0:00:00.688,0:00:03.577 Fifteen years ago, it was widely assumed 0:00:03.577,0:00:05.627 that the vast majority of brain development 0:00:05.627,0:00:08.606 takes place in the first few years of life. 0:00:08.606,0:00:11.318 Back then, 15 years ago, we didn't have the ability 0:00:11.318,0:00:13.939 to look inside the living human brain 0:00:13.939,0:00:16.977 and track development across the lifespan. 0:00:16.977,0:00:20.138 In the past decade or so, mainly due to advances 0:00:20.138,0:00:21.943 in brain imaging technology 0:00:21.943,0:00:24.886 such as magnetic resonance imaging, or MRI, 0:00:24.886,0:00:28.013 neuroscientists have started to look inside the living 0:00:28.013,0:00:30.432 human brain of all ages, and to track changes 0:00:30.432,0:00:33.303 in brain structure and brain function, 0:00:33.303,0:00:36.980 so we use structural MRI if you'd like to take a snapshot, 0:00:36.980,0:00:40.042 a photograph, at really high resolution of the inside 0:00:40.042,0:00:43.262 of the living human brain, and we can ask questions like, 0:00:43.262,0:00:45.702 how much gray matter does the brain contain, 0:00:45.702,0:00:47.505 and how does that change with age? 0:00:47.505,0:00:51.217 And we also use functional MRI, called fMRI, 0:00:51.217,0:00:54.612 to take a video, a movie, of brain activity 0:00:54.612,0:00:57.480 when participants are taking part in some kind of task 0:00:57.480,0:01:00.372 like thinking or feeling or perceiving something. 0:01:00.372,0:01:03.138 So many labs around the world are involved in this kind 0:01:03.138,0:01:05.368 of research, and we now have a really rich 0:01:05.368,0:01:08.892 and detailed picture of how the living human brain develops, 0:01:08.892,0:01:11.960 and this picture has radically changed the way 0:01:11.960,0:01:14.593 we think about human brain development 0:01:14.593,0:01:17.361 by revealing that it's not all over in early childhood, 0:01:17.361,0:01:20.072 and instead, the brain continues to develop 0:01:20.072,0:01:24.118 right throughout adolescence and into the '20s and '30s. 0:01:24.118,0:01:28.097 So adolescence is defined as the period of life that starts 0:01:28.097,0:01:32.493 with the biological, hormonal, physical changes of puberty 0:01:32.493,0:01:35.778 and ends at the age at which an individual attains 0:01:35.778,0:01:39.229 a stable, independent role in society. 0:01:39.229,0:01:41.019 (Laughter) 0:01:41.019,0:01:43.784 It can go on a long time. (Laughter) 0:01:43.784,0:01:46.803 One of the brain regions that changes most dramatically 0:01:46.803,0:01:50.067 during adolescence is called prefrontal cortex. 0:01:50.067,0:01:53.044 So this is a model of the human brain, 0:01:53.044,0:01:55.924 and this is prefrontal cortex, right at the front. 0:01:55.924,0:01:58.433 Prefrontal cortex is an interesting brain area. 0:01:58.433,0:02:01.547 It's proportionally much bigger in humans than 0:02:01.547,0:02:05.174 in any other species, and it's involved in a whole range of 0:02:05.190,0:02:08.462 high level cognitive functions, things like decision-making, 0:02:08.462,0:02:10.552 planning, planning what you're going to do tomorrow 0:02:10.552,0:02:13.292 or next week or next year, inhibiting 0:02:13.292,0:02:15.958 inappropriate behavior, so stopping yourself saying 0:02:15.958,0:02:18.883 something really rude or doing something really stupid. 0:02:18.883,0:02:20.661 It's also involved in social interaction, 0:02:20.661,0:02:23.785 understanding other people, and self-awareness. 0:02:23.785,0:02:26.835 So MRI studies looking at the development of this region 0:02:26.835,0:02:29.305 have shown that it really undergoes dramatic development 0:02:29.305,0:02:32.238 during the period of adolescence. 0:02:32.238,0:02:35.196 So if you look at gray matter volume, for example, 0:02:35.196,0:02:40.045 gray matter volume across age from age four to 22 years 0:02:40.045,0:02:42.367 increases during childhood, which is what you can see 0:02:42.367,0:02:46.120 on this graph. It peaks in early adolescence. 0:02:46.120,0:02:48.685 The arrows indicate peak gray matter volume 0:02:48.685,0:02:52.151 in prefrontal cortex. You can see that that peak happens 0:02:52.151,0:02:55.661 a couple of years later in boys relative to girls, 0:02:55.661,0:02:57.500 and that's probably because boys go through puberty 0:02:57.500,0:02:59.752 a couple of years later than girls on average, 0:02:59.752,0:03:03.187 and then during adolescence, there's a significant decline 0:03:03.187,0:03:05.872 in gray matter volume in prefrontal cortex. 0:03:05.872,0:03:07.897 Now that might sound bad, but actually this is 0:03:07.897,0:03:11.047 a really important developmental process, because 0:03:11.047,0:03:15.153 gray matter contains cell bodies and connections 0:03:15.153,0:03:18.607 between cells, the synapses, and this decline 0:03:18.607,0:03:21.352 in gray matter volume during prefrontal cortex 0:03:21.352,0:03:24.244 is thought to correspond to synaptic pruning, 0:03:24.244,0:03:26.567 the elimination of unwanted synapses. 0:03:26.567,0:03:29.700 This is a really important process. It's partly dependent 0:03:29.700,0:03:32.834 on the environment that the animal or the human is in, 0:03:32.834,0:03:36.278 and the synapses that are being used are strengthened, 0:03:36.278,0:03:38.211 and synapses that aren't being used 0:03:38.211,0:03:40.543 in that particular environment are pruned away. 0:03:40.543,0:03:43.049 You can think of it a bit like pruning a rosebush. 0:03:43.049,0:03:45.889 You prune away the weaker branches so that 0:03:45.889,0:03:48.927 the remaining, important branches, can grow stronger, 0:03:48.927,0:03:52.853 and this process, which effectively fine-tunes brain tissue 0:03:52.853,0:03:55.520 according to the species-specific environment, 0:03:55.520,0:03:58.435 is happening in prefrontal cortex and in other brain regions 0:03:58.435,0:04:01.989 during the period of human adolescence. 0:04:01.989,0:04:05.690 So a second line of inquiry that we use to track changes 0:04:05.690,0:04:08.942 in the adolescent brain is using functional MRI 0:04:08.942,0:04:12.215 to look at changes in brain activity across age. 0:04:12.215,0:04:13.857 So I'll just give you an example from my lab. 0:04:13.857,0:04:17.418 So in my lab, we're interested in the social brain, that is 0:04:17.418,0:04:21.002 the network of brain regions that we use to understand 0:04:21.002,0:04:23.435 other people and to interact with other people. 0:04:23.435,0:04:27.201 So I like to show a photograph of a soccer game 0:04:27.201,0:04:31.608 to illustrate two aspects of how your social brains work. 0:04:31.608,0:04:33.041 So this is a soccer game. (Laughter) 0:04:33.041,0:04:35.683 Michael Owen has just missed a goal, and he's lying 0:04:35.683,0:04:38.485 on the ground, and the first aspect of the social brain 0:04:38.485,0:04:41.444 that this picture really nicely illustrates is how automatic 0:04:41.444,0:04:44.494 and instinctive social emotional responses are, 0:04:44.494,0:04:47.458 so within a split second of Michael Owen missing this goal, 0:04:47.458,0:04:49.268 everyone is doing the same thing with their arms 0:04:49.268,0:04:51.071 and the same thing with their face, even Michael Owen 0:04:51.071,0:04:52.895 as he slides along the grass, is doing the same thing 0:04:52.895,0:04:55.164 with his arms, and presumably has a similar 0:04:55.164,0:04:57.138 facial expression, and the only people who don't 0:04:57.138,0:05:00.599 are the guys in yellow at the back — (Laughs) — 0:05:00.599,0:05:03.142 and I think they're on the wrong end of the stadium, 0:05:03.142,0:05:05.437 and they're doing another social emotional response 0:05:05.437,0:05:08.072 that we all instantly recognize, and that's the second aspect 0:05:08.072,0:05:11.708 of the social brain that this picture really nicely illustrates, 0:05:11.708,0:05:15.090 how good we are at reading other people's behavior, 0:05:15.090,0:05:17.767 their actions, their gestures, their facial expressions, 0:05:17.767,0:05:21.583 in terms of their underlying emotions and mental states. 0:05:21.583,0:05:23.360 So you don't have to ask any of these guys. 0:05:23.360,0:05:25.901 You have a pretty good idea of what they're feeling 0:05:25.901,0:05:28.489 and thinking at this precise moment in time. 0:05:28.489,0:05:30.245 So that's what we're interested in looking at in my lab. 0:05:30.245,0:05:33.817 So in my lab, we bring adolescents and adults into the lab 0:05:33.833,0:05:36.218 to have a brain scan, we give them some kind of task 0:05:36.218,0:05:39.512 that involves thinking about other people, their minds, 0:05:39.512,0:05:42.406 their mental states, their emotions, and one of the findings 0:05:42.406,0:05:45.252 that we've found several times now, as have other labs 0:05:45.252,0:05:48.470 around the world, is part of the prefrontal cortex called 0:05:48.470,0:05:51.688 medial prefrontal cortex, which is shown in blue on the slide, 0:05:51.688,0:05:54.444 and it's right in the middle of prefrontal cortex 0:05:54.444,0:05:56.842 in the midline of your head. 0:05:56.842,0:06:00.125 This region is more active in adolescents when they make 0:06:00.125,0:06:02.252 these social decisions and think about other people 0:06:02.252,0:06:05.053 than it is in adults, and this is actually a meta-analysis 0:06:05.053,0:06:08.293 of nine different studies in this area from labs around 0:06:08.293,0:06:10.993 the world, and they all show the same thing, that activity 0:06:10.993,0:06:14.363 in this medial prefrontal cortex area decreases 0:06:14.363,0:06:16.810 during the period of adolescence. 0:06:16.810,0:06:19.454 And we think that might be because adolescents and adults 0:06:19.454,0:06:21.820 use a different mental approach, a different 0:06:21.820,0:06:25.238 cognitive strategy, to make social decisions, 0:06:25.238,0:06:28.754 and one way of looking at that is to do behavioral studies 0:06:28.754,0:06:30.731 whereby we bring people into the lab and we give them 0:06:30.731,0:06:33.275 some kind of behavioral task, and I'll just give you 0:06:33.275,0:06:36.485 another example of the kind of task that we use in my lab. 0:06:36.485,0:06:39.133 So imagine that you're the participant in one of our 0:06:39.133,0:06:40.858 experiments. You come into the lab, 0:06:40.858,0:06:43.532 you see this computerized task. 0:06:43.532,0:06:46.322 In this task, you see a set of shelves. 0:06:46.322,0:06:49.139 Now, there are objects on these shelves, on some of them, 0:06:49.139,0:06:52.110 and you'll notice there's a guy standing behind the set 0:06:52.110,0:06:55.695 of shelves, and there are some objects that he can't see. 0:06:55.695,0:06:57.974 They're occluded, from his point of view, with a kind of 0:06:57.974,0:07:00.618 gray piece of wood. 0:07:00.618,0:07:04.102 This is the same set of shelves from his point of view. 0:07:04.102,0:07:07.595 Notice that there are only some objects that he can see, 0:07:07.595,0:07:10.047 whereas there are many more objects that you can see. 0:07:10.047,0:07:12.243 Now your task is to move objects around. 0:07:12.243,0:07:14.605 The director, standing behind the set of shelves, 0:07:14.605,0:07:17.350 is going to direct you to move objects around, 0:07:17.350,0:07:19.244 but remember, he's not going to ask you to move objects 0:07:19.244,0:07:22.964 that he can't see. This introduces a really interesting 0:07:22.964,0:07:25.157 condition whereby there's a kind of conflict 0:07:25.157,0:07:28.325 between your perspective and the director's perspective. 0:07:28.325,0:07:31.565 So imagine he tells you to move the top truck left. 0:07:31.565,0:07:33.596 There are three trucks there. You're going to instinctively 0:07:33.611,0:07:35.761 go for the white truck, because that's the top truck 0:07:35.761,0:07:38.579 from your perspective, but then you have to remember, 0:07:38.579,0:07:40.638 "Oh, he can't see that truck, so he must mean 0:07:40.638,0:07:43.395 me to move the blue truck," which is the top truck 0:07:43.395,0:07:46.040 from his perspective. Now believe it or not, 0:07:46.040,0:07:48.991 normal, healthy, intelligent adults like you make errors 0:07:48.991,0:07:52.131 about 50 percent of the time on that kind of trial. 0:07:52.131,0:07:54.974 They move the white truck instead of the blue truck. 0:07:54.974,0:07:58.290 So we give this kind of task to adolescents and adults, 0:07:58.290,0:07:59.844 and we also have a control condition 0:07:59.844,0:08:03.905 where there's no director and instead we give people a rule. 0:08:03.905,0:08:05.819 We tell them, okay, we're going to do exactly the same thing 0:08:05.819,0:08:08.656 but this time there's no director. Instead you've got to 0:08:08.656,0:08:11.863 ignore objects with the dark gray background. 0:08:11.863,0:08:14.563 You'll see that this is exactly the same condition, only 0:08:14.563,0:08:17.409 in the no-director condition they just have to remember 0:08:17.409,0:08:20.480 to apply this somewhat arbitrary rule, whereas 0:08:20.480,0:08:22.160 in the director condition, they have to remember 0:08:22.160,0:08:25.701 to take into account the director's perspective 0:08:25.701,0:08:29.998 in order to guide their ongoing behavior. 0:08:29.998,0:08:32.608 Okay, so if I just show you the percentage errors 0:08:32.608,0:08:35.174 in a large developmental study we did, 0:08:35.174,0:08:38.728 this is in a study ranging from age seven to adulthood, 0:08:38.728,0:08:39.938 and what you're going to see is the percentage errors 0:08:39.938,0:08:41.912 in the adult group in both conditions, 0:08:41.927,0:08:45.198 so the gray is the director condition, and you see 0:08:45.198,0:08:47.771 that our intelligent adults are making errors about 50 percent 0:08:47.771,0:08:50.486 of the time, whereas they make far fewer errors 0:08:50.486,0:08:52.514 when there's no director present, when they just have 0:08:52.514,0:08:55.595 to remember that rule of ignoring the gray background. 0:08:55.595,0:08:58.263 Developmentally, these two conditions develop 0:08:58.263,0:09:01.186 in exactly the same way. Between late childhood 0:09:01.186,0:09:03.427 and mid-adolescence, there's an improvement, 0:09:03.427,0:09:06.778 in other words a reduction of errors, in both of these trials, 0:09:06.778,0:09:07.898 in both of these conditions. 0:09:07.898,0:09:10.183 But it's when you compare the last two groups, 0:09:10.183,0:09:12.135 the mid-adolescent group and the adult group 0:09:12.135,0:09:15.295 where things get really interesting, because there, there is 0:09:15.295,0:09:18.333 no continued improvement in the no-director condition. 0:09:18.333,0:09:21.263 In other words, everything you need to do in order to 0:09:21.263,0:09:23.969 remember the rule and apply it seems to be fully developed 0:09:23.969,0:09:26.500 by mid-adolescence, whereas in contrast, 0:09:26.500,0:09:28.897 if you look at the last two gray bars, there's still 0:09:28.897,0:09:32.047 a significant improvement in the director condition 0:09:32.047,0:09:34.488 between mid-adolescence and adulthood, and what 0:09:34.488,0:09:37.864 this means is that the ability to take into account someone 0:09:37.864,0:09:41.149 else's perspective in order to guide ongoing behavior, 0:09:41.149,0:09:43.408 which is something, by the way, that we do in everyday life all 0:09:43.408,0:09:48.014 the time, is still developing in mid-to-late adolescence. 0:09:48.014,0:09:50.554 So if you have a teenage son or a daughter and you 0:09:50.554,0:09:52.963 sometimes think they have problems taking other people's 0:09:52.963,0:09:56.719 perspectives, you're right. They do. And this is why. 0:09:56.719,0:10:00.232 So we sometimes laugh about teenagers. 0:10:00.232,0:10:04.095 They're parodied, sometimes even demonized in the media 0:10:04.095,0:10:07.622 for their kind of typical teenage behavior. They take risks, 0:10:07.622,0:10:10.393 they're sometimes moody, they're very self-conscious. 0:10:10.393,0:10:12.886 I have a really nice anecdote from a friend of mine 0:10:12.886,0:10:15.373 who said that the thing he noticed most 0:10:15.373,0:10:18.354 about his teenage daughters before and after puberty 0:10:18.354,0:10:20.598 was their level of embarrassment in front of him. 0:10:20.614,0:10:23.103 So, he said, "Before puberty, if my two daughters 0:10:23.103,0:10:25.357 were messing around in a shop, I'd say, 'Hey, 0:10:25.357,0:10:27.106 stop messing around and I'll sing your favorite song,' 0:10:27.106,0:10:29.007 and instantly they'd stop messing around and he'd sing 0:10:29.007,0:10:32.478 their favorite song. After puberty, that became the threat. 0:10:32.478,0:10:34.295 (Laughter) 0:10:34.295,0:10:37.772 The very notion of their dad singing in public 0:10:37.772,0:10:40.135 was enough to make them behave. 0:10:40.135,0:10:41.563 So people often ask, 0:10:41.563,0:10:44.196 "Well, is adolescence a kind of recent phenomenon? 0:10:44.196,0:10:46.318 Is it something we've invented recently in the West?" 0:10:46.318,0:10:48.986 And actually, the answer is probably not. There are lots 0:10:48.986,0:10:52.409 of descriptions of adolescence in history that sound 0:10:52.409,0:10:54.566 very similar to the descriptions we use today. 0:10:54.566,0:10:58.799 So there's a famous quote by Shakespeare from "The Winter's Tale" 0:10:58.799,0:11:01.574 where he describes adolescence as follows: 0:11:01.574,0:11:04.420 "I would there were no age between ten and 0:11:04.420,0:11:07.660 three-and-twenty, or that youth would sleep out the rest; 0:11:07.660,0:11:09.751 for there is nothing in the between but getting wenches 0:11:09.751,0:11:15.974 with child, wronging the ancientry, stealing, fighting." (Laughter) 0:11:15.974,0:11:20.508 He then goes on to say, "Having said that, would any 0:11:20.508,0:11:23.653 but these boiled brains of nineteen and two-and-twenty 0:11:23.653,0:11:26.151 hunt in this weather?" (Laughter) 0:11:26.151,0:11:29.077 So almost 400 years ago, Shakespeare was portraying 0:11:29.077,0:11:31.801 adolescents in a very similar light to the light that we 0:11:31.801,0:11:35.260 portray them in today, but today we try to understand 0:11:35.260,0:11:38.347 their behavior in terms of the underlying changes 0:11:38.347,0:11:40.285 that are going on in their brain. 0:11:40.285,0:11:43.893 So for example, take risk-taking. We know that adolescents 0:11:43.893,0:11:46.218 have a tendency to take risks. They do. 0:11:46.218,0:11:48.850 They take more risks than children or adults, 0:11:48.850,0:11:51.310 and they are particularly prone to taking risks 0:11:51.310,0:11:54.278 when they're with their friends. There's an important drive 0:11:54.278,0:11:56.764 to become independent from one's parents 0:11:56.764,0:11:59.588 and to impress one's friends in adolescence. 0:11:59.588,0:12:02.187 But now we try to understand that in terms of 0:12:02.187,0:12:05.180 the development of a part of their brain called the limbic system, 0:12:05.180,0:12:07.723 so I'm going to show you the limbic system in red 0:12:07.723,0:12:09.588 in the slide behind me, and also on this brain. 0:12:09.588,0:12:12.697 So the limbic system is right deep inside the brain, 0:12:12.697,0:12:16.430 and it's involved in things like emotion processing 0:12:16.430,0:12:19.580 and reward processing. It gives you the rewarding feeling 0:12:19.580,0:12:22.876 out of doing fun things, including taking risks. 0:12:22.876,0:12:25.241 It gives you the kick out of taking risks. 0:12:25.241,0:12:28.289 And this region, the regions within the limbic system, 0:12:28.289,0:12:31.708 have been found to be hypersensitive to the rewarding 0:12:31.708,0:12:35.477 feeling of risk-taking in adolescents compared with adults, 0:12:35.477,0:12:39.179 and at the very same time, the prefrontal cortex, 0:12:39.179,0:12:41.453 which you can see in blue in the slide here, 0:12:41.453,0:12:44.320 which stops us taking excessive risks, 0:12:44.320,0:12:47.718 is still very much in development in adolescents. 0:12:47.718,0:12:51.385 So brain research has shown that the adolescent brain 0:12:51.385,0:12:54.727 undergoes really quite profound development, 0:12:54.727,0:12:58.683 and this has implications for education, for rehabilitation, 0:12:58.683,0:13:02.703 and intervention. The environment, including teaching, 0:13:02.703,0:13:06.112 can and does shape the developing adolescent brain, 0:13:06.112,0:13:08.914 and yet it's only relatively recently that we have been 0:13:08.914,0:13:11.419 routinely educating teenagers in the West. 0:13:11.419,0:13:15.172 All four of my grandparents, for example, left school 0:13:15.172,0:13:19.006 in their early adolescence. They had no choice. 0:13:19.006,0:13:21.780 And that's still the case for many, many teenagers 0:13:21.780,0:13:24.947 around the world today. Forty percent of teenagers 0:13:24.947,0:13:29.169 don't have access to secondary school education. 0:13:29.169,0:13:31.808 And yet, this is a period of life where the brain is 0:13:31.808,0:13:34.655 particularly adaptable and malleable. 0:13:34.655,0:13:38.425 It's a fantastic opportunity for learning and creativity. 0:13:38.425,0:13:40.658 So what's sometimes seen as the problem 0:13:40.658,0:13:43.134 with adolescents — heightened risk-taking, poor impulse 0:13:43.134,0:13:47.076 control, self-consciousness — shouldn't be stigmatized. 0:13:47.076,0:13:49.913 It actually reflects changes in the brain that provide 0:13:49.913,0:13:52.827 an excellent opportunity for education 0:13:52.827,0:13:57.257 and social development. Thank you. (Applause) 0:13:57.257,0:14:05.027 (Applause)