors. Her haircut is the same as 95 00:07:18,960 --> 00:07:22,360 Speaker 1: it was since she was a teenager. Okay, so this 96 00:07:22,400 --> 00:07:26,920 Speaker 1: sort of life trajectory underscores a general point, and we've 97 00:07:26,920 --> 00:07:30,440 Speaker 1: all seen this before, which is that babies are born 98 00:07:30,800 --> 00:07:33,120 Speaker 1: with not many built in skills, and they have a 99 00:07:33,240 --> 00:07:38,120 Speaker 1: ton of plasticity. They can learn anything, while adults have 100 00:07:38,400 --> 00:07:43,560 Speaker 1: mastered specific tasks, but at the expense of flexibility. So 101 00:07:43,640 --> 00:07:50,120 Speaker 1: there's a trade off between adaptability and efficiency. So as 102 00:07:50,160 --> 00:07:54,280 Speaker 1: your brain gets good at certain jobs, it becomes less 103 00:07:54,400 --> 00:07:58,800 Speaker 1: able to tackle others. Now, just to be clear, this 104 00:07:58,880 --> 00:08:02,320 Speaker 1: is not to say that adam dults aren't intelligent. In fact, 105 00:08:02,400 --> 00:08:05,360 Speaker 1: it's just the opposite. An adult can do all kinds 106 00:08:05,400 --> 00:08:07,840 Speaker 1: of things that a baby can't. An adult can run 107 00:08:07,880 --> 00:08:11,320 Speaker 1: a company, or fix an air conditioner, or plan a 108 00:08:11,360 --> 00:08:17,720 Speaker 1: business takeover precisely because the adult's brain understands things about 109 00:08:17,720 --> 00:08:21,320 Speaker 1: the functioning of the world that a child's brain just 110 00:08:21,600 --> 00:08:25,480 Speaker 1: can't understand. So the way we capture this concept is 111 00:08:25,520 --> 00:08:30,560 Speaker 1: to say that the baby's brain has fluid intelligence, meaning 112 00:08:30,560 --> 00:08:36,880 Speaker 1: they can learn anything, while adult brains have crystallized intelligence. So, 113 00:08:37,040 --> 00:08:40,920 Speaker 1: for example, a few episodes ago, I mentioned a story 114 00:08:41,000 --> 00:08:45,560 Speaker 1: about the violinist Yittsawk Pearlman, in which a fan told 115 00:08:45,679 --> 00:08:48,360 Speaker 1: him that he would give his life to play like that, 116 00:08:48,559 --> 00:08:53,400 Speaker 1: and Pearlman said, I did what Pearlman was pointing to 117 00:08:53,559 --> 00:08:56,360 Speaker 1: is a fact of life. To get good at one 118 00:08:56,400 --> 00:09:00,200 Speaker 1: thing is to close the door on other things. So 119 00:09:00,640 --> 00:09:04,400 Speaker 1: Pearlman went from presumably being able to tackle any instrument 120 00:09:04,760 --> 00:09:09,439 Speaker 1: to being superlative at one at the expense of everything else. 121 00:09:09,520 --> 00:09:14,479 Speaker 1: It's unlikely that Pearlman could also be a professional baseball 122 00:09:14,520 --> 00:09:18,280 Speaker 1: player in the same lifetime. Why because you have only 123 00:09:18,320 --> 00:09:22,680 Speaker 1: one single life, and what you devote yourself to sends 124 00:09:22,720 --> 00:09:26,760 Speaker 1: you down particular roads. But that means that all the 125 00:09:26,960 --> 00:09:33,040 Speaker 1: other roads will forever remain untrodden by you. And this 126 00:09:33,160 --> 00:09:37,360 Speaker 1: is what the philosopher Martin Heidegger was pointing to when 127 00:09:37,440 --> 00:09:42,080 Speaker 1: he said, quote every man is born as many men 128 00:09:42,679 --> 00:09:47,280 Speaker 1: and dies as a single one end quote. You're born 129 00:09:47,600 --> 00:09:50,800 Speaker 1: with lots of possibility, but when you die, you are 130 00:09:51,080 --> 00:09:55,959 Speaker 1: just the limited you. Now, from the point of view 131 00:09:56,040 --> 00:09:59,680 Speaker 1: of your neural networks, what does it mean to descend 132 00:09:59,720 --> 00:10:04,040 Speaker 1: into pattern and habit? So here's another analogy to help 133 00:10:04,120 --> 00:10:08,800 Speaker 1: us picture this. Imagine two villages a few miles apart. 134 00:10:09,320 --> 00:10:13,080 Speaker 1: So people interested in going from one settlement over to 135 00:10:13,080 --> 00:10:17,640 Speaker 1: the other one, they take all possible paths. Some travelers 136 00:10:18,160 --> 00:10:22,600 Speaker 1: walk the scenic route along the ridgetops, but others prefer 137 00:10:22,679 --> 00:10:26,600 Speaker 1: the shade of the cliff side, and some people move 138 00:10:26,640 --> 00:10:30,360 Speaker 1: among the slippery rocks by the river, and others take 139 00:10:30,400 --> 00:10:35,200 Speaker 1: the riskier but faster route through the woods. Okay, with 140 00:10:35,400 --> 00:10:41,520 Speaker 1: time and experience, one route ends up proving more popular. 141 00:10:41,559 --> 00:10:45,280 Speaker 1: Maybe it makes better sense or it's faster. But eventually 142 00:10:45,440 --> 00:10:50,120 Speaker 1: that path becomes grooved where the most people have walked, 143 00:10:50,440 --> 00:10:55,959 Speaker 1: and it starts to become the standard. After some years 144 00:10:55,960 --> 00:11:00,280 Speaker 1: go by, the local government lays down roadways, and after 145 00:11:00,280 --> 00:11:04,320 Speaker 1: a few decades that expands into highways, and now the 146 00:11:04,360 --> 00:11:08,400 Speaker 1: way to get from here to there is really nailed down. 147 00:11:09,400 --> 00:11:14,679 Speaker 1: So you started with broad optionality, but eventually that gets 148 00:11:14,720 --> 00:11:19,320 Speaker 1: reduced to the standard path. And this is what happens 149 00:11:19,760 --> 00:11:25,520 Speaker 1: inside brains. They begin with almost infinite possible routes through 150 00:11:25,640 --> 00:11:32,199 Speaker 1: the neural networks, but with time the practiced pathways become 151 00:11:32,280 --> 00:11:39,000 Speaker 1: difficult to exit, the unused paths become thinned away. So 152 00:11:39,160 --> 00:11:43,600 Speaker 1: through decades of experience, the brain comes to physically represent 153 00:11:44,320 --> 00:11:50,960 Speaker 1: your world, and your decisions follow the remaining hard paved paths. 154 00:11:51,920 --> 00:11:53,480 Speaker 1: I mean, just think about what it would be like 155 00:11:53,600 --> 00:11:56,360 Speaker 1: if you were born with your genes and your brain 156 00:11:56,920 --> 00:12:00,640 Speaker 1: in a different part of the world. Maybe a different 157 00:12:00,679 --> 00:12:03,840 Speaker 1: generation a thousand years ago or maybe a thousand years 158 00:12:03,880 --> 00:12:08,360 Speaker 1: from now. You would function and thrive in whatever environment 159 00:12:08,400 --> 00:12:12,119 Speaker 1: you drop into, but you'd speak a totally different language, 160 00:12:12,559 --> 00:12:16,360 Speaker 1: you'd have a different religion, you would believe different things 161 00:12:16,440 --> 00:12:20,520 Speaker 1: about the world. But as it happens to have turned out, 162 00:12:20,559 --> 00:12:22,880 Speaker 1: you were born in your hometown, and you grew up 163 00:12:22,960 --> 00:12:26,920 Speaker 1: with your language and your parents, and so all of 164 00:12:26,960 --> 00:12:32,680 Speaker 1: the us that could have been ended up getting thinned away. 165 00:12:34,040 --> 00:12:38,720 Speaker 1: Now that might sound sad to lose the optionality, but 166 00:12:38,840 --> 00:12:43,959 Speaker 1: the upside of a solidifying brain is that you end 167 00:12:44,080 --> 00:12:49,440 Speaker 1: up with lightning fast ways of solving problems. Now, the 168 00:12:49,480 --> 00:12:54,040 Speaker 1: downside is that it's harder to attack new problems with wild, 169 00:12:54,280 --> 00:12:59,560 Speaker 1: unstructured inventiveness. Now, from the neuroscience point of view, there's 170 00:12:59,600 --> 00:13:04,000 Speaker 1: also a second reason why older brains are less flexible, 171 00:13:04,040 --> 00:13:08,240 Speaker 1: and this is beyond the diminishing optionality in the pathways issue. 172 00:13:08,640 --> 00:13:12,800 Speaker 1: When older brains make changes, they do so only in 173 00:13:12,920 --> 00:13:21,000 Speaker 1: small spots. In contrast, baby's brains modify across vast territories, 174 00:13:21,559 --> 00:13:24,160 Speaker 1: and this is because of chemicals in the brain called 175 00:13:24,160 --> 00:13:29,560 Speaker 1: neurotransmitters that are broadcast broadly in a baby's brain, So 176 00:13:30,360 --> 00:13:35,520 Speaker 1: in an infant brain, these chemicals like acetylcholine. They transmit 177 00:13:35,679 --> 00:13:39,480 Speaker 1: announcements throughout the brain, saying, Hey, something important just happen, 178 00:13:40,000 --> 00:13:44,680 Speaker 1: And this allows pathways and connections to change and modify. 179 00:13:45,160 --> 00:13:50,560 Speaker 1: So a baby's brain is changeable throughout its territory, and 180 00:13:50,720 --> 00:13:55,040 Speaker 1: over years its understanding of the world comes into focus 181 00:13:55,120 --> 00:14:00,520 Speaker 1: like a polaroid photograph. But an adult brain changes only 182 00:14:00,600 --> 00:14:03,200 Speaker 1: little bits at a time. It keeps most of its 183 00:14:03,240 --> 00:14:07,560 Speaker 1: connections locked into place to hold on to what has 184 00:14:07,679 --> 00:14:12,760 Speaker 1: been learned, and only small areas are made flexible via 185 00:14:12,880 --> 00:14:17,360 Speaker 1: a combination lock of the right neurotransmitters. So an adult 186 00:14:17,440 --> 00:14:22,120 Speaker 1: brain is like a point to list artist who modifies 187 00:14:22,240 --> 00:14:25,920 Speaker 1: the color of only a few dots in an almost 188 00:14:26,120 --> 00:14:31,320 Speaker 1: finished painting. Now you might wonder what does it feel 189 00:14:31,360 --> 00:14:36,160 Speaker 1: like to be inside the massively flexible brain of a baby. 190 00:14:36,360 --> 00:14:39,080 Speaker 1: I mean, we were all there as infants, but we 191 00:14:39,160 --> 00:14:42,360 Speaker 1: can't remember that. So what is it like to be 192 00:14:42,440 --> 00:14:48,280 Speaker 1: so plastic, so uninhibited and learning about a wide range 193 00:14:48,320 --> 00:14:52,040 Speaker 1: of novel events. Well, you can probably get close to 194 00:14:52,200 --> 00:14:57,800 Speaker 1: understanding it by considering other situations in your life in 195 00:14:57,840 --> 00:15:03,680 Speaker 1: which your awareness plasticity are firing on all cylinders. So 196 00:15:04,000 --> 00:15:07,680 Speaker 1: when you are traveling in a new land. You drink 197 00:15:07,720 --> 00:15:11,160 Speaker 1: in all the sights and sounds and smells of the 198 00:15:11,280 --> 00:15:17,720 Speaker 1: foreign country. You are experiencing lots of novelty and more 199 00:15:17,960 --> 00:15:24,200 Speaker 1: learning and more distributed attention. After all, at home, you 200 00:15:24,240 --> 00:15:27,000 Speaker 1: don't pay much attention to much of anything going on. 201 00:15:27,280 --> 00:15:30,760 Speaker 1: Why because it's predictable. You know what to expect there. 202 00:15:31,280 --> 00:15:35,600 Speaker 1: But when you're the traveler, you overflow with attention and 203 00:15:35,640 --> 00:15:40,040 Speaker 1: your brain is changing much more. So think about it 204 00:15:40,080 --> 00:15:43,560 Speaker 1: like this. When you are highly engaged and paying attention, 205 00:15:44,080 --> 00:15:48,480 Speaker 1: you are like a baby again. So the difference is 206 00:15:48,560 --> 00:15:53,480 Speaker 1: between a baby's very fluid brain and an adult's crystallized brain. 207 00:15:53,560 --> 00:15:56,760 Speaker 1: This is easy to into it, but the neural transition 208 00:15:57,440 --> 00:16:03,560 Speaker 1: from one to the other does happened in a smooth line. Instead, 209 00:16:03,960 --> 00:16:08,200 Speaker 1: it's like a door that swings closed and once it shuts, 210 00:16:09,080 --> 00:16:12,800 Speaker 1: large scale change is over. And this is the concept 211 00:16:13,200 --> 00:16:17,600 Speaker 1: of this sensitive period. So to understand the sensitive period, 212 00:16:18,200 --> 00:16:22,640 Speaker 1: consider an infant named Matthew, who is from my hometown. 213 00:16:23,040 --> 00:16:27,280 Speaker 1: He started having epileptic seizures as a very young boy, 214 00:16:27,320 --> 00:16:30,480 Speaker 1: and by the time he was six, these seizures were 215 00:16:30,520 --> 00:16:35,800 Speaker 1: happening with increasing frequency, so he could be having multiple 216 00:16:35,880 --> 00:16:39,720 Speaker 1: seizures in an hour, and his parents tried everything they 217 00:16:39,760 --> 00:16:41,760 Speaker 1: could do to figure out what is going on here, 218 00:16:41,760 --> 00:16:44,480 Speaker 1: and they finally found out that he had something called 219 00:16:44,960 --> 00:16:50,000 Speaker 1: Rasmussen's encephalitis, which is an inflammation that affects an entire 220 00:16:50,280 --> 00:16:53,960 Speaker 1: half of his brain. And so they searched everywhere for 221 00:16:54,000 --> 00:16:57,080 Speaker 1: a solution, and they came to find out that really 222 00:16:57,160 --> 00:17:03,800 Speaker 1: the only solution is a radical neurosurgery called a hemispherectomy. 223 00:17:03,880 --> 00:17:08,119 Speaker 1: And in this surgery, an entire half of the brain 224 00:17:08,520 --> 00:17:12,600 Speaker 1: is removed, just taken out, and that empty half of 225 00:17:12,640 --> 00:17:16,240 Speaker 1: the skull fills up with cerebra spinal fluid, and if 226 00:17:16,240 --> 00:17:19,640 Speaker 1: you do brain imaging, what you see is just blackness 227 00:17:19,720 --> 00:17:23,080 Speaker 1: in that half of the head. Now, this is a 228 00:17:23,160 --> 00:17:26,000 Speaker 1: horrifying thing for a parent to put their child through. 229 00:17:26,280 --> 00:17:29,840 Speaker 1: But the completely amazing thing is that kids who get 230 00:17:29,840 --> 00:17:34,360 Speaker 1: the surgery generally turn out to be just fine. They 231 00:17:34,400 --> 00:17:37,480 Speaker 1: sometimes have a slight limp on the other side of 232 00:17:37,520 --> 00:17:39,760 Speaker 1: their body because the left side of the body is 233 00:17:39,800 --> 00:17:42,280 Speaker 1: controlled by the right side of the brain and vice versa, 234 00:17:42,400 --> 00:17:45,240 Speaker 1: but other than that, they don't have any particular signs 235 00:17:45,280 --> 00:17:48,600 Speaker 1: that tell anyone that they only have half of their 236 00:17:48,640 --> 00:18:07,920 Speaker 1: brain remaining. Now I'm going to talk more about hemispherectomy 237 00:18:08,000 --> 00:18:09,760 Speaker 1: is in a future episode. But the thing I want 238 00:18:09,760 --> 00:18:13,600 Speaker 1: to emphasize here is that this kind of surgery is 239 00:18:13,960 --> 00:18:17,520 Speaker 1: recommended only if the patient is less than let's say 240 00:18:17,600 --> 00:18:20,960 Speaker 1: eight years old. Matthew was six when he went under 241 00:18:21,000 --> 00:18:24,160 Speaker 1: the knife, which is nearing old age for this surgery. 242 00:18:24,480 --> 00:18:28,159 Speaker 1: If a child is older, let's say an adolescent, he 243 00:18:28,240 --> 00:18:31,720 Speaker 1: will have to function in life by bending tasks to 244 00:18:31,800 --> 00:18:35,320 Speaker 1: fit what his brain can do, rather than counting on 245 00:18:35,400 --> 00:18:39,960 Speaker 1: his brain to adapt to the tasks. So the thing 246 00:18:40,040 --> 00:18:42,600 Speaker 1: to note here is that there is a door that 247 00:18:42,720 --> 00:18:46,320 Speaker 1: closes at about eight years old, where your brain before 248 00:18:46,359 --> 00:18:49,040 Speaker 1: that is so flexible that even if it only has 249 00:18:49,560 --> 00:18:53,600 Speaker 1: half the real estate available, it can readjust to take 250 00:18:53,640 --> 00:18:57,280 Speaker 1: care of all the functions that it needs. Before eight, 251 00:18:57,359 --> 00:19:02,680 Speaker 1: you're fine. After probably not so fine now. This kind 252 00:19:02,680 --> 00:19:06,200 Speaker 1: of age limit. This is seen in so many aspects 253 00:19:06,240 --> 00:19:11,240 Speaker 1: of brain function. For example, sometimes there are heartbreaking cases 254 00:19:11,359 --> 00:19:15,359 Speaker 1: in which a child is so profoundly neglected through her 255 00:19:15,480 --> 00:19:20,280 Speaker 1: childhood without conversation and affection that she will end up 256 00:19:20,520 --> 00:19:25,040 Speaker 1: incapable of speech. And if that child is found after 257 00:19:25,240 --> 00:19:28,359 Speaker 1: a certain age, let's say about seven, she will be 258 00:19:28,680 --> 00:19:33,240 Speaker 1: incapable of ever learning speech. Even when a team of 259 00:19:33,320 --> 00:19:37,399 Speaker 1: psychologists come in and work with her for years to 260 00:19:37,560 --> 00:19:41,160 Speaker 1: try to teach her language, it's too late. I told 261 00:19:41,200 --> 00:19:44,480 Speaker 1: the story of one such girl, Danielle, in my book 262 00:19:44,520 --> 00:19:47,280 Speaker 1: Live Wired, and I'll return to her story in a 263 00:19:47,359 --> 00:19:49,520 Speaker 1: future episode. But the thing I want to emphasize for 264 00:19:49,600 --> 00:19:54,320 Speaker 1: today is that the door for learning language closes. And 265 00:19:54,359 --> 00:19:57,320 Speaker 1: I'm not talking about learning a second language or dealing 266 00:19:57,359 --> 00:19:59,439 Speaker 1: with an accent or something like that. I'm talking about 267 00:19:59,640 --> 00:20:04,560 Speaker 1: the idea of language. What language is, as in, how 268 00:20:04,600 --> 00:20:07,919 Speaker 1: do I put words together to label things in the 269 00:20:07,920 --> 00:20:11,800 Speaker 1: outside world and communicate with someone else this way, with 270 00:20:11,880 --> 00:20:16,680 Speaker 1: a particular grammar and sentence structure and so on. If 271 00:20:16,720 --> 00:20:21,000 Speaker 1: a child does not get language in the formative years, 272 00:20:21,600 --> 00:20:28,800 Speaker 1: it becomes too late. Her maps have largely stabilized into 273 00:20:29,000 --> 00:20:33,159 Speaker 1: place and they can't be changed anymore. So children like 274 00:20:33,560 --> 00:20:36,840 Speaker 1: Matthew who got a hemisphectomy, or a child like Danielle 275 00:20:36,920 --> 00:20:40,320 Speaker 1: who didn't get language in time, they tell the same story, 276 00:20:40,359 --> 00:20:43,920 Speaker 1: which is that brains are really flexible at the beginning 277 00:20:44,400 --> 00:20:47,280 Speaker 1: in this window of time known as the sensitive period, 278 00:20:47,720 --> 00:20:52,480 Speaker 1: and as this period passes, the neural geography becomes more 279 00:20:52,600 --> 00:20:57,879 Speaker 1: difficult to change. So as seen with children like Danielle, 280 00:20:58,119 --> 00:21:03,080 Speaker 1: a young child's brain needs to hear lots of language 281 00:21:03,160 --> 00:21:07,240 Speaker 1: during the sensitive period, and without that input, the neurons 282 00:21:07,320 --> 00:21:12,600 Speaker 1: don't arrange themselves to capture the fundamental concepts of language. 283 00:21:13,359 --> 00:21:14,880 Speaker 1: And by the way, it's a side note, you might 284 00:21:14,920 --> 00:21:18,879 Speaker 1: wonder what happens with a deaf baby who doesn't hear 285 00:21:19,240 --> 00:21:23,320 Speaker 1: any auditory input, and the answer is, as long as 286 00:21:23,359 --> 00:21:27,280 Speaker 1: the parents present sign language to the baby, her brain 287 00:21:27,320 --> 00:21:32,040 Speaker 1: will wire up correctly for communication. The deaf baby will 288 00:21:32,320 --> 00:21:38,080 Speaker 1: employ her hands to babble, making resemblances to sign language, 289 00:21:38,080 --> 00:21:40,399 Speaker 1: and the same way that a hearing baby exposed to 290 00:21:40,480 --> 00:21:44,199 Speaker 1: language will babble with her vocal cords. If there is 291 00:21:44,400 --> 00:21:47,040 Speaker 1: input to pick up on, the baby will do so. 292 00:21:47,880 --> 00:21:51,560 Speaker 1: As long as that input arrives within the sensitive period. 293 00:21:51,960 --> 00:21:55,840 Speaker 1: After that door swing shut, it's too late to learn 294 00:21:55,880 --> 00:22:01,720 Speaker 1: the fundamentals of communication. So there's a window for acquiring 295 00:22:01,800 --> 00:22:05,119 Speaker 1: the ability to communicate, and there are also windows for 296 00:22:05,320 --> 00:22:10,239 Speaker 1: more subtle aspects of language, like accents. So take the 297 00:22:10,320 --> 00:22:15,480 Speaker 1: actress Mila Kunis. She speaks American English with no discernible accent, 298 00:22:16,200 --> 00:22:18,600 Speaker 1: so you probably didn't know that she was born in 299 00:22:18,800 --> 00:22:22,480 Speaker 1: Ukraine and lived there, not speaking a word of English 300 00:22:22,600 --> 00:22:27,280 Speaker 1: until the age of seven. Now, in contrast, Arnold Schwarzenegger, 301 00:22:27,640 --> 00:22:31,399 Speaker 1: who's been in American filmmaking since his early twenties, he 302 00:22:31,480 --> 00:22:35,240 Speaker 1: has a very strong Austrian accent. Why because he didn't 303 00:22:35,280 --> 00:22:37,719 Speaker 1: move to America until he was twenty one, and that 304 00:22:37,920 --> 00:22:43,600 Speaker 1: meant his use of English began too late. Brain wise, generally, 305 00:22:44,200 --> 00:22:47,040 Speaker 1: if you arrive in a new country during your first 306 00:22:47,080 --> 00:22:51,000 Speaker 1: seven years, your fluency in the new tongue will be 307 00:22:51,040 --> 00:22:54,199 Speaker 1: as high as a native speakers, because your window of 308 00:22:54,240 --> 00:22:59,159 Speaker 1: sensitivity for obtaining the sounds that's still open. If you 309 00:22:59,480 --> 00:23:02,280 Speaker 1: immigrate when you're eight to ten years old, you have 310 00:23:02,320 --> 00:23:05,639 Speaker 1: a slightly more difficult time blending in, but you'll be close. 311 00:23:06,080 --> 00:23:09,399 Speaker 1: If you're past your teen years. When you move like 312 00:23:09,600 --> 00:23:13,479 Speaker 1: Arnold was, your fluency is likely to remain low, and 313 00:23:13,480 --> 00:23:17,240 Speaker 1: you're going to have an accent that reveals your history. 314 00:23:17,560 --> 00:23:21,920 Speaker 1: So your ability to sonically morph into a different culture 315 00:23:22,640 --> 00:23:25,880 Speaker 1: is a door that remains open for only about a decade. 316 00:23:27,000 --> 00:23:29,960 Speaker 1: And let's take another example. Take something like vision. So 317 00:23:30,400 --> 00:23:35,160 Speaker 1: imagine a child is born with misaligned eyes where one 318 00:23:35,200 --> 00:23:38,800 Speaker 1: eye is pointing straight but the other eye points inwarder outward. 319 00:23:38,840 --> 00:23:42,520 Speaker 1: This is known as strabismus, and colloquially it's often called 320 00:23:42,840 --> 00:23:46,040 Speaker 1: being cross eyed or walleyed. What you do clinically is 321 00:23:46,080 --> 00:23:49,440 Speaker 1: you fix the extra ocular muscles so the eyes can 322 00:23:49,520 --> 00:23:53,160 Speaker 1: point the same direction, and then you cover the good 323 00:23:53,200 --> 00:23:56,000 Speaker 1: eye for a while, which allows the weak eye to 324 00:23:56,600 --> 00:24:00,600 Speaker 1: fight to regain its lost territory. But no out that 325 00:24:00,680 --> 00:24:03,000 Speaker 1: the good eye has to be patched. You have to 326 00:24:03,080 --> 00:24:07,160 Speaker 1: do this technique within this sensitive period about the first 327 00:24:07,280 --> 00:24:11,520 Speaker 1: six years, otherwise it's too late. The vision will never 328 00:24:11,600 --> 00:24:16,280 Speaker 1: be recoverable after that from the weakey. After six years, 329 00:24:16,320 --> 00:24:19,800 Speaker 1: the dirt roads in the brain have been paved into 330 00:24:19,880 --> 00:24:24,760 Speaker 1: highways and you can't now modify them. So this influence 331 00:24:25,080 --> 00:24:28,879 Speaker 1: of developmental timing. You see this across all the senses. 332 00:24:29,680 --> 00:24:32,960 Speaker 1: I talked in earlier episodes about how the body maps 333 00:24:33,080 --> 00:24:37,560 Speaker 1: readjust if you have an amputation or when you learn 334 00:24:37,600 --> 00:24:41,920 Speaker 1: a new musical instrument, but across the board, these kinds 335 00:24:41,960 --> 00:24:46,080 Speaker 1: of changes happen more in young brains than in old brains, 336 00:24:47,160 --> 00:24:50,840 Speaker 1: just like Mila Kunis with her unaccented speech. So we 337 00:24:51,000 --> 00:24:54,199 Speaker 1: find that Jitzak Peerlman took up the violin at a 338 00:24:54,320 --> 00:24:56,840 Speaker 1: very young age. If you were to take up the 339 00:24:56,960 --> 00:25:00,600 Speaker 1: violin for the first time in your teenage years, there's 340 00:25:00,720 --> 00:25:04,720 Speaker 1: no possibility that you would ever become a pearlman. Even 341 00:25:04,760 --> 00:25:07,840 Speaker 1: if you worked really hard to rack up the same 342 00:25:07,920 --> 00:25:12,040 Speaker 1: number of hours of practice. Your brain is already behind 343 00:25:12,080 --> 00:25:16,000 Speaker 1: in the race. It has grown too solidified by the 344 00:25:16,040 --> 00:25:19,399 Speaker 1: time you start doing your first piscata as a teenager. 345 00:25:20,560 --> 00:25:25,840 Speaker 1: So acquiring vision and language and violin proficiency, this all 346 00:25:25,880 --> 00:25:29,680 Speaker 1: depends on input from the world, and if a severely 347 00:25:29,800 --> 00:25:34,880 Speaker 1: neglected child like Danielle doesn't receive this input, she can't 348 00:25:35,200 --> 00:25:39,280 Speaker 1: later the ability to learn language, to possess vision, to 349 00:25:39,840 --> 00:25:44,040 Speaker 1: interact socially, to walk normally, to have normal neurodevelopment. This 350 00:25:44,160 --> 00:25:47,600 Speaker 1: is all limited to the years of young childhood, and 351 00:25:47,680 --> 00:25:52,159 Speaker 1: after a certain point these abilities are lost. The brain 352 00:25:52,680 --> 00:25:56,400 Speaker 1: needs to experience the proper input within the right window 353 00:25:56,880 --> 00:26:02,320 Speaker 1: to achieve its most useful connectivity. Now, as a result 354 00:26:02,440 --> 00:26:06,840 Speaker 1: of this diminishing flexibility, we are highly influenced by the 355 00:26:06,880 --> 00:26:10,400 Speaker 1: events that happen in our childhoods. So here's a really 356 00:26:10,400 --> 00:26:15,560 Speaker 1: interesting example. Consider the correlation between how tall a man 357 00:26:15,840 --> 00:26:20,600 Speaker 1: is and how much salary he will command. In America, 358 00:26:21,000 --> 00:26:25,080 Speaker 1: each additional inch of height translates into a one point 359 00:26:25,119 --> 00:26:29,920 Speaker 1: eight percent increase in take home pay. Why is that well, 360 00:26:30,240 --> 00:26:34,199 Speaker 1: the popular assumption is that this stems from discrimination in 361 00:26:34,280 --> 00:26:38,040 Speaker 1: hiring practices. Everyone wants to hire the tall guy because 362 00:26:38,040 --> 00:26:41,200 Speaker 1: of his commanding presence. But it turns out there is 363 00:26:41,720 --> 00:26:46,600 Speaker 1: a deeper reason. The best indicator of a male's future 364 00:26:46,680 --> 00:26:52,479 Speaker 1: salary is how tall he was at the age of sixteen. However, 365 00:26:52,520 --> 00:26:55,800 Speaker 1: tall he grows after that doesn't change the outcome. Now, 366 00:26:55,800 --> 00:26:59,080 Speaker 1: how do we understand that? Could it be some effect 367 00:26:59,119 --> 00:27:03,920 Speaker 1: of nutritional differences between people? Know because when the researchers 368 00:27:04,000 --> 00:27:08,240 Speaker 1: correlated with height at ages seven or eleven, the effect 369 00:27:08,320 --> 00:27:13,160 Speaker 1: wasn't as strong. Instead, it's that the teenage years are 370 00:27:13,200 --> 00:27:17,439 Speaker 1: a time when social status is being worked out, and 371 00:27:17,520 --> 00:27:21,600 Speaker 1: as a result, who you are as an adult strongly 372 00:27:21,640 --> 00:27:26,119 Speaker 1: depends on who you were then. In fact, studies that 373 00:27:26,240 --> 00:27:31,320 Speaker 1: track thousands of children into adulthood find that socially oriented 374 00:27:31,359 --> 00:27:35,520 Speaker 1: careers like sales or managing other people show the strongest 375 00:27:35,560 --> 00:27:39,240 Speaker 1: effect of teenage height, and other careers like blue collar 376 00:27:39,280 --> 00:27:44,800 Speaker 1: work or artistic trades are less influenced. So how people 377 00:27:44,920 --> 00:27:49,680 Speaker 1: treat you during your formative years has an enormous impact. 378 00:27:49,800 --> 00:27:53,240 Speaker 1: On your comportment in the world in terms of self 379 00:27:53,320 --> 00:27:57,679 Speaker 1: esteem and confidence and leadership. Here's another example. Think about 380 00:27:58,200 --> 00:28:00,880 Speaker 1: Oprah Winfrey, who is worth the bid two point eight 381 00:28:01,000 --> 00:28:04,320 Speaker 1: billion dollars. So I was a little surprised when I 382 00:28:04,400 --> 00:28:08,440 Speaker 1: read that she has a deep rooted fear of ending 383 00:28:08,520 --> 00:28:12,840 Speaker 1: up homeless and penniless. But it's because of the path 384 00:28:13,119 --> 00:28:16,840 Speaker 1: that got her here. Before she was an empress of 385 00:28:16,880 --> 00:28:20,840 Speaker 1: the media, she was an impoverished child in Mississippi. She 386 00:28:20,920 --> 00:28:25,000 Speaker 1: was born to a teenage single mother. So who she 387 00:28:25,440 --> 00:28:30,879 Speaker 1: was then influenced who she is now. The Great Aristotle 388 00:28:31,119 --> 00:28:33,959 Speaker 1: noted this twenty four hundred years ago. He said, quote, 389 00:28:34,240 --> 00:28:38,960 Speaker 1: the habits we form from childhood make no small difference, 390 00:28:39,320 --> 00:28:44,840 Speaker 1: but rather they make all the difference. Okay, So to 391 00:28:45,000 --> 00:28:49,440 Speaker 1: capture the idea of the sensitive period, I introduced the 392 00:28:49,480 --> 00:28:52,800 Speaker 1: metaphor of a door swinging shut. But now we're ready 393 00:28:52,840 --> 00:28:55,800 Speaker 1: to take the analogy to the next level. It's not 394 00:28:56,360 --> 00:29:00,080 Speaker 1: one door, it's a bunch of different doors which swing 395 00:29:00,160 --> 00:29:04,360 Speaker 1: shut at different times. So let's look at an example 396 00:29:04,400 --> 00:29:07,440 Speaker 1: of that. Sometimes the brain is so impressionable in its 397 00:29:07,520 --> 00:29:10,120 Speaker 1: earliest days that it can sometimes get into hot water. 398 00:29:10,480 --> 00:29:15,680 Speaker 1: For example, the baby goose hatches from its egg, and 399 00:29:15,720 --> 00:29:20,960 Speaker 1: it establishes a parental relationship with the first animate object 400 00:29:21,040 --> 00:29:24,280 Speaker 1: that it sees. And this is a sufficient strategy in 401 00:29:24,320 --> 00:29:27,920 Speaker 1: most cases because that first sight is usually its mother. 402 00:29:28,040 --> 00:29:32,120 Speaker 1: But it can get fooled in the wrong circumstances, and 403 00:29:32,160 --> 00:29:34,880 Speaker 1: this was shown in the nineteen thirties by the zoologist 404 00:29:35,160 --> 00:29:38,280 Speaker 1: Conrad Lorenz, who didn't have to work hard for the 405 00:29:38,280 --> 00:29:40,520 Speaker 1: geese to imprint on him. Instead, he just needed to 406 00:29:40,640 --> 00:29:44,320 Speaker 1: show up in the right window of plasticity right after 407 00:29:44,360 --> 00:29:47,400 Speaker 1: they hatched, and then they would imprint on him and 408 00:29:47,600 --> 00:29:51,200 Speaker 1: follow him around. So that's an example of a fast 409 00:29:51,240 --> 00:29:55,040 Speaker 1: swinging door for geese to imprint on their parent. But 410 00:29:55,680 --> 00:29:58,880 Speaker 1: the geese can still learn other things later in life, 411 00:29:59,160 --> 00:30:02,240 Speaker 1: such as where the is or where to best seek food, 412 00:30:02,720 --> 00:30:06,600 Speaker 1: or the identities of other geese that they meet in adulthood. 413 00:30:07,440 --> 00:30:12,440 Speaker 1: So sensitive periods are different for different tasks of the brain, 414 00:30:12,720 --> 00:30:16,600 Speaker 1: and not all brain regions are equally plastic in terms 415 00:30:16,600 --> 00:30:20,320 Speaker 1: of how flexibly they begin and how long they retain 416 00:30:20,520 --> 00:30:24,880 Speaker 1: their adaptability. So is there a pattern to which areas 417 00:30:25,160 --> 00:30:29,480 Speaker 1: solidify first. So some years ago some colleagues of mine 418 00:30:30,000 --> 00:30:32,440 Speaker 1: did some research, so they looked a little bit of 419 00:30:32,560 --> 00:30:35,040 Speaker 1: damage to the retina at the back of the eye 420 00:30:35,600 --> 00:30:38,680 Speaker 1: in an adult and looked at how that cause changes 421 00:30:39,000 --> 00:30:41,280 Speaker 1: in the back of the brain and the visual cortex. 422 00:30:41,960 --> 00:30:45,640 Speaker 1: And they assumed that because the visual cortex was not 423 00:30:45,680 --> 00:30:48,720 Speaker 1: getting any information from that little patch of eye, that 424 00:30:48,880 --> 00:30:52,560 Speaker 1: it would readjust you'd see plasticity. And to their surprise, 425 00:30:53,400 --> 00:30:58,240 Speaker 1: they found no measurable changes in the visual cortex. The 426 00:30:58,360 --> 00:31:01,440 Speaker 1: part of the cortex that was inactive because it wasn't 427 00:31:01,440 --> 00:31:05,240 Speaker 1: getting any data stayed inactive. It didn't get taken over 428 00:31:05,320 --> 00:31:09,920 Speaker 1: by the surrounding areas. Now, given the history of brain 429 00:31:10,000 --> 00:31:15,200 Speaker 1: plasticity studies even in adults, that was a little bit unexpected. 430 00:31:15,240 --> 00:31:18,720 Speaker 1: After all, you still have a lot of flexibility in 431 00:31:18,760 --> 00:31:22,040 Speaker 1: the parts of your brain that drive the body or 432 00:31:22,120 --> 00:31:24,600 Speaker 1: feel from the body, and this is what allows you 433 00:31:24,640 --> 00:31:28,120 Speaker 1: to learn how to hang gliders, snowboard even in your 434 00:31:28,200 --> 00:31:32,480 Speaker 1: later years. So what was the difference between the studies 435 00:31:32,520 --> 00:31:38,920 Speaker 1: involving your visual system versus the systems that drive your 436 00:31:38,960 --> 00:31:42,080 Speaker 1: body or feel from your body. Why are the patterns 437 00:31:42,080 --> 00:31:45,920 Speaker 1: in the primary visual cortex locked into place after a 438 00:31:46,040 --> 00:31:48,960 Speaker 1: short window of a few years, while the parts of 439 00:31:49,000 --> 00:31:53,160 Speaker 1: your body involved in moving your sensing continue to learn 440 00:31:54,240 --> 00:31:58,000 Speaker 1: The answer is that different areas of the brain operate 441 00:31:58,160 --> 00:32:04,240 Speaker 1: on different schedules of plasticity. Some neural networks are unyielding 442 00:32:04,320 --> 00:32:09,160 Speaker 1: and others are highly pliable. Some sensitive periods are really 443 00:32:09,240 --> 00:32:11,800 Speaker 1: brief and others are long. Okay, So is there a 444 00:32:12,080 --> 00:32:19,080 Speaker 1: general principle at work behind this diversity. One possibility is 445 00:32:19,080 --> 00:32:23,120 Speaker 1: that the different sensitive periods are caused by different underlying 446 00:32:23,800 --> 00:32:27,640 Speaker 1: learning strategies in different parts of the brain. So, in 447 00:32:27,680 --> 00:32:32,520 Speaker 1: this view, some regions are geared to learn throughout life 448 00:32:32,560 --> 00:32:36,840 Speaker 1: because they're meant to encode changeable details of the world. 449 00:32:37,360 --> 00:32:41,240 Speaker 1: So think of vocabulary words, or the ability to learn 450 00:32:41,720 --> 00:32:46,240 Speaker 1: new map directions, or the visual recognition of people's faces. 451 00:32:46,280 --> 00:32:50,120 Speaker 1: These are tasks for which you want to retain flexibility. 452 00:32:50,600 --> 00:32:55,080 Speaker 1: But in contrast, other brain areas are involved in really 453 00:32:55,160 --> 00:32:59,320 Speaker 1: stable relationships, like the building blocks of vision, or how 454 00:32:59,320 --> 00:33:02,960 Speaker 1: to chew food food or the general rules of grammar, 455 00:33:03,360 --> 00:33:08,920 Speaker 1: and these areas require a faster lockdown. But how could 456 00:33:08,920 --> 00:33:12,480 Speaker 1: the brain know and advance the order in which to 457 00:33:12,520 --> 00:33:18,160 Speaker 1: solidify things? Is that genetically encoded? Possibly some aspects are, 458 00:33:18,400 --> 00:33:22,280 Speaker 1: but I've previously published a new hypothesis about this, which 459 00:33:22,320 --> 00:33:25,760 Speaker 1: is that the degree of plasticity in a brain region 460 00:33:26,400 --> 00:33:30,880 Speaker 1: reflects how much the data change or are likely to 461 00:33:31,000 --> 00:33:34,080 Speaker 1: change in the outside world. So let me explain this. 462 00:33:34,560 --> 00:33:39,960 Speaker 1: If the incoming data aren't changing, the system hardens around that. 463 00:33:40,560 --> 00:33:43,400 Speaker 1: But if the data are constantly changing, then the system 464 00:33:43,720 --> 00:33:49,200 Speaker 1: remains flexible for that area. So as a result, stable 465 00:33:49,320 --> 00:33:54,480 Speaker 1: data solidify. First, let me give an example. Take information 466 00:33:54,640 --> 00:33:59,040 Speaker 1: from the ears versus information from the body. So areas 467 00:33:59,160 --> 00:34:02,360 Speaker 1: encoding the base six sounds of the world. Like the 468 00:34:02,400 --> 00:34:08,640 Speaker 1: primary auditory cortex, these become resistant to change. They stiffen rapidly. 469 00:34:08,960 --> 00:34:11,680 Speaker 1: And that's why, as I spoke about in a previous 470 00:34:11,719 --> 00:34:15,200 Speaker 1: episode thirty five, a baby born in America and a 471 00:34:15,239 --> 00:34:19,120 Speaker 1: baby born in Japan will learn how to hear different 472 00:34:19,280 --> 00:34:23,000 Speaker 1: possible sounds, and by nine months of age, their brain 473 00:34:23,080 --> 00:34:26,840 Speaker 1: is locking down on those sounds in their language. But 474 00:34:27,360 --> 00:34:31,799 Speaker 1: in contrast, the parts of your brain involved in navigating 475 00:34:31,840 --> 00:34:35,479 Speaker 1: your body and feeling from your body, these remain more 476 00:34:35,640 --> 00:34:40,840 Speaker 1: plastics throughout your life. Why because body plans change throughout 477 00:34:40,880 --> 00:34:44,520 Speaker 1: your life. You get heavier or skinnier, you put on 478 00:34:44,719 --> 00:34:48,439 Speaker 1: boots or slippers, or you're on crutches, or you jump 479 00:34:48,440 --> 00:34:52,880 Speaker 1: on a bicycle or a scooter or a trampoline, and 480 00:34:52,920 --> 00:34:55,520 Speaker 1: that's why you can pick up something new as an adult, 481 00:34:55,560 --> 00:34:59,400 Speaker 1: like windsurfing. The statistics of the language you're surrounding with 482 00:34:59,480 --> 00:35:03,759 Speaker 1: that doesn't change much, but your body's feedback from the 483 00:35:03,800 --> 00:35:08,840 Speaker 1: world does change, and as a result, the auditory cortex 484 00:35:09,040 --> 00:35:14,680 Speaker 1: tightens down, but less so for your body plan. So 485 00:35:14,719 --> 00:35:18,200 Speaker 1: now let's zoom into a single sense like vision. This 486 00:35:18,320 --> 00:35:21,480 Speaker 1: is really cool because in low level visual areas, what's 487 00:35:21,520 --> 00:35:25,840 Speaker 1: called the primary visual cortex, the neurons and code basic 488 00:35:25,960 --> 00:35:29,400 Speaker 1: properties of the world like edges and colors and angles. 489 00:35:29,920 --> 00:35:33,360 Speaker 1: But you have these higher areas of visual cortex that 490 00:35:33,400 --> 00:35:37,239 Speaker 1: are involved in more particular items like the layout of 491 00:35:37,320 --> 00:35:42,000 Speaker 1: your street, or the sleek look of this year's sports car, 492 00:35:42,440 --> 00:35:46,640 Speaker 1: or the arrangement of apps on your cell phone. Now, 493 00:35:46,719 --> 00:35:51,160 Speaker 1: the information in the low level areas that becomes established first, 494 00:35:51,520 --> 00:35:55,520 Speaker 1: and the successive layers wire up on top of those foundations, 495 00:35:56,520 --> 00:35:59,840 Speaker 1: so the possible angles of a line, these are fixed 496 00:35:59,840 --> 00:36:03,239 Speaker 1: in place. But you can still learn the face of 497 00:36:03,280 --> 00:36:07,600 Speaker 1: the latest movie star. So there's a hierarchy of flexibility 498 00:36:07,640 --> 00:36:11,799 Speaker 1: where the representations at the bottom are learned first. These 499 00:36:11,840 --> 00:36:15,439 Speaker 1: reflect the basic statistics of the visual world, and those 500 00:36:15,480 --> 00:36:20,120 Speaker 1: are unlikely to change, these remain stable so that the 501 00:36:20,440 --> 00:36:25,319 Speaker 1: higher order patterns, which can change more rapidly, they can 502 00:36:25,360 --> 00:36:28,480 Speaker 1: be learned. Okay, so let's do an analogy. If you 503 00:36:28,600 --> 00:36:32,520 Speaker 1: are building a library, you want to nail down the 504 00:36:32,560 --> 00:36:36,640 Speaker 1: basics first. You establish the positions of the shelves, and 505 00:36:36,680 --> 00:36:40,000 Speaker 1: you set up the Dewey decimal system for organization and 506 00:36:40,120 --> 00:36:43,400 Speaker 1: maybe the workflow for checking out the books. Once that's 507 00:36:43,440 --> 00:36:48,320 Speaker 1: all nailed down, then it's straightforward to maintain a flexible 508 00:36:48,440 --> 00:36:52,839 Speaker 1: inventory of books. You expand the offerings and exciting categories, 509 00:36:52,920 --> 00:36:58,000 Speaker 1: you reduce outdated volumes, and you constantly test out new titles. 510 00:36:58,360 --> 00:37:00,760 Speaker 1: This is the same thing in the brain. The primary 511 00:37:00,840 --> 00:37:04,120 Speaker 1: visual cortex gets all nailed down and set up first, 512 00:37:04,520 --> 00:37:07,560 Speaker 1: and higher order areas of the brain can try out 513 00:37:07,640 --> 00:37:12,400 Speaker 1: new things and remain flexible. So there's no single answer 514 00:37:12,440 --> 00:37:15,439 Speaker 1: to whether the brain is plastic as we get older. 515 00:37:15,480 --> 00:37:19,960 Speaker 1: It depends on what brain area we're talking about. Plasticity 516 00:37:20,400 --> 00:37:24,880 Speaker 1: declines with age, but across the brain it declines differently, 517 00:37:25,360 --> 00:37:30,400 Speaker 1: steeply or shallowly, depending on its function. Now, interestingly, this 518 00:37:30,520 --> 00:37:36,080 Speaker 1: hypothesis that the amount of plasticity reflects the variance in 519 00:37:36,120 --> 00:37:39,319 Speaker 1: the outside world. This has an analogy I think in 520 00:37:39,440 --> 00:37:43,759 Speaker 1: genetics in ways that science is still working to understand, 521 00:37:44,200 --> 00:37:49,120 Speaker 1: genomes seem to lock in some parts of their nucleotide 522 00:37:49,200 --> 00:37:54,200 Speaker 1: sequences the actgs. They lock in some parts more than others, 523 00:37:54,360 --> 00:37:59,440 Speaker 1: and they protect them against mutation, and conversely, other regions 524 00:37:59,480 --> 00:38:03,120 Speaker 1: of the chromes are much more variable. So, roughly speaking, 525 00:38:03,680 --> 00:38:09,319 Speaker 1: the variability of a genetic sequence mirrors the variability of 526 00:38:09,440 --> 00:38:14,280 Speaker 1: features in the outside world. For example, skin pigment genes 527 00:38:14,600 --> 00:38:19,000 Speaker 1: are highly variable because humans find themselves at different latitudes 528 00:38:19,239 --> 00:38:23,759 Speaker 1: and need to change the pigmentation to absorb enough vitamin D. 529 00:38:24,920 --> 00:38:29,279 Speaker 1: But in contrast, the genes that code for proteins that 530 00:38:29,320 --> 00:38:33,520 Speaker 1: break down sugar, these are really stable because that is 531 00:38:33,560 --> 00:38:38,600 Speaker 1: a critical and unchanging energy source. So by analogy in 532 00:38:38,640 --> 00:38:42,920 Speaker 1: the brain, I hypothesize that in the future we may 533 00:38:42,960 --> 00:38:48,680 Speaker 1: be able to quantify the variability of mental and social 534 00:38:48,760 --> 00:38:52,120 Speaker 1: and behavioral functions in human life, and we can put 535 00:38:52,160 --> 00:38:55,920 Speaker 1: to the test this hypothesis that the most flexible circuits 536 00:38:55,960 --> 00:39:18,680 Speaker 1: of the brain mirror the most variable parts of our environment. Okay, 537 00:39:18,920 --> 00:39:22,960 Speaker 1: so where does all this talk about brain plasticity put us. Well, 538 00:39:23,640 --> 00:39:28,080 Speaker 1: often what we find is that adults envy children. Why 539 00:39:28,200 --> 00:39:32,680 Speaker 1: because children have the ability to absorb languages at an 540 00:39:32,719 --> 00:39:37,319 Speaker 1: extraordinary rate, and they can think of magically bizarre approaches 541 00:39:37,360 --> 00:39:41,080 Speaker 1: to any problem, and they can celebrate the novelty of 542 00:39:41,120 --> 00:39:46,560 Speaker 1: every experience. But older brains have more closed doors, which 543 00:39:46,600 --> 00:39:50,279 Speaker 1: is why Toyber's World War Two veterans fared worse if 544 00:39:50,320 --> 00:39:54,800 Speaker 1: they were older, and why Arnold Schwarzenegger retains his accent. 545 00:39:55,840 --> 00:40:00,560 Speaker 1: And by analogy, the older a city is is the 546 00:40:00,560 --> 00:40:04,600 Speaker 1: more its infrastructure becomes resistant to shift. So look at 547 00:40:04,600 --> 00:40:09,200 Speaker 1: something like Rome. The city of Rome can't untangle its 548 00:40:09,280 --> 00:40:13,720 Speaker 1: windy roads to resemble the grid work of Manhattan because 549 00:40:13,840 --> 00:40:19,080 Speaker 1: too much history has glued its snaking roots into place. 550 00:40:20,320 --> 00:40:25,880 Speaker 1: Just like developing humans, cities deepen their tracks along early roads, 551 00:40:27,120 --> 00:40:30,560 Speaker 1: and so adults often wish they could have the plasticity 552 00:40:31,040 --> 00:40:34,680 Speaker 1: that they used to. In nineteen eighty four, at the 553 00:40:34,719 --> 00:40:38,840 Speaker 1: age of thirty five, the physicist my friend Alan Lightman 554 00:40:38,960 --> 00:40:42,040 Speaker 1: wrote a short essay in The New York Times titled 555 00:40:42,200 --> 00:40:48,400 Speaker 1: Elapsed Expectations, in which he lamented the perceived stiffening of 556 00:40:48,480 --> 00:40:52,480 Speaker 1: his mind. Here's what he said. Quote. The limber years 557 00:40:52,520 --> 00:40:57,920 Speaker 1: for scientists, as for athletes, generally come at a young age. 558 00:40:58,000 --> 00:41:01,280 Speaker 1: Isaac Newton was in his early twenties when he discovered 559 00:41:01,320 --> 00:41:05,399 Speaker 1: the law of gravity, Albert Einstein was twenty six when 560 00:41:05,400 --> 00:41:10,480 Speaker 1: he formulated special relativity, and James Clerk Maxwell had polished 561 00:41:10,480 --> 00:41:14,800 Speaker 1: off electromagnetic theory and retired to the country. By thirty five. 562 00:41:16,000 --> 00:41:19,000 Speaker 1: Lightman goes on to say, quote, when I hit thirty 563 00:41:19,040 --> 00:41:23,080 Speaker 1: five myself some months ago, I went through the unpleasant 564 00:41:23,120 --> 00:41:27,320 Speaker 1: but irresistible exercise of summing up my career in physics. 565 00:41:27,800 --> 00:41:31,200 Speaker 1: By this age or another few years, the most creative 566 00:41:31,200 --> 00:41:35,040 Speaker 1: achievements are finished and visible. You've either got the stuff 567 00:41:35,080 --> 00:41:39,040 Speaker 1: and used it, or you haven't. End quote. So Lightman 568 00:41:39,480 --> 00:41:44,680 Speaker 1: was concerned that his brain plasticity was stiffening into place, 569 00:41:45,000 --> 00:41:49,240 Speaker 1: and these same sentiments were echoed by the physicist James 570 00:41:49,280 --> 00:41:52,880 Speaker 1: Gates in a television interview I saw. He said, quote, 571 00:41:53,600 --> 00:41:57,799 Speaker 1: there's a saying that old physicists accept new ideas when 572 00:41:57,840 --> 00:42:02,600 Speaker 1: they die. It's the next general that brings new ideas 573 00:42:02,880 --> 00:42:05,239 Speaker 1: to their full fruition. When you get to be an 574 00:42:05,239 --> 00:42:08,520 Speaker 1: old physicist like me, you know a lot of stuff, 575 00:42:09,080 --> 00:42:11,600 Speaker 1: and it acts like a ballast on a ship. It 576 00:42:11,719 --> 00:42:15,000 Speaker 1: pulls you down. You have all the weight of these 577 00:42:15,040 --> 00:42:18,920 Speaker 1: other things that you know, and sometimes an idea like 578 00:42:18,960 --> 00:42:23,560 Speaker 1: a small ferry or a sprite passes by and you say, ah, 579 00:42:23,600 --> 00:42:25,640 Speaker 1: I don't know what that is, but it can't be 580 00:42:25,800 --> 00:42:31,120 Speaker 1: very important. Well, sometimes it is end quote. So this 581 00:42:31,360 --> 00:42:36,959 Speaker 1: kind of lamentation is typical of people as they age. 582 00:42:37,200 --> 00:42:42,960 Speaker 1: But happily, although brain plasticity diminishes over the years, it 583 00:42:43,000 --> 00:42:48,600 Speaker 1: is still present. Live wiring is not solely the privilege 584 00:42:48,640 --> 00:42:53,920 Speaker 1: of the young. Neural reconfiguration is an ongoing process that 585 00:42:54,040 --> 00:42:59,560 Speaker 1: lasts throughout our lives. We form new ideas, we accumulate 586 00:42:59,640 --> 00:43:05,040 Speaker 1: fresh information, we remember people and events that we're seeing now. 587 00:43:05,360 --> 00:43:10,320 Speaker 1: So going back to this analogy, despite having decreased flexibility, 588 00:43:10,680 --> 00:43:15,359 Speaker 1: the city of Rome still evolves. Rome now isn't what 589 00:43:15,400 --> 00:43:19,400 Speaker 1: it was twenty years ago. Today its statues are ringed 590 00:43:19,400 --> 00:43:24,600 Speaker 1: with cell phone towers and internet cafes. Although the rudiments 591 00:43:24,640 --> 00:43:28,680 Speaker 1: of the city are difficult to change, Rome nonetheless advances 592 00:43:28,719 --> 00:43:32,480 Speaker 1: all its finer points according to new circumstances, just like 593 00:43:32,840 --> 00:43:37,000 Speaker 1: the library changes its stock of books while its architecture 594 00:43:37,040 --> 00:43:40,920 Speaker 1: remains largely set. And you see this in so many 595 00:43:41,280 --> 00:43:45,200 Speaker 1: neuroscience studies. For example, when adults learn a new task 596 00:43:45,400 --> 00:43:49,000 Speaker 1: like juggling, you can see major changes in their brains. 597 00:43:49,520 --> 00:43:52,440 Speaker 1: If they take up a new musical instrument, you see 598 00:43:52,480 --> 00:43:56,960 Speaker 1: these major changes. If they become a London taxi driver 599 00:43:57,400 --> 00:44:02,120 Speaker 1: and memorize enormous maps of London, you can see these changes. 600 00:44:02,200 --> 00:44:08,320 Speaker 1: And all of these involve adult plasticity. One really stunning 601 00:44:08,400 --> 00:44:13,080 Speaker 1: example emerged recently from this nun study called the Religious 602 00:44:13,160 --> 00:44:17,640 Speaker 1: Order Study, which is a multi decade investigation of hundreds 603 00:44:17,680 --> 00:44:22,440 Speaker 1: of Catholic nuns living in convents. So all these sisters 604 00:44:22,480 --> 00:44:26,319 Speaker 1: agreed to regularly test their cognitive function and share their 605 00:44:26,360 --> 00:44:30,640 Speaker 1: medical records, and when they die, they donate their brains. 606 00:44:31,400 --> 00:44:36,520 Speaker 1: So amazingly, many of these nuns never displayed any cognitive decline. 607 00:44:36,560 --> 00:44:39,760 Speaker 1: They were sharp as a whip, but yet their brains 608 00:44:39,800 --> 00:44:45,800 Speaker 1: at autopsy were riddled with Alzheimer's disease. In other words, 609 00:44:45,840 --> 00:44:51,759 Speaker 1: their neural networks were physically degenerating, but their performance was not. 610 00:44:52,760 --> 00:44:55,879 Speaker 1: Now what could explain that, well, the key is that 611 00:44:56,520 --> 00:45:00,239 Speaker 1: the nuns and their convents had to consistently use their 612 00:45:00,280 --> 00:45:04,719 Speaker 1: wits until their final days. They had responsibilities and chores 613 00:45:05,080 --> 00:45:09,160 Speaker 1: and social lives and arguments and game nights and group 614 00:45:09,239 --> 00:45:15,080 Speaker 1: discussions and so on. So unlike typical retirees, they didn't 615 00:45:15,400 --> 00:45:18,120 Speaker 1: PLoP onto a couch in front of a television set. 616 00:45:18,480 --> 00:45:23,560 Speaker 1: Because they had active mental lives, their brains were forced 617 00:45:23,680 --> 00:45:27,719 Speaker 1: to constantly build new bridges, even as some of their 618 00:45:27,719 --> 00:45:31,960 Speaker 1: neural roadways were physically falling apart. What stunning is that 619 00:45:32,239 --> 00:45:36,000 Speaker 1: a third of the nuns seemed to have had the 620 00:45:36,080 --> 00:45:43,319 Speaker 1: molecular pathology of Alzheimer's without the expected cognitive symptoms. An 621 00:45:43,640 --> 00:45:48,120 Speaker 1: active mental life, even in the very elderly. This makes 622 00:45:48,280 --> 00:45:53,800 Speaker 1: new connections in the brain. So learning can happen in 623 00:45:54,040 --> 00:45:57,280 Speaker 1: any age, and the question is why is it slower 624 00:45:57,320 --> 00:46:01,880 Speaker 1: than as the brain matures. Well, one reason, as we've discussed, 625 00:46:01,960 --> 00:46:04,640 Speaker 1: is that many of the swinging doors have closed. But 626 00:46:04,680 --> 00:46:08,680 Speaker 1: there's another way to look at this. Remember that brain 627 00:46:08,920 --> 00:46:14,200 Speaker 1: changes are driven by the difference between your internal model 628 00:46:14,480 --> 00:46:18,160 Speaker 1: and what actually happens in the world, So brains make 629 00:46:18,320 --> 00:46:23,160 Speaker 1: change only when something is unexpected. As you learn all 630 00:46:23,200 --> 00:46:27,000 Speaker 1: this and figure this out, your brain becomes less challenged 631 00:46:27,080 --> 00:46:31,680 Speaker 1: through time, it becomes more settled into place. For example, 632 00:46:31,680 --> 00:46:35,480 Speaker 1: when you're a child, your internal model tells you that 633 00:46:35,880 --> 00:46:39,200 Speaker 1: all people believe everything that you believe, and as world 634 00:46:39,320 --> 00:46:44,000 Speaker 1: experience teaches you the difference between your predictions and your experience, 635 00:46:44,520 --> 00:46:48,279 Speaker 1: your networks are constantly having to adjust to address that 636 00:46:48,440 --> 00:46:52,200 Speaker 1: growing gap. Or consider what happens when you start a 637 00:46:52,239 --> 00:46:56,440 Speaker 1: new job. At first, everything is new, from your coworkers 638 00:46:56,480 --> 00:47:00,400 Speaker 1: to your responsibilities, to your approaches. You have all this 639 00:47:00,600 --> 00:47:03,840 Speaker 1: brain plasticity during the first days and weeks as you 640 00:47:03,920 --> 00:47:08,560 Speaker 1: incorporate your new gig into your internal model. But after 641 00:47:08,600 --> 00:47:13,120 Speaker 1: a while you become proficient at your job, so skill 642 00:47:13,719 --> 00:47:18,799 Speaker 1: replaces flexibility. And by the way, as an analogy, we 643 00:47:18,840 --> 00:47:22,680 Speaker 1: can see this pattern in the way that nations settle 644 00:47:22,800 --> 00:47:28,640 Speaker 1: into place. Consider the amendments to the constitution of any country. 645 00:47:28,880 --> 00:47:32,320 Speaker 1: Almost all the change happens near the beginning, while the 646 00:47:32,440 --> 00:47:36,320 Speaker 1: nation is learning the strategies of running itself, and later 647 00:47:36,880 --> 00:47:43,279 Speaker 1: constitutions congeal into place and amendments slow down. So take 648 00:47:43,320 --> 00:47:47,719 Speaker 1: the US Constitution. Twelve of the amendments took place in 649 00:47:47,760 --> 00:47:51,520 Speaker 1: the first thirteen years, and after that there were a 650 00:47:51,600 --> 00:47:54,600 Speaker 1: maximum of four changes in any twenty year period, and 651 00:47:54,600 --> 00:47:59,080 Speaker 1: most periods had no changes at all. And the latest change, 652 00:47:59,200 --> 00:48:01,960 Speaker 1: ratifying the t twenty seventh Amendment, that was in nineteen 653 00:48:02,040 --> 00:48:06,440 Speaker 1: ninety two, and the Constitution has been at a standstill 654 00:48:06,680 --> 00:48:13,200 Speaker 1: since then. In this way, nations steadily diminish their adaptation 655 00:48:13,320 --> 00:48:16,080 Speaker 1: to the world, because what they do is they profusely 656 00:48:16,160 --> 00:48:19,920 Speaker 1: modify at the beginning, and with time they settle on 657 00:48:20,040 --> 00:48:24,920 Speaker 1: a working model that offers what the country needs to 658 00:48:25,000 --> 00:48:31,120 Speaker 1: be operational. And in this same way, the brain's solidification 659 00:48:31,840 --> 00:48:38,000 Speaker 1: reflects its success in understanding the world. Neural networks lock 660 00:48:38,160 --> 00:48:42,240 Speaker 1: themselves more deeply into place, not because of fading function, 661 00:48:42,360 --> 00:48:47,319 Speaker 1: but because they've had success in figuring things out. So 662 00:48:48,400 --> 00:48:52,120 Speaker 1: would you really want the plasticity of a child again? 663 00:48:52,560 --> 00:48:56,000 Speaker 1: Although having a sponge like brain that absorbs everything that 664 00:48:56,200 --> 00:49:01,440 Speaker 1: sounds appealing, the game of life is largely about figuring 665 00:49:01,560 --> 00:49:07,080 Speaker 1: out the rules. What we lose in modifiability, we gain 666 00:49:07,360 --> 00:49:12,840 Speaker 1: in expertise our hard won neural networks. They might not 667 00:49:12,920 --> 00:49:16,439 Speaker 1: be correct about everything, or even internally consistent, but they 668 00:49:16,640 --> 00:49:22,399 Speaker 1: add up to life experience to know how to an 669 00:49:22,440 --> 00:49:26,200 Speaker 1: approach to the world. A child simply doesn't have the 670 00:49:26,239 --> 00:49:30,799 Speaker 1: capacity to run a company, or write about deep ideas 671 00:49:30,920 --> 00:49:36,080 Speaker 1: or lead a nation. If plasticity didn't decline, you couldn't 672 00:49:36,120 --> 00:49:39,279 Speaker 1: lock down the conventions of the world. You would never 673 00:49:39,800 --> 00:49:43,200 Speaker 1: learn the streets of your neighborhood or people's names, or 674 00:49:43,280 --> 00:49:45,600 Speaker 1: how to do a job, or how to navigate a 675 00:49:45,760 --> 00:49:50,279 Speaker 1: social life. You wouldn't be able to hold a meaningful conversation, 676 00:49:51,000 --> 00:49:54,560 Speaker 1: or ride a bike or obtain food for yourself. If 677 00:49:54,560 --> 00:49:59,520 Speaker 1: you had total flexibility, you would have the helplessness of 678 00:49:59,560 --> 00:50:04,520 Speaker 1: an in And don't forget that locking things down this 679 00:50:04,560 --> 00:50:08,239 Speaker 1: isn't just about skills that you learn. Locking things down 680 00:50:08,320 --> 00:50:12,520 Speaker 1: is what allows you to retain memories. Every single thing 681 00:50:12,560 --> 00:50:15,840 Speaker 1: you remember in your life, every bit of your story, 682 00:50:16,000 --> 00:50:21,000 Speaker 1: is stored in the exact patterns of your neural networks. 683 00:50:22,840 --> 00:50:27,760 Speaker 1: So just imagine that you had the opportunity to swallow 684 00:50:27,800 --> 00:50:32,280 Speaker 1: a capsule that would renew the brain plasticity even infant. 685 00:50:32,360 --> 00:50:36,840 Speaker 1: This would give you the capacity to reprogram your neural networks, 686 00:50:36,880 --> 00:50:41,080 Speaker 1: to learn new languages rapidly and adopt new accents and 687 00:50:41,360 --> 00:50:47,640 Speaker 1: new views of physics. But you'd forget everything that came before. 688 00:50:48,200 --> 00:50:52,279 Speaker 1: Your memories of your childhood would be erased and overwritten. 689 00:50:52,920 --> 00:50:56,040 Speaker 1: Memories of your first lover, your first trip to Disneyland, 690 00:50:56,400 --> 00:51:00,160 Speaker 1: your interaction with your parents all would fade like a 691 00:51:00,320 --> 00:51:04,960 Speaker 1: dream after waking. Would it be worth it to you? 692 00:51:04,960 --> 00:51:06,840 Speaker 1: You know? While I was working on my book LiveWire, 693 00:51:06,960 --> 00:51:10,960 Speaker 1: I was struck by thinking about a horror scenario in 694 00:51:11,000 --> 00:51:15,560 Speaker 1: the future of warfare, because in warfare, countries want to 695 00:51:15,680 --> 00:51:18,320 Speaker 1: injure their enemies, not kill them, because it requires a 696 00:51:18,360 --> 00:51:21,359 Speaker 1: lot more resource from the other side. They have to 697 00:51:21,400 --> 00:51:27,040 Speaker 1: attend to the wounded. So imagine a biological weapon that 698 00:51:27,239 --> 00:51:32,480 Speaker 1: implements broad brain plasticity. Again, no one is physically hurt, 699 00:51:32,960 --> 00:51:36,480 Speaker 1: but the troops are propelled back to the state of infants. 700 00:51:36,960 --> 00:51:40,239 Speaker 1: They forget their ability to walk into talk all if 701 00:51:40,280 --> 00:51:44,799 Speaker 1: their memories are wiped. When they're returned home by their commanders, 702 00:51:45,200 --> 00:51:49,000 Speaker 1: they have no remembrance of their families or friends, or 703 00:51:49,080 --> 00:51:53,800 Speaker 1: spouses or children. Technically, they're still fine, they can still learn. Again, 704 00:51:53,880 --> 00:51:57,840 Speaker 1: nothing is damaged, only their mental lives. The part we 705 00:51:57,920 --> 00:52:02,600 Speaker 1: can't see. These have been factory reset back to their 706 00:52:02,760 --> 00:52:07,560 Speaker 1: original state. Now, this scene is so horrific because fundamentally, 707 00:52:08,239 --> 00:52:14,000 Speaker 1: who you are is the sum total of your neural circuits. 708 00:52:14,320 --> 00:52:19,000 Speaker 1: Who you are is stored in the exact configuration of 709 00:52:19,040 --> 00:52:25,239 Speaker 1: the forest of eighty six billion neurons. So if you said, hey, 710 00:52:25,320 --> 00:52:29,320 Speaker 1: I want the plasticity of a child again, that comes 711 00:52:29,320 --> 00:52:33,200 Speaker 1: at the cost of who you are now and what 712 00:52:33,480 --> 00:52:37,200 Speaker 1: you know. So what we've seen today is that the 713 00:52:37,320 --> 00:52:40,759 Speaker 1: flexibility of a brain declines with age, and we saw 714 00:52:40,840 --> 00:52:44,640 Speaker 1: several examples where this can be sudden, like the closing 715 00:52:44,680 --> 00:52:47,200 Speaker 1: of a door, such that if you don't do something 716 00:52:47,239 --> 00:52:50,800 Speaker 1: before you're six or eight or thirteen, your brain simply 717 00:52:50,880 --> 00:52:53,640 Speaker 1: can't learn it later. And we also saw that there's 718 00:52:53,680 --> 00:52:55,880 Speaker 1: not just one door that closes in the brain, but 719 00:52:56,160 --> 00:52:59,840 Speaker 1: instead different doors close at different rates. So, for example, 720 00:52:59,840 --> 00:53:03,360 Speaker 1: you have to be exposed to language in your formative 721 00:53:03,520 --> 00:53:07,360 Speaker 1: early years to understand the concept of language. But the 722 00:53:07,440 --> 00:53:11,320 Speaker 1: question of whether you retain an accent after moving somewhere, 723 00:53:11,840 --> 00:53:15,000 Speaker 1: that's something that comes many years later. And of course, 724 00:53:15,320 --> 00:53:17,839 Speaker 1: you can learn a foreign language at any age, even 725 00:53:17,880 --> 00:53:20,719 Speaker 1: though it becomes more difficult. And I just want to 726 00:53:20,760 --> 00:53:25,719 Speaker 1: remind us about relevance here. In episode thirty five, I 727 00:53:25,800 --> 00:53:27,919 Speaker 1: talked about what sticks in your brain and what does 728 00:53:27,960 --> 00:53:30,120 Speaker 1: not stick in your brain, And the bottom line is 729 00:53:30,160 --> 00:53:34,080 Speaker 1: that your brain has to care about something in order 730 00:53:34,160 --> 00:53:36,800 Speaker 1: to learn it. You have to have the right cocktail 731 00:53:36,840 --> 00:53:42,400 Speaker 1: of neurotransmitters present, and that correlates with curiosity and relevance 732 00:53:42,440 --> 00:53:45,880 Speaker 1: to you. So you can definitely learn a language at 733 00:53:45,920 --> 00:53:50,400 Speaker 1: any age. The issue is simply do you have enough motivation. 734 00:53:51,080 --> 00:53:54,480 Speaker 1: If so, you can learn it. The problem is that 735 00:53:54,719 --> 00:53:58,480 Speaker 1: as people get older, there's typically less motivation to get 736 00:53:58,560 --> 00:54:01,480 Speaker 1: really good at something like a foreign language, because you 737 00:54:01,480 --> 00:54:03,840 Speaker 1: can get by with the language that you have, or 738 00:54:03,880 --> 00:54:06,719 Speaker 1: you figure out the minimum of that language that you 739 00:54:06,760 --> 00:54:08,480 Speaker 1: need to learn, so you can get a few things 740 00:54:08,680 --> 00:54:11,760 Speaker 1: and you don't really care as much about impressing people 741 00:54:11,800 --> 00:54:15,920 Speaker 1: with your fluency. But the mechanisms are still available and 742 00:54:15,960 --> 00:54:19,040 Speaker 1: you can learn it if it's important to you. And 743 00:54:19,080 --> 00:54:20,960 Speaker 1: I think one of the tricks in life is figuring 744 00:54:21,000 --> 00:54:26,440 Speaker 1: out how to fool yourself using your psychology to influence 745 00:54:26,520 --> 00:54:31,640 Speaker 1: your biology by reminding yourself, hey, here's why this would 746 00:54:31,719 --> 00:54:34,680 Speaker 1: be important to me, and it can be anything. It 747 00:54:34,719 --> 00:54:37,279 Speaker 1: can be this is going to impress the person I 748 00:54:37,280 --> 00:54:39,160 Speaker 1: want to go on a date with, or this will 749 00:54:39,200 --> 00:54:41,440 Speaker 1: make me proud of myself, or this will get me 750 00:54:41,560 --> 00:54:44,600 Speaker 1: that promotion that I really want, or this will get 751 00:54:44,600 --> 00:54:47,280 Speaker 1: me into medical school, or this will make my parents prouder. 752 00:54:47,480 --> 00:54:51,279 Speaker 1: Whatever it is that drives you, it's really useful to 753 00:54:51,440 --> 00:54:56,480 Speaker 1: clarify that to yourself, to explicitly specify to yourself why 754 00:54:56,520 --> 00:55:00,520 Speaker 1: this task matters, and then you'll have that at write 755 00:55:00,520 --> 00:55:06,279 Speaker 1: cocktail of neurotransmitters to make that information stick because in 756 00:55:06,320 --> 00:55:09,920 Speaker 1: the end we get to be the sculptors of our 757 00:55:10,000 --> 00:55:16,480 Speaker 1: own brains. Go to eagleman dot com slash podcast for 758 00:55:16,520 --> 00:55:19,560 Speaker 1: more information and to find further reading. Send me an 759 00:55:19,560 --> 00:55:24,319 Speaker 1: email at podcasts at eagleman dot com with questions or discussions, 760 00:55:24,560 --> 00:55:27,439 Speaker 1: and I'm making sporadic episodes in which I address those 761 00:55:30,200 --> 00:55:34,680 Speaker 1: until next time. I'm David Eagleman, and this is Inner Cosmos.