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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