The mysterious workings of the adolescent brain SarahJayne Blakemore

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fifteen years ago it was widely assumed

that the vast majority of brain

development takes place in the first few

years of life back then 15 years ago we

didn’t have the ability to look inside

the living human brain and track

development across the lifespan in the

past decade or so mainly due to advances

in brain imaging technology such as

magnetic resonance imaging or MRI

neuroscientists have started to look

inside the living human brain of all

ages and to track changes in brain

structure and brain function so we use

structural MRI if you like to take a

snapshot of 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 and we also use functional MRI

called fMRI to take a video a movie of

brain activity and participants are

taking part in some kind of task like

thinking or feeling or perceiving

something 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

adolescence and into the 20s and 30s

so adolescence is defined as the period

of life that starts with the biological

hormonal physical changes of puberty and

ends at the age at which an individual

attains a stable independent role in

society it can go on a long time

one of the brain regions that changes

most dramatically during adolescence is

called prefrontal cortex so this is this

is a model of the human brain and this

is prefrontal cortex right at the front

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

because gray matter contains cell bodies

and connections between cells the

synapses and this decline in gray matter

volume during prefrontal cortex is

thought to correspond to synaptic

pruning the elimination of unwanted

signups –is this is a really important

process it’s partly dependent on the

environment that the animal or the human

is in in that sign APS’s that are being

used are strengthened and sign APS’s

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 can grow stronger and this

process which effectively fine-tunes

brain tissue according to the species

specific environment

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 lab we’re

interested in the social brain that is

the network of brain regions that we use

to understand other people and to

interact with other people so I like to

show a photograph of a soccer game to

illustrate two aspects of how your

social brains work so this is a soccer

game 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 Mike roan as he

slides along the grass is doing the same

thing through disarms and presumably has

a similar facial expression and the only

people who don’t are the guys in yellow

at the back a nice I think they’re on

the wrong end of the stadium and they’re

doing another social emotional response

that we all instantly recognize and

that’s the second aspect of the social

brain that this picture really nicely

illustrates how good we are 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

so that’s what we’re interested in

looking at in my lab we in my lab we

bring adolescents and adults into the

lab to have a brain scan we give them

some kind of task that involves thinking

about other people their minds their

mental states their emotions and one of

the findings that we 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 um right

in the middle of prefrontal cortex and

then 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 showed 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

is to do behavioral studies whereby we

bring people into the lab and we give

them some kind of behavioral task and

I’ll just give you another example of

the kind of task that we use in my lab

so imagine that you’re the participant

in one of our experiments you come to

the lab you see this computerized task

in this task you see a set of shelves

now there are objects on these shelves

on some of them and you’ll notice

there’s a guy standing behind the set of

shelves and there are some objects that

he can’t see they’re occluded from his

point of view with a kind of gray piece

of wood 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 director standing

behind the set of shells 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 directors 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 normal

healthy intelligent adults than you make

errors about 50% of the time on that

kind of trial they move the white truck

instead of the blue truck so we give

this kind of task to adolescents and

adults meals have a control condition

where there’s no director and instead we

give people a rule we tell them okay

we’re going to do exactly the same thing

but this time there’s no director

instead you’ve got to ignore objects for

the dark gray background you’ll see that

this is exactly the same condition only

in the no director condition they just

have to remember to apply this us

somewhat arbitrary rule whereas in the

direct

condition they have to remember to take

into account the directors perspective

in order to guide their ongoing behavior

okay so if I just show you the

percentage errors in a large

developmental study we did this is a

study ranging from age 7 to adulthood

and what you’re going to see as the

percentage errors in the adult group in

both conditions so the gray is the

director condition and you see that our

intelligent adults are making errors

about 50% 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

adolescents there was 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 there’s still a

significant improvement in the director

condition between mid adolescence and

adulthood and what this means is that

the ability to take into account someone

else’s perspective in order to guide

ongoing behavior which is something by

the way that we do in everyday life all

the time is still developing in mid to

late adolescence so if you have a

teenage son or daughter and you think

you sometimes think they have problems

taking other people’s perspectives

you’re right that they do and this is

why so we we sometimes laugh about

teenagers we’ve parodied sometimes even

demonized in the media so that canta

pikal teenage behavior they take risks

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

the very notion of their dad singing in

public was enough to make them behave so

people often ask well is adolescents the

kind of recent phenomenas is it

something we’ve invented recently in the

West and actually the answer is probably

not there are lots of descriptions of

adolescents in history that sound very

similar to the descriptions were used

today so there’s a famous quote by

Shakespeare from The Winter’s Tale where

he describes adolescents as follows I

would there were no age between ten and

three and twenty or that youth would

sleep out the rest but there’s nothing

in the between but getting wench’s with

child

wronging the ancient tree stealing

fighting he then goes on to say having

said that would any but these boiled

brains of nineteen and ten twenty hunt

in this weather

so almost 400 years ago Shakespeare was

portraying adolescents in a very similar

light to the light that we portray them

in today but today we try to understand

their behavior in terms of their

underlying changes that are going on in

their brain 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 the

important drive to become independent

from one’s parents and to impress one’s

friends in adolescents 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 deep

inside the brain and it’s involved in

things like emotion processing and

reward processing it gives you the

rewarding feeling out of doing fun

things including taking risks it gives

you the kick out of taking risks and

this region the regions within the

limbic system have been found to be

hypersensitive to the rewarding feeling

of risk-taking in adolescence compared

with adults and at the very same time

the prefrontal cortex which you can see

in blue in the slide here which stops us

taking excessive risks is still very

much in development 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 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 sometimes seen as the problem

with adolescents - 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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