WEBVTT - Ep38 "Why is it hard to teach an old brain new tricks?" 0:00:05.280 --> 0:00:09.960 Why does Arnold Schwarzenegger have an accent but Milakunis doesn't. 0:00:10.480 --> 0:00:13.920 And why is there a correlation between how tall a 0:00:14.000 --> 0:00:17.479 person is and how much his salary is likely to 0:00:17.520 --> 0:00:20.920 be Why does an elderly person have a hard time 0:00:21.120 --> 0:00:24.439 learning a new language but no trouble learning the name 0:00:24.520 --> 0:00:27.400 and face of a new movie star. What would we 0:00:27.600 --> 0:00:30.960 mean by saying that you are born as many people 0:00:31.600 --> 0:00:38.839 but die as a single one. Welcome to the inner 0:00:39.000 --> 0:00:42.320 cosmos with me, David Eagleman. I'm a neuroscientist and author 0:00:42.360 --> 0:00:46.920 at Stanford, and in these episodes we sail deeply into 0:00:46.960 --> 0:00:51.319 our three pound universe to understand why and how our 0:00:51.440 --> 0:01:02.440 lives look the way they do. Today's episode is about 0:01:02.920 --> 0:01:06.480 brain plasticity, which is the ability of the brain to 0:01:06.520 --> 0:01:12.480 modify itself and how this changes throughout your lifetime. So 0:01:12.520 --> 0:01:16.000 we're going to address why it is harder to teach 0:01:16.080 --> 0:01:19.880 an old dog new tricks and ask whether that is 0:01:19.920 --> 0:01:26.480 always true. So let's start fifty years ago. There was 0:01:26.560 --> 0:01:31.280 a psychologist named Hans Lucas Touber at Mit and he 0:01:31.360 --> 0:01:36.160 got curious about what had happened to soldiers who had 0:01:36.200 --> 0:01:40.320 sustained head injuries in World War two. Now, this was 0:01:40.360 --> 0:01:43.319 in the nineteen seventies, so the war had been almost 0:01:43.400 --> 0:01:47.560 thirty years earlier. So he tracked down five hundred and 0:01:47.640 --> 0:01:51.640 twenty men who had sustained brain damage during the battles, 0:01:52.200 --> 0:01:56.080 and some had fared well in their recovery, but others 0:01:56.560 --> 0:01:59.720 didn't have such good outcomes, and Toyber wanted to understand 0:01:59.760 --> 0:02:03.600 what the difference was. So he scoured all the records 0:02:03.960 --> 0:02:06.840 and he looked for the things that correlated with good 0:02:06.880 --> 0:02:09.760 outcomes and bad outcomes. And you know what he found. 0:02:10.400 --> 0:02:14.760 The younger the soldier was when he got the head injury, 0:02:14.919 --> 0:02:17.799 the better he was now. And the older the soldier, 0:02:18.320 --> 0:02:23.840 the more permanent the damage. Why it's because younger brains 0:02:23.960 --> 0:02:28.920 are more flexible. There's more brain plasticity, which means the 0:02:28.960 --> 0:02:33.760 ability of the circuitry to reconfigure itself, and so if 0:02:33.760 --> 0:02:37.480 there's damage, a young brain can do what it needs 0:02:37.520 --> 0:02:41.760 to to rewrite its circuitry and get itself back on track. 0:02:42.400 --> 0:02:45.920 Now you know that I love analogies, So here's Today's 0:02:46.880 --> 0:02:50.560 brains are like a map of Europe where you look 0:02:50.680 --> 0:02:55.400 at the borders between the countries. So think of a 0:02:55.440 --> 0:02:59.240 young brain like Europe five thousand years ago, and if 0:02:59.280 --> 0:03:03.560 you can imagine different historical trajectories that could have happened, 0:03:04.080 --> 0:03:07.960 the borders could have evolved in many ways. There's nothing 0:03:08.320 --> 0:03:12.520 fundamental about where the borders between the countries sit today, 0:03:13.639 --> 0:03:19.200 But today, after millennia of human history, the maps are 0:03:19.240 --> 0:03:23.240 more settled into place. Now that humans have had centuries 0:03:23.320 --> 0:03:28.720 to clang swords and discharge rifles, you get these territory 0:03:28.840 --> 0:03:32.400 borders that are kind of stubborn to change. So think 0:03:32.440 --> 0:03:37.440 of the borders between France and Italy and Switzerland. These 0:03:37.440 --> 0:03:41.360 are totally arbitrary lines, but they're not likely to change 0:03:41.400 --> 0:03:47.200 now because you don't have roving bands of marauders anymore 0:03:47.400 --> 0:03:51.920 or bearded conquerors leading big horse armies. These things have 0:03:51.960 --> 0:03:57.160 been replaced with the United Nations and international rules of engagement, 0:03:57.840 --> 0:04:02.520 and economies have gotten increased seemly dependent on information and 0:04:02.600 --> 0:04:07.440 expertise rather than on treasures that you can go pillage. 0:04:08.200 --> 0:04:13.760 So even in the face of trade arguments and immigration debates, 0:04:14.080 --> 0:04:18.320 the boundaries between European countries are really hard to move. 0:04:19.040 --> 0:04:22.920 For the most part, the nations have settled into place, 0:04:23.640 --> 0:04:27.960 so the land mass began with lots of possibilities for 0:04:28.080 --> 0:04:32.919 where the borders sat essentially infinite possibility, but with time 0:04:33.560 --> 0:04:39.640 the potential has narrowed, the map solidified into place, and 0:04:39.720 --> 0:04:43.400 now it's not so easy to make big changes. The 0:04:43.520 --> 0:04:50.520 brain matures like Europe through years of border disputes within 0:04:50.600 --> 0:04:57.680 neural networks, the maps become increasingly solidified. So as a result, 0:04:58.279 --> 0:05:02.240 brain injury is really dangerous for the elderly, but it's 0:05:02.360 --> 0:05:06.760 less dangerous for the young because an older brain can't 0:05:06.800 --> 0:05:12.880 easily reassign settled territories for new tasks. But a brain 0:05:12.960 --> 0:05:17.000 that's at the dawn of its wars can still reimagine 0:05:17.040 --> 0:05:23.000 its maps. Okay, so think about the trajectory of a 0:05:23.120 --> 0:05:28.320 human life. So imagine a young baby born somewhere sometime. 0:05:28.800 --> 0:05:34.760 When she's first born. Her brain has unbelievable flexibility wherever 0:05:35.000 --> 0:05:39.080 and whenever she drops out of the womb. She will 0:05:39.200 --> 0:05:42.440 soak up the local language. She'll pick up on the 0:05:42.480 --> 0:05:45.240 subtle details of her culture and what to wear and 0:05:45.279 --> 0:05:49.919 how to act. She will absorb the local religious beliefs. 0:05:50.000 --> 0:05:53.279 She'll learn all of the rules around her. She'll learn 0:05:53.600 --> 0:05:58.200 how to gather massive amounts of information, and depending on 0:05:58.640 --> 0:06:03.919 her generation, that might be by unrolling a scroll or 0:06:03.920 --> 0:06:06.880 flipping through the pages of a book or swiping the 0:06:07.000 --> 0:06:12.680 screen of a small rectangle. But by the time she's grown, 0:06:13.680 --> 0:06:18.760 that story of flexibility has changed somewhat. Her brain isn't 0:06:18.800 --> 0:06:23.480 so flexible now. She belongs to a particular political party, 0:06:24.080 --> 0:06:28.640 and she's unlikely to change. She plays the piano reasonably well, 0:06:28.960 --> 0:06:32.400 but she doesn't have any particular interest in studying violin 0:06:32.560 --> 0:06:35.640 or other instruments. She likes to cook, and all of 0:06:35.680 --> 0:06:40.200 her dishes exploit combinations of the fourteen ingredients that she 0:06:40.320 --> 0:06:44.280 is used to. She spends her online time with a 0:06:44.440 --> 0:06:48.719 vanishingly small fraction of the billions of available web pages. 0:06:49.680 --> 0:06:53.039 She has a respectable golf game, but she doesn't have 0:06:53.080 --> 0:06:57.040 any curiosity about other sports. She lives in a city 0:06:57.040 --> 0:07:00.479 of eight million people, but she only has three close friends. 0:07:01.120 --> 0:07:03.880 She isn't particularly interested in the science that she didn't 0:07:03.920 --> 0:07:07.400 already learn in school. When she goes to the store, 0:07:07.680 --> 0:07:11.480 she passes racks of shirts until she finds the kind 0:07:11.600 --> 0:07:14.440 that she always wears, and she selects two of them 0:07:14.480 --> 0:07:18.960 in her standard colors. Her haircut is the same as 0:07:18.960 --> 0:07:22.360 it was since she was a teenager. Okay, so this 0:07:22.400 --> 0:07:26.920 sort of life trajectory underscores a general point, and we've 0:07:26.920 --> 0:07:30.440 all seen this before, which is that babies are born 0:07:30.800 --> 0:07:33.120 with not many built in skills, and they have a 0:07:33.240 --> 0:07:38.120 ton of plasticity. They can learn anything, while adults have 0:07:38.400 --> 0:07:43.560 mastered specific tasks, but at the expense of flexibility. So 0:07:43.640 --> 0:07:50.120 there's a trade off between adaptability and efficiency. So as 0:07:50.160 --> 0:07:54.280 your brain gets good at certain jobs, it becomes less 0:07:54.400 --> 0:07:58.800 able to tackle others. Now, just to be clear, this 0:07:58.880 --> 0:08:02.320 is not to say that adam dults aren't intelligent. In fact, 0:08:02.400 --> 0:08:05.360 it's just the opposite. An adult can do all kinds 0:08:05.400 --> 0:08:07.840 of things that a baby can't. An adult can run 0:08:07.880 --> 0:08:11.320 a company, or fix an air conditioner, or plan a 0:08:11.360 --> 0:08:17.720 business takeover precisely because the adult's brain understands things about 0:08:17.720 --> 0:08:21.320 the functioning of the world that a child's brain just 0:08:21.600 --> 0:08:25.480 can't understand. So the way we capture this concept is 0:08:25.520 --> 0:08:30.560 to say that the baby's brain has fluid intelligence, meaning 0:08:30.560 --> 0:08:36.880 they can learn anything, while adult brains have crystallized intelligence. So, 0:08:37.040 --> 0:08:40.920 for example, a few episodes ago, I mentioned a story 0:08:41.000 --> 0:08:45.560 about the violinist Yittsawk Pearlman, in which a fan told 0:08:45.679 --> 0:08:48.360 him that he would give his life to play like that, 0:08:48.559 --> 0:08:53.400 and Pearlman said, I did what Pearlman was pointing to 0:08:53.559 --> 0:08:56.360 is a fact of life. To get good at one 0:08:56.400 --> 0:09:00.200 thing is to close the door on other things. So 0:09:00.640 --> 0:09:04.400 Pearlman went from presumably being able to tackle any instrument 0:09:04.760 --> 0:09:09.439 to being superlative at one at the expense of everything else. 0:09:09.520 --> 0:09:14.479 It's unlikely that Pearlman could also be a professional baseball 0:09:14.520 --> 0:09:18.280 player in the same lifetime. Why because you have only 0:09:18.320 --> 0:09:22.680 one single life, and what you devote yourself to sends 0:09:22.720 --> 0:09:26.760 you down particular roads. But that means that all the 0:09:26.960 --> 0:09:33.040 other roads will forever remain untrodden by you. And this 0:09:33.160 --> 0:09:37.360 is what the philosopher Martin Heidegger was pointing to when 0:09:37.440 --> 0:09:42.080 he said, quote every man is born as many men 0:09:42.679 --> 0:09:47.280 and dies as a single one end quote. You're born 0:09:47.600 --> 0:09:50.800 with lots of possibility, but when you die, you are 0:09:51.080 --> 0:09:55.959 just the limited you. Now, from the point of view 0:09:56.040 --> 0:09:59.680 of your neural networks, what does it mean to descend 0:09:59.720 --> 0:10:04.040 into pattern and habit? So here's another analogy to help 0:10:04.120 --> 0:10:08.800 us picture this. Imagine two villages a few miles apart. 0:10:09.320 --> 0:10:13.080 So people interested in going from one settlement over to 0:10:13.080 --> 0:10:17.640 the other one, they take all possible paths. Some travelers 0:10:18.160 --> 0:10:22.600 walk the scenic route along the ridgetops, but others prefer 0:10:22.679 --> 0:10:26.600 the shade of the cliff side, and some people move 0:10:26.640 --> 0:10:30.360 among the slippery rocks by the river, and others take 0:10:30.400 --> 0:10:35.200 the riskier but faster route through the woods. Okay, with 0:10:35.400 --> 0:10:41.520 time and experience, one route ends up proving more popular. 0:10:41.559 --> 0:10:45.280 Maybe it makes better sense or it's faster. But eventually 0:10:45.440 --> 0:10:50.120 that path becomes grooved where the most people have walked, 0:10:50.440 --> 0:10:55.959 and it starts to become the standard. After some years 0:10:55.960 --> 0:11:00.280 go by, the local government lays down roadways, and after 0:11:00.280 --> 0:11:04.320 a few decades that expands into highways, and now the 0:11:04.360 --> 0:11:08.400 way to get from here to there is really nailed down. 0:11:09.400 --> 0:11:14.679 So you started with broad optionality, but eventually that gets 0:11:14.720 --> 0:11:19.320 reduced to the standard path. And this is what happens 0:11:19.760 --> 0:11:25.520 inside brains. They begin with almost infinite possible routes through 0:11:25.640 --> 0:11:32.199 the neural networks, but with time the practiced pathways become 0:11:32.280 --> 0:11:39.000 difficult to exit, the unused paths become thinned away. So 0:11:39.160 --> 0:11:43.600 through decades of experience, the brain comes to physically represent 0:11:44.320 --> 0:11:50.960 your world, and your decisions follow the remaining hard paved paths. 0:11:51.920 --> 0:11:53.480 I mean, just think about what it would be like 0:11:53.600 --> 0:11:56.360 if you were born with your genes and your brain 0:11:56.920 --> 0:12:00.640 in a different part of the world. Maybe a different 0:12:00.679 --> 0:12:03.840 generation a thousand years ago or maybe a thousand years 0:12:03.880 --> 0:12:08.360 from now. You would function and thrive in whatever environment 0:12:08.400 --> 0:12:12.119 you drop into, but you'd speak a totally different language, 0:12:12.559 --> 0:12:16.360 you'd have a different religion, you would believe different things 0:12:16.440 --> 0:12:20.520 about the world. But as it happens to have turned out, 0:12:20.559 --> 0:12:22.880 you were born in your hometown, and you grew up 0:12:22.960 --> 0:12:26.920 with your language and your parents, and so all of 0:12:26.960 --> 0:12:32.680 the us that could have been ended up getting thinned away. 0:12:34.040 --> 0:12:38.720 Now that might sound sad to lose the optionality, but 0:12:38.840 --> 0:12:43.959 the upside of a solidifying brain is that you end 0:12:44.080 --> 0:12:49.440 up with lightning fast ways of solving problems. Now, the 0:12:49.480 --> 0:12:54.040 downside is that it's harder to attack new problems with wild, 0:12:54.280 --> 0:12:59.560 unstructured inventiveness. Now, from the neuroscience point of view, there's 0:12:59.600 --> 0:13:04.000 also a second reason why older brains are less flexible, 0:13:04.040 --> 0:13:08.240 and this is beyond the diminishing optionality in the pathways issue. 0:13:08.640 --> 0:13:12.800 When older brains make changes, they do so only in 0:13:12.920 --> 0:13:21.000 small spots. In contrast, baby's brains modify across vast territories, 0:13:21.559 --> 0:13:24.160 and this is because of chemicals in the brain called 0:13:24.160 --> 0:13:29.560 neurotransmitters that are broadcast broadly in a baby's brain, So 0:13:30.360 --> 0:13:35.520 in an infant brain, these chemicals like acetylcholine. They transmit 0:13:35.679 --> 0:13:39.480 announcements throughout the brain, saying, Hey, something important just happen, 0:13:40.000 --> 0:13:44.680 And this allows pathways and connections to change and modify. 0:13:45.160 --> 0:13:50.560 So a baby's brain is changeable throughout its territory, and 0:13:50.720 --> 0:13:55.040 over years its understanding of the world comes into focus 0:13:55.120 --> 0:14:00.520 like a polaroid photograph. But an adult brain changes only 0:14:00.600 --> 0:14:03.200 little bits at a time. It keeps most of its 0:14:03.240 --> 0:14:07.560 connections locked into place to hold on to what has 0:14:07.679 --> 0:14:12.760 been learned, and only small areas are made flexible via 0:14:12.880 --> 0:14:17.360 a combination lock of the right neurotransmitters. So an adult 0:14:17.440 --> 0:14:22.120 brain is like a point to list artist who modifies 0:14:22.240 --> 0:14:25.920 the color of only a few dots in an almost 0:14:26.120 --> 0:14:31.320 finished painting. Now you might wonder what does it feel 0:14:31.360 --> 0:14:36.160 like to be inside the massively flexible brain of a baby. 0:14:36.360 --> 0:14:39.080 I mean, we were all there as infants, but we 0:14:39.160 --> 0:14:42.360 can't remember that. So what is it like to be 0:14:42.440 --> 0:14:48.280 so plastic, so uninhibited and learning about a wide range 0:14:48.320 --> 0:14:52.040 of novel events. Well, you can probably get close to 0:14:52.200 --> 0:14:57.800 understanding it by considering other situations in your life in 0:14:57.840 --> 0:15:03.680 which your awareness plasticity are firing on all cylinders. So 0:15:04.000 --> 0:15:07.680 when you are traveling in a new land. You drink 0:15:07.720 --> 0:15:11.160 in all the sights and sounds and smells of the 0:15:11.280 --> 0:15:17.720 foreign country. You are experiencing lots of novelty and more 0:15:17.960 --> 0:15:24.200 learning and more distributed attention. After all, at home, you 0:15:24.240 --> 0:15:27.000 don't pay much attention to much of anything going on. 0:15:27.280 --> 0:15:30.760 Why because it's predictable. You know what to expect there. 0:15:31.280 --> 0:15:35.600 But when you're the traveler, you overflow with attention and 0:15:35.640 --> 0:15:40.040 your brain is changing much more. So think about it 0:15:40.080 --> 0:15:43.560 like this. When you are highly engaged and paying attention, 0:15:44.080 --> 0:15:48.480 you are like a baby again. So the difference is 0:15:48.560 --> 0:15:53.480 between a baby's very fluid brain and an adult's crystallized brain. 0:15:53.560 --> 0:15:56.760 This is easy to into it, but the neural transition 0:15:57.440 --> 0:16:03.560 from one to the other does happened in a smooth line. Instead, 0:16:03.960 --> 0:16:08.200 it's like a door that swings closed and once it shuts, 0:16:09.080 --> 0:16:12.800 large scale change is over. And this is the concept 0:16:13.200 --> 0:16:17.600 of this sensitive period. So to understand the sensitive period, 0:16:18.200 --> 0:16:22.640 consider an infant named Matthew, who is from my hometown. 0:16:23.040 --> 0:16:27.280 He started having epileptic seizures as a very young boy, 0:16:27.320 --> 0:16:30.480 and by the time he was six, these seizures were 0:16:30.520 --> 0:16:35.800 happening with increasing frequency, so he could be having multiple 0:16:35.880 --> 0:16:39.720 seizures in an hour, and his parents tried everything they 0:16:39.760 --> 0:16:41.760 could do to figure out what is going on here, 0:16:41.760 --> 0:16:44.480 and they finally found out that he had something called 0:16:44.960 --> 0:16:50.000 Rasmussen's encephalitis, which is an inflammation that affects an entire 0:16:50.280 --> 0:16:53.960 half of his brain. And so they searched everywhere for 0:16:54.000 --> 0:16:57.080 a solution, and they came to find out that really 0:16:57.160 --> 0:17:03.800 the only solution is a radical neurosurgery called a hemispherectomy. 0:17:03.880 --> 0:17:08.119 And in this surgery, an entire half of the brain 0:17:08.520 --> 0:17:12.600 is removed, just taken out, and that empty half of 0:17:12.640 --> 0:17:16.240 the skull fills up with cerebra spinal fluid, and if 0:17:16.240 --> 0:17:19.640 you do brain imaging, what you see is just blackness 0:17:19.720 --> 0:17:23.080 in that half of the head. Now, this is a 0:17:23.160 --> 0:17:26.000 horrifying thing for a parent to put their child through. 0:17:26.280 --> 0:17:29.840 But the completely amazing thing is that kids who get 0:17:29.840 --> 0:17:34.360 the surgery generally turn out to be just fine. They 0:17:34.400 --> 0:17:37.480 sometimes have a slight limp on the other side of 0:17:37.520 --> 0:17:39.760 their body because the left side of the body is 0:17:39.800 --> 0:17:42.280 controlled by the right side of the brain and vice versa, 0:17:42.400 --> 0:17:45.240 but other than that, they don't have any particular signs 0:17:45.280 --> 0:17:48.600 that tell anyone that they only have half of their 0:17:48.640 --> 0:18:07.920 brain remaining. Now I'm going to talk more about hemispherectomy 0:18:08.000 --> 0:18:09.760 is in a future episode. But the thing I want 0:18:09.760 --> 0:18:13.600 to emphasize here is that this kind of surgery is 0:18:13.960 --> 0:18:17.520 recommended only if the patient is less than let's say 0:18:17.600 --> 0:18:20.960 eight years old. Matthew was six when he went under 0:18:21.000 --> 0:18:24.160 the knife, which is nearing old age for this surgery. 0:18:24.480 --> 0:18:28.159 If a child is older, let's say an adolescent, he 0:18:28.240 --> 0:18:31.720 will have to function in life by bending tasks to 0:18:31.800 --> 0:18:35.320 fit what his brain can do, rather than counting on 0:18:35.400 --> 0:18:39.960 his brain to adapt to the tasks. So the thing 0:18:40.040 --> 0:18:42.600 to note here is that there is a door that 0:18:42.720 --> 0:18:46.320 closes at about eight years old, where your brain before 0:18:46.359 --> 0:18:49.040 that is so flexible that even if it only has 0:18:49.560 --> 0:18:53.600 half the real estate available, it can readjust to take 0:18:53.640 --> 0:18:57.280 care of all the functions that it needs. Before eight, 0:18:57.359 --> 0:19:02.680 you're fine. After probably not so fine now. This kind 0:19:02.680 --> 0:19:06.200 of age limit. This is seen in so many aspects 0:19:06.240 --> 0:19:11.240 of brain function. For example, sometimes there are heartbreaking cases 0:19:11.359 --> 0:19:15.359 in which a child is so profoundly neglected through her 0:19:15.480 --> 0:19:20.280 childhood without conversation and affection that she will end up 0:19:20.520 --> 0:19:25.040 incapable of speech. And if that child is found after 0:19:25.240 --> 0:19:28.359 a certain age, let's say about seven, she will be 0:19:28.680 --> 0:19:33.240 incapable of ever learning speech. Even when a team of 0:19:33.320 --> 0:19:37.399 psychologists come in and work with her for years to 0:19:37.560 --> 0:19:41.160 try to teach her language, it's too late. I told 0:19:41.200 --> 0:19:44.480 the story of one such girl, Danielle, in my book 0:19:44.520 --> 0:19:47.280 Live Wired, and I'll return to her story in a 0:19:47.359 --> 0:19:49.520 future episode. But the thing I want to emphasize for 0:19:49.600 --> 0:19:54.320 today is that the door for learning language closes. And 0:19:54.359 --> 0:19:57.320 I'm not talking about learning a second language or dealing 0:19:57.359 --> 0:19:59.439 with an accent or something like that. I'm talking about 0:19:59.640 --> 0:20:04.560 the idea of language. What language is, as in, how 0:20:04.600 --> 0:20:07.919 do I put words together to label things in the 0:20:07.920 --> 0:20:11.800 outside world and communicate with someone else this way, with 0:20:11.880 --> 0:20:16.680 a particular grammar and sentence structure and so on. If 0:20:16.720 --> 0:20:21.000 a child does not get language in the formative years, 0:20:21.600 --> 0:20:28.800 it becomes too late. Her maps have largely stabilized into 0:20:29.000 --> 0:20:33.159 place and they can't be changed anymore. So children like 0:20:33.560 --> 0:20:36.840 Matthew who got a hemisphectomy, or a child like Danielle 0:20:36.920 --> 0:20:40.320 who didn't get language in time, they tell the same story, 0:20:40.359 --> 0:20:43.920 which is that brains are really flexible at the beginning 0:20:44.400 --> 0:20:47.280 in this window of time known as the sensitive period, 0:20:47.720 --> 0:20:52.480 and as this period passes, the neural geography becomes more 0:20:52.600 --> 0:20:57.879 difficult to change. So as seen with children like Danielle, 0:20:58.119 --> 0:21:03.080 a young child's brain needs to hear lots of language 0:21:03.160 --> 0:21:07.240 during the sensitive period, and without that input, the neurons 0:21:07.320 --> 0:21:12.600 don't arrange themselves to capture the fundamental concepts of language. 0:21:13.359 --> 0:21:14.880 And by the way, it's a side note, you might 0:21:14.920 --> 0:21:18.879 wonder what happens with a deaf baby who doesn't hear 0:21:19.240 --> 0:21:23.320 any auditory input, and the answer is, as long as 0:21:23.359 --> 0:21:27.280 the parents present sign language to the baby, her brain 0:21:27.320 --> 0:21:32.040 will wire up correctly for communication. The deaf baby will 0:21:32.320 --> 0:21:38.080 employ her hands to babble, making resemblances to sign language, 0:21:38.080 --> 0:21:40.399 and the same way that a hearing baby exposed to 0:21:40.480 --> 0:21:44.199 language will babble with her vocal cords. If there is 0:21:44.400 --> 0:21:47.040 input to pick up on, the baby will do so. 0:21:47.880 --> 0:21:51.560 As long as that input arrives within the sensitive period. 0:21:51.960 --> 0:21:55.840 After that door swing shut, it's too late to learn 0:21:55.880 --> 0:22:01.720 the fundamentals of communication. So there's a window for acquiring 0:22:01.800 --> 0:22:05.119 the ability to communicate, and there are also windows for 0:22:05.320 --> 0:22:10.239 more subtle aspects of language, like accents. So take the 0:22:10.320 --> 0:22:15.480 actress Mila Kunis. She speaks American English with no discernible accent, 0:22:16.200 --> 0:22:18.600 so you probably didn't know that she was born in 0:22:18.800 --> 0:22:22.480 Ukraine and lived there, not speaking a word of English 0:22:22.600 --> 0:22:27.280 until the age of seven. Now, in contrast, Arnold Schwarzenegger, 0:22:27.640 --> 0:22:31.399 who's been in American filmmaking since his early twenties, he 0:22:31.480 --> 0:22:35.240 has a very strong Austrian accent. Why because he didn't 0:22:35.280 --> 0:22:37.719 move to America until he was twenty one, and that 0:22:37.920 --> 0:22:43.600 meant his use of English began too late. Brain wise, generally, 0:22:44.200 --> 0:22:47.040 if you arrive in a new country during your first 0:22:47.080 --> 0:22:51.000 seven years, your fluency in the new tongue will be 0:22:51.040 --> 0:22:54.199 as high as a native speakers, because your window of 0:22:54.240 --> 0:22:59.159 sensitivity for obtaining the sounds that's still open. If you 0:22:59.480 --> 0:23:02.280 immigrate when you're eight to ten years old, you have 0:23:02.320 --> 0:23:05.639 a slightly more difficult time blending in, but you'll be close. 0:23:06.080 --> 0:23:09.399 If you're past your teen years. When you move like 0:23:09.600 --> 0:23:13.479 Arnold was, your fluency is likely to remain low, and 0:23:13.480 --> 0:23:17.240 you're going to have an accent that reveals your history. 0:23:17.560 --> 0:23:21.920 So your ability to sonically morph into a different culture 0:23:22.640 --> 0:23:25.880 is a door that remains open for only about a decade. 0:23:27.000 --> 0:23:29.960 And let's take another example. Take something like vision. So 0:23:30.400 --> 0:23:35.160 imagine a child is born with misaligned eyes where one 0:23:35.200 --> 0:23:38.800 eye is pointing straight but the other eye points inwarder outward. 0:23:38.840 --> 0:23:42.520 This is known as strabismus, and colloquially it's often called 0:23:42.840 --> 0:23:46.040 being cross eyed or walleyed. What you do clinically is 0:23:46.080 --> 0:23:49.440 you fix the extra ocular muscles so the eyes can 0:23:49.520 --> 0:23:53.160 point the same direction, and then you cover the good 0:23:53.200 --> 0:23:56.000 eye for a while, which allows the weak eye to 0:23:56.600 --> 0:24:00.600 fight to regain its lost territory. But no out that 0:24:00.680 --> 0:24:03.000 the good eye has to be patched. You have to 0:24:03.080 --> 0:24:07.160 do this technique within this sensitive period about the first 0:24:07.280 --> 0:24:11.520 six years, otherwise it's too late. The vision will never 0:24:11.600 --> 0:24:16.280 be recoverable after that from the weakey. After six years, 0:24:16.320 --> 0:24:19.800 the dirt roads in the brain have been paved into 0:24:19.880 --> 0:24:24.760 highways and you can't now modify them. So this influence 0:24:25.080 --> 0:24:28.879 of developmental timing. You see this across all the senses. 0:24:29.680 --> 0:24:32.960 I talked in earlier episodes about how the body maps 0:24:33.080 --> 0:24:37.560 readjust if you have an amputation or when you learn 0:24:37.600 --> 0:24:41.920 a new musical instrument, but across the board, these kinds 0:24:41.960 --> 0:24:46.080 of changes happen more in young brains than in old brains, 0:24:47.160 --> 0:24:50.840 just like Mila Kunis with her unaccented speech. So we 0:24:51.000 --> 0:24:54.199 find that Jitzak Peerlman took up the violin at a 0:24:54.320 --> 0:24:56.840 very young age. If you were to take up the 0:24:56.960 --> 0:25:00.600 violin for the first time in your teenage years, there's 0:25:00.720 --> 0:25:04.720 no possibility that you would ever become a pearlman. Even 0:25:04.760 --> 0:25:07.840 if you worked really hard to rack up the same 0:25:07.920 --> 0:25:12.040 number of hours of practice. Your brain is already behind 0:25:12.080 --> 0:25:16.000 in the race. It has grown too solidified by the 0:25:16.040 --> 0:25:19.399 time you start doing your first piscata as a teenager. 0:25:20.560 --> 0:25:25.840 So acquiring vision and language and violin proficiency, this all 0:25:25.880 --> 0:25:29.680 depends on input from the world, and if a severely 0:25:29.800 --> 0:25:34.880 neglected child like Danielle doesn't receive this input, she can't 0:25:35.200 --> 0:25:39.280 later the ability to learn language, to possess vision, to 0:25:39.840 --> 0:25:44.040 interact socially, to walk normally, to have normal neurodevelopment. This 0:25:44.160 --> 0:25:47.600 is all limited to the years of young childhood, and 0:25:47.680 --> 0:25:52.159 after a certain point these abilities are lost. The brain 0:25:52.680 --> 0:25:56.400 needs to experience the proper input within the right window 0:25:56.880 --> 0:26:02.320 to achieve its most useful connectivity. Now, as a result 0:26:02.440 --> 0:26:06.840 of this diminishing flexibility, we are highly influenced by the 0:26:06.880 --> 0:26:10.400 events that happen in our childhoods. So here's a really 0:26:10.400 --> 0:26:15.560 interesting example. Consider the correlation between how tall a man 0:26:15.840 --> 0:26:20.600 is and how much salary he will command. In America, 0:26:21.000 --> 0:26:25.080 each additional inch of height translates into a one point 0:26:25.119 --> 0:26:29.920 eight percent increase in take home pay. Why is that well, 0:26:30.240 --> 0:26:34.199 the popular assumption is that this stems from discrimination in 0:26:34.280 --> 0:26:38.040 hiring practices. Everyone wants to hire the tall guy because 0:26:38.040 --> 0:26:41.200 of his commanding presence. But it turns out there is 0:26:41.720 --> 0:26:46.600 a deeper reason. The best indicator of a male's future 0:26:46.680 --> 0:26:52.479 salary is how tall he was at the age of sixteen. However, 0:26:52.520 --> 0:26:55.800 tall he grows after that doesn't change the outcome. Now, 0:26:55.800 --> 0:26:59.080 how do we understand that? Could it be some effect 0:26:59.119 --> 0:27:03.920 of nutritional differences between people? Know because when the researchers 0:27:04.000 --> 0:27:08.240 correlated with height at ages seven or eleven, the effect 0:27:08.320 --> 0:27:13.160 wasn't as strong. Instead, it's that the teenage years are 0:27:13.200 --> 0:27:17.439 a time when social status is being worked out, and 0:27:17.520 --> 0:27:21.600 as a result, who you are as an adult strongly 0:27:21.640 --> 0:27:26.119 depends on who you were then. In fact, studies that 0:27:26.240 --> 0:27:31.320 track thousands of children into adulthood find that socially oriented 0:27:31.359 --> 0:27:35.520 careers like sales or managing other people show the strongest 0:27:35.560 --> 0:27:39.240 effect of teenage height, and other careers like blue collar 0:27:39.280 --> 0:27:44.800 work or artistic trades are less influenced. So how people 0:27:44.920 --> 0:27:49.680 treat you during your formative years has an enormous impact. 0:27:49.800 --> 0:27:53.240 On your comportment in the world in terms of self 0:27:53.320 --> 0:27:57.679 esteem and confidence and leadership. Here's another example. Think about 0:27:58.200 --> 0:28:00.880 Oprah Winfrey, who is worth the bid two point eight 0:28:01.000 --> 0:28:04.320 billion dollars. So I was a little surprised when I 0:28:04.400 --> 0:28:08.440 read that she has a deep rooted fear of ending 0:28:08.520 --> 0:28:12.840 up homeless and penniless. But it's because of the path 0:28:13.119 --> 0:28:16.840 that got her here. Before she was an empress of 0:28:16.880 --> 0:28:20.840 the media, she was an impoverished child in Mississippi. She 0:28:20.920 --> 0:28:25.000 was born to a teenage single mother. So who she 0:28:25.440 --> 0:28:30.879 was then influenced who she is now. The Great Aristotle 0:28:31.119 --> 0:28:33.959 noted this twenty four hundred years ago. He said, quote, 0:28:34.240 --> 0:28:38.960 the habits we form from childhood make no small difference, 0:28:39.320 --> 0:28:44.840 but rather they make all the difference. Okay, So to 0:28:45.000 --> 0:28:49.440 capture the idea of the sensitive period, I introduced the 0:28:49.480 --> 0:28:52.800 metaphor of a door swinging shut. But now we're ready 0:28:52.840 --> 0:28:55.800 to take the analogy to the next level. It's not 0:28:56.360 --> 0:29:00.080 one door, it's a bunch of different doors which swing 0:29:00.160 --> 0:29:04.360 shut at different times. So let's look at an example 0:29:04.400 --> 0:29:07.440 of that. Sometimes the brain is so impressionable in its 0:29:07.520 --> 0:29:10.120 earliest days that it can sometimes get into hot water. 0:29:10.480 --> 0:29:15.680 For example, the baby goose hatches from its egg, and 0:29:15.720 --> 0:29:20.960 it establishes a parental relationship with the first animate object 0:29:21.040 --> 0:29:24.280 that it sees. And this is a sufficient strategy in 0:29:24.320 --> 0:29:27.920