years ago it was widely assumed that the vast majority of brain development takes place in the first few years of life back then fifteen years ago we didn 't have the ability to look inside the living human brain and track development across the lifespan
if you 'd like to take a snapshot a photograph at really high resolution of the inside of the living human brain and we can ask questions like how much gray matter does the brain contain and how does that change with age
so many labs around the world are involved in this kind of research and we now have a really rich and detailed picture of how the living human brain develops and this picture has radically changed the way we think about human brain development
by revealing that it 's not all over in early childhood and instead the brain continues to develop right throughout
one of the brain regions that changes most dramatically during adolescence is called prefrontal cortex
prefrontal cortex is an interesting brain area it 's proportionally much bigger in humans than in any other species and it 's involved in a whole range of high level cognitive functions things like decision making planning planning what you 're going to do tomorrow or next week or next year
inhibiting inappropriate behavior so stopping yourself saying something really rude or doing something really stupid it 's also involved in social interaction understanding other people and self awareness
so mri studies looking at the development of this region have shown that it really undergoes dramatic development during the period of adolescence
so if you look at gray matter volume for example gray matter volume across age from age four to twenty two years increases during childhood which is what you can see on this graph it peaks in early adolescence the arrows indicate peak gray matter volume in prefrontal cortex
you can see that that peak happens a couple of years later
in boys relative to girls and that 's probably because boys go through puberty a couple of years later than girls on average and then during adolescence there 's a significant decline in gray matter volume in prefrontal cortex now that might sound bad but actually this is a really important developmental process
and this decline in gray matter volume during prefrontal cortex
is thought to correspond to synaptic pruning the elimination of unwanted synapses this is a really important process it 's partlydependent on the environment that the animal or the human is in and the synapses that are being used are strengthened
and synapses that aren 't being used in that particular environment are pruned away you can think of it a bit like pruning a rosebush you prune away the weaker branches so that the remaining important branches
brain tissue according to the speciesspecificenvironment is happening in prefrontal cortex and in other brain regions during the period of human adolescence
so a second line of inquiry that we use to track changes in the adolescent brain is using functional mri to look at changes in brain activity across age so i 'll just give you an example from my lab so in my
of how your social brains work
so this is a soccer game laughter michael owen has just missed a goal and he 's lying on the ground and the first aspect of the social brain that this picture really nicely illustrates is how automatic and instinctive
social emotional responses are so within a split second of michael owen missing this goal everyone is doing the same thing with their arms and the same thing with their face even michael owen as he slides along the grass is doing the same thing with his arms and presumably has a similar facial expression and the only people who don 't are the guys in yellow at the back
of the social brain that this picture really nicely illustrates how good we are at reading other people 's behavior their actions their gestures their facial expressions in terms of their underlying emotions and mental states
so you don 't have to ask any of these guys you have a pretty good idea of what they 're feeling and thinking at this precise moment in time
that involves thinking about other people their minds their mental states their emotions and one of the findings that we 've found several times now as have other labs around the world is part of the prefrontal cortex called medial prefrontal cortex which is shown in blue on the slide and it 's right in the middle of prefrontal cortex in the midline of your head
this region is more active in adolescents when they make these social decisions and think about other people than it is in adults and this is actually a meta analysis of nine different studies in this area from labs around the world and they all show the same thing that activity in this medial prefrontal cortex area
decreases during the period of adolescence and we think that might be because adolescents and adults use a different mental approach a different cognitive strategy to make social decisions and one way of looking at that
this is the same set of shelves from his point of view notice that there are only some objects that he can see whereas there are many more objects that you can see
now your task is to move objects around the directorstanding behind the set of shelves is going to direct you to move objects around but remember he 's not going to ask you to move objects that he can 't see
this introduces a really interesting condition whereby there 's a kind of conflict between your perspective and the director 's perspective so imagine he tells you to move the top truck left
there are three trucks there you 're going to instinctively go for the white truck because that 's the top truck
from your perspective but then you have to remember oh he can 't see that truck so he must mean me to move the blue truck which is the top truck from his perspective now believe it or not normalhealthyintelligent adults like you make errors about fifty percent of the time on that kind of trial they move the white truck instead of the blue truck
okay so if i just show you the percentage errors in a large developmental study we did
this is in a study ranging from age seven to adulthood and what you 're going to see is the percentage errors in the adult group in both conditions
the gray is the director condition and you see that our intelligent adults are making errors about fifty percent of the time whereas they make far fewer errors when there 's no director present when they just have to remember that rule of ignoring the gray background
developmentally these two conditions develop in exactly the same way between late childhood and mid adolescence there 's an improvement in other words a reduction of errors in both of these trials in both of these conditions but it 's when you compare the last two groups the mid adolescent group and the adult group where things get really interesting because there
there is no continued improvement in the no director condition in other words everything you need
to do in order to remember the rule and apply it seems to be fully developed by mid adolescence whereas in contrast if you look at the last two gray bars
so if you have a teenage son or a daughter and you sometimes think they have problems taking other people 's perspectives you 're right they do and this is why so we sometimes
laugh about teenagers they 're parodied sometimes even demonized in the media
for their kind of typical teenage behavior they take risks they 're sometimes moody they 're very self conscious
i have a really nice anecdote from a friend of mine who said that
the thing he noticed most about his teenage daughters before and after puberty was their level of embarrassment in front of him so he said before puberty if my two daughters were messing around in a shop i 'd say hey stop messing around and i 'll sing your favorite song and instantly they 'd stop messing around and he 'd sing their favorite song after puberty that became the threat
there 's a famous quote by shakespeare from the winter 's tale where he describes adolescence as follows
i would there were no age between ten and three and twenty or that youth would sleep out the rest for there is nothing in the between but getting wenches with child wronging the ancientry stealing fighting
so for example take risk taking we know that adolescents have a tendency to take risks they do they take more risks than children or adults and they are particularly prone to taking risks when they 're with their friends there 's an important drive
to become independent from one 's parents and to impress one 's friends in adolescence but now we try to understand that in terms of the development of a part of their brain called the limbic system so i 'm going to show you the limbic system in red in the slide behind me and also on this brain so the limbic system is right
and this region the regions within the limbic system have been found to be hypersensitive to the rewarding feeling of risk taking in adolescents compared with adults and
so brain research has shown that the adolescent brain undergoes really quite profound development and this has implications for education
for rehabilitation and intervention the environment including teaching can and does shape the developing adolescent brain and yet it 's only relatively recently that we have been routinely educating teenagers in the west all four of my grandparents for example
left school in their early adolescence they had no choice and that 's still the case for many many teenagers around the world today forty percent of teenagers don 't have access to secondary school
education and yet this is a period of life where the brain is particularly adaptable and malleable it 's a fantastic opportunity for learning and creativity
so what 's sometimes seen as the problem with adolescents heightened risk taking poor impulse control self consciousness shouldn 't be stigmatized it actually reflects changes in the brain that provide an excellent opportunity for education and social development thank you
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