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1
THE SECOND DECADE: WHAT CAN WE DO ABOUT
THE ADOLESCENT BRAIN?
—
By Catherine Sebastian
—
With a recent UNICEF report showing our youth to be
the unhappiest in the industrialised world (UNICEF,
2007; BBC, 2007), the time has come to seriously review
the way in which our society treats its young people. It is
debatable whether our overarching motivation to do so is
an altruistic one (to improve lives), or one of self-
preservation (fear of A Clockwork Orange-style random
violence). Both are, at this point, equally compelling.
In the past decade, cognitive neuroscientists
have joined the attempts of psychologists, social workers,
youth workers and educators to understand behaviour
during the teenage years. Cognitive neuroscience is a
relatively young discipline which attempts to link
cognitive processes such as memory, attention and
decision-making, with activity in the brain (see
Gazzaniga, 1999 for an overview). Brain activity is
measured indirectly by looking at behaviour, or
increasingly using brain imaging and recording methods.
Even more recently, social cognitive neuroscience has
begun to look at the neural underpinnings of processes
such as emotion and interpersonal interaction. As a
result, it has been fascinating to discover a basis in the
brain for phenomena such as the role of emotion in
decision-making; phenomena which until now have been
the preserve of philosophy and literature.
This article will look at evidence of neural
differences between adolescents (between the ages of
around 10 and 16) and adults, and how this relates to
differences in behaviour. There may be a link between
changes in the brain during adolescence and
stereotypically 'adolescent' behaviour such as increased
risk-taking, poor self-control, and emotional instability.
But even if you could quantify all the causes of these
behaviours at a neural level, what implications would this
have? Could it lead to effective interventions at the
interpersonal or societal level? Perhaps the cognitive
neuroscience of adolescence is merely an academic
exercise. But before we can look at implications, I will
review the key findings from the neuroscience literature.
Structure of the Teenage Brain
The human brain is composed of around 100 billion
nerve cells or ‘neurons’. The cell bodies comprise the
'grey matter', and are heavily interconnected via fibres
known as ‘axons’. These fibres are coated in a fatty
substance called myelin which acts as an insulator,
enabling electrical signals to be transmitted more
efficiently. The insulated axons bundle together to
form 'white matter', much like a bundle of electrical
cables. While it was long assumed that the brain was
fairly unchanging after early childhood, it is now
known that both white and grey matter continue to
develop well into our twenties. Indeed, some areas of
the brain continue to manufacture new neurons to
replace old ones throughout the lifespan.
Particularly intriguing are the changes that
have been found to occur at the onset of puberty.
Although the relationship between pubertal hormone
release and brain development is not fully established,
it is known that a cascade of neural changes is
initiated early in adolescence. This drives the
transformation of the brain from that of a child to
that of an adult. This makes evolutionary sense – as
the body reaches sexual maturity, the drive to leave
home and find a mate must be matched by a brain
that is well-equipped to negotiate the risks and
challenges this poses.
Studies (e.g. Sowell, Thompson, Holmes,
Jernigan, and Toga, 1999; Paus et al., 1999) have
shown that the volume of white matter increases
steadily throughout adolescence, particularly in the
frontal and parietal cortices; regions of the brain
associated with complex abilities such as planning,
paying attention, and interacting with other people.
This means that the capacity of the brain to conduct
signals efficiently from one region to another
increases throughout adolescence. At the same time,
changes in grey matter are also occurring, although
these are more complex and vary between brain
regions. As a general rule, grey matter density varies in
an ‘inverted U shape’, i.e. volume initially increases
and then gradually decreases again. This is thought to
reflect changes in the number of connections or
‘synapses’ between neurons. At the onset of puberty
(around the age of 11 in girls and 12 in boys), there is
a proliferation of synapses. However, during the
following important years, redundant synapses are
pruned away (see Paus, 2005 for a review). This
results in more efficient, faster adult networks,
capable of more sophisticated information processing.
It is an important principle of the brain that more
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isn’t always better: it’s the quality, not quantity, of the
connections between brain cells that counts.
Functioning of the Teenage Brain
So what do these structural alterations to the adolescent
brain mean for behaviour? First, it’s important to note
that areas undergoing the most profound restructuring at
this time include some of our most sophisticated
hardware. Most of the brain is fully developed by early
childhood, and the behavioural differences between
adults and adolescents are actually subtle (although it
might not always seem that way!). For example, teenagers
have no trouble making the complex but automatic visual
calculations necessary to work out when an approaching
car will reach their location. However, a teenager may
decide that they have time to cross the road before it gets
there, whereas an adult might decide to play it safe and
wait. This is of course a generalisation, but it illustrates
that the most profound differences between adults and
adolescents occur at the decision-making, or executive,
levels of processing. Anatomically, the brain areas
subserving these functions are located in the prefrontal
cortex (PFC), situated at the very front of the brain. The
PFC is larger in humans, relative to body size, than in
most other animals, and is thought to control many of
our unique abilities. These include executive abilities such
as forward planning, self-control, reasoning, and
decision-making, as well as social cognitive abilities such
as mentalising (the ability to infer what someone thinks,
feels, or believes).
Experiments have revealed some quite surprising
differences between adults and adolescents on tasks
involving these areas. For example, the Iowa Gambling
Task is often used to assess the functioning of the
ventromedial PFC, a region at the very front of the PFC
just above the eye sockets. It is thought to be involved in
the evaluation of rewards for the purposes of making
decisions, and is often studied using gambling tasks that
provide an explicit measure of the decisions people make
in the face of specific risks and rewards. In the Iowa
Gambling Task, four decks of cards are laid out in front
of the participant: cards represent either a monetary
reward or loss, and participants must choose from the
decks with the aim of maximising the amount of money
they gain over time. Two of the decks contain cards
offering high rewards but also heavy losses, while the
other two offer more modest rewards but also smaller
losses. The decks are rigged so that the latter two decks
will yield the greatest gain over many trials. Normal
adults start by sampling all four decks, but gradually shift
their choices to the ‘good’ decks. People with damage
to the ventromedial PFC do not learn this, and
continue to take risks on the ‘bad’ decks.
Crone and van der Molen (2004) gave this
task to people aged from 6 to 25 years. They found
that although all but the youngest subjects showed
some shift towards the good decks over time, the 10-
15 year olds took a lot longer than the young adults to
make the shift. Even at the end of the experiment
they were only choosing the good decks 55-60% of
the time – well below adult levels, and similar to
patients with damage to the ventromedial PFC. It
could be that the immaturity of this brain region
underpins findings from studies of risk-taking
behaviour in the real world, which show that
adolescents are more likely than adults to engage in
risky activities such as unprotected sex, reckless
driving, and experimentation with drugs. If, as the
results suggest, young people are less good at
anticipating the outcome of events, perhaps they are
unable to accurately appraise the risk levels when
faced with a real-life choice.
But this is not the whole story. Other studies
have suggested that teenagers can accurately appraise
risk to the same degree as adults in a controlled
experimental situation, but when faced with a real-
world situation this does not necessarily translate into
a sensible decision. Interaction with the environment
is crucial here, and aberrant decision-making in
adolescence is often mediated by the presence of
peers. Gardner and Steinberg (2005) put teenagers
and adults in a driving simulation game. Half the
subjects played alone, and the other half played with
two friends watching and giving advice. Both
teenagers and adults took few risks when driving
alone (e.g. driving through a yellow light instead of
stopping). However, in the presence of peers, the
teenagers, but not the adults, took many more risks.
This seems to reflect what we intuitively know from
our own experience. But why should this be the case?
Is it a purely social effect, reflecting the growing
importance of respect from peers? Is it due to
hormones? Or could there be an interaction between
the development of brain areas involved in decision-
making and those involved in social cognition, e.g.
knowing what others are thinking about you, and
indeed awareness of your own thoughts and
intentions?
Social cognition in adolescence has been
neglected until recently, but our lab and others are
now investigating processes such as taking another’s
point of view, processing of complex emotions,
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emotional/neural reactivity to stressful social situations
such as ostracism, and knowledge about our own and
others’ intentions and thoughts. For example, a recent
study by Blakemore et al. (in press) used functional
magnetic resonance imaging (fMRI) to look at the brain
areas activated when adolescents and adults make
decisions about either intentional causality (what you would
choose to do in a given situation) or physical causality (the
consequences of a natural event such as heavy rain, that
does not involve a human component). They found that
when asked to think about intentions, a larger area of the
medial PFC was activated in adolescents compared with
adults. This is another brain region known to undergo
substantial pruning during adolescence, and is an area
implicated in thinking about the self and other people.
The high level of activation may reflect processing by
networks that are still relatively inefficient at this kind of
social cognition. In addition, adults activated a different
brain area, the right superior temporal sulcus, more than
adolescents during the intentional causality task. This
area is commonly activated in mentalising tasks and in
predicting other people’s behaviour. It may be that the
shift towards using this region reflects the increasing
maturity of the mentalising network, although it should
be noted that adults and adolescents were using very
similar networks, just with subtle differences.
Implications for behaviour are still fairly speculative, but
it is certainly interesting that adults and adolescents are
processing social and self-related information using
different neural strategies.
Neural control of automatic or impulsive
behaviour is another issue to consider when attempting
to explain adolescent behaviour. Several studies have
looked at the ability of adolescents to inhibit a habitual
response when the task requires it. For example, Tamm,
Menon, and Reiss (2002) used a ‘Go/No-Go’ task, in
which participants had to press a button whenever they
saw a letter (‘Go’ stimulus), unless the letter was an X
(‘No-Go’ stimulus). Although this is a simple task, it
illustrates a very important executive function – the
ability to control our behaviour in a flexible and task-
dependent manner. Adolescents did not differ from
adults in terms of performance on the task, but the brain
activation as measured with fMRI revealed that
adolescents activated more of the PFC, and activated it
to a greater degree, to achieve the same effect. This
suggests that it is more effortful for adolescents to
suppress their impulses and respond to even simple
demands on cognitive control. If we combine this finding
with the evidence above about risk taking and social
processing (and consider that there are almost certainly
interactions between these functions that we have not yet
studied), it can be seen that adolescents are often facing
adult decisions with a brain that is not fully equipped
to deal with them.
Implications
In some sense British society already deals effectively
with the differences between adults and adolescents.
For example, important civil liberties such as suffrage
are not granted until the age of 18, and potentially
risky activities such as driving, smoking, and drinking
alcohol are also subject to an age restriction. Implicit
in these restrictions is the idea that a certain level of
maturity and responsibility is required for appropriate
decisions to be taken on these issues, and that by
virtue of reaching post-adolescence, the required level
is generally attained.
So British society is clear on what it doesn’t
want adolescents to be doing, but does it have a
realistic outlook on how it does want them to be
spending their time? I would argue that many
adolescents spend several of their teenage years in
limbo, dumped at school with little to fulfil the four
basic emotional needs identified by social
psychologists: control over one’s life, a meaningful
existence, high self-esteem, and belonging. Friends
can certainly provide a sense of belonging and high
self-esteem, but many young people face bullying,
racism, and discrimination, not just from peers, but
also from adults who have become so alienated by
teenage antisocial behaviour that they apply a policy
of universal hostility.
I would also argue that the way our society is
structured largely denies the possibility for teenagers
to have a meaningful existence, nor are they able to
feel in control of their lives. Poverty, low
expectations, and poor educational experience deprive
many of aspirations for the future, especially in our
individualistic society in which success is measured by
career advancement and material wealth. Teenagers
are often also unable to carve a niche for themselves,
academically or otherwise, due to a restrictive
curriculum, a ‘one size fits all’ educational policy, and
underinvestment in affordable activities outside
school. It is interesting here to consider education and
youth services in other industrialised nations that
scored far higher on the happiness of young people
than the UK in the UNICEF report (UNICEF, 2007).
In other industrialised nations such as the
Netherlands and Sweden there is less emphasis on
exams, a wider range of options other than the classic
‘academic route’, and more emphasis on the
4
development of social skills before children reach
adolescence. Findings from neuroscience research on the
adolescent brain are not going to change society, but they
might be able to provide clues about how social and
educational policies interact with the developing brain
during adolescence, and thus support links between
policy and measures of adolescent experience.
More immediately, we might ask whether
neuroscientific findings can be used practically to
improve the experience of the average teenager. The
brain is a complex structure that develops in tandem with
the rest of the body, and in response to the external
environment. Therefore, except in the case of psychiatric
disorder, it would not be wise to intervene with
medication, even if it were to make the experience of
adolescence less turbulent. In some sense, adolescence is
meant to be a tough time. But parents, educators, and
teenagers themselves should be made aware of the role
that brain development will play in behaviour. Often, just
knowing the reasons for something can help us to feel
more in control, and it may promote understanding
between different age groups. If young people know why
they are more susceptible to peer pressure, or why they
feel like taking risks sometimes, or why they feel so
different from adults, this might at least go some way
towards helping them feel less alone and make them
better equipped to deal with decisions they have to face.
In addition to educating people in this way, it
may be possible to develop behavioural strategies to train
adolescents in ‘weak’ areas, by giving them progressively
harder computerised exercises in domains such as
cognitive control, or thinking about other minds, or
decision tasks requiring an individual to weigh and
compare different options in order to make a choice. Or,
particularly for social cognition, workshops and
discussion groups could be provided in which young
people discuss a situation from both their own and
another’s perspective in order to refine mentalising
abilities. These abilities could then be extended by
introducing schemes that give young people a sense of
social responsibility, e.g. mentoring for younger children,
or charity work in the community. Whether such tasks
would generalise to teenagers’ lives in the real-world is
debatable, as is the assumption that this sort of practice
would translate to more ‘adult’ activity at the neural level.
Perhaps time just has to take its course. There is also the
social argument that teenagers are meant to experiment
and make mistakes, and that it puts even more pressure
on them to ask them to behave like responsible adults.
Yet people are taking important decisions at a young age
(e.g. when to have sex, whether to use contraception,
whether to drink or take drugs, see UNICEF, 2007), and
something needs to be done to ensure that they are
equipped to make them. Although neuroscience
cannot address these issues alone, it may well be of
use in combination with the efforts of other fields
such as psychology, education, and social work.
Conclusions
There is clear evidence that the adolescent brain is
very different to that of an adult, and that substantial
restructuring of the prefrontal cortex needs to occur
during these important years. Cognitive and social
cognitive neuroscience are now starting to reveal how
differences in brain structure and function relate to
typically ‘adolescent’ behaviours such as risk taking,
susceptibility to peer pressure, poor perspective-
taking, emotional instability, and more effortful self-
control. But there is still a long way to go. What are
the interactions between these behaviours and the
environment? For example, do teenagers find it more
difficult to regulate and control the feelings they
experience during negative social experiences (e.g.
bullying and ostracism), and might this then make
them more likely to conform to peer pressure? Until
we know more about how the discoveries made in the
lab relate to the everyday experiences of adolescents,
it will be difficult to put our research to practical use.
Nevertheless, this emerging field provides a new angle
on an increasingly thorny problem: parents, educators
and policy makers should not just consign these
findings to academic oblivion, but should work with
scientists to find new applied solutions.
© Catherine Sebastian, 2007
PhD 1, Psychology (Perspectives on the Self from Adolescence
and Asperger Syndrome)
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