Adolescent brain development

By Sarah-Jayne Blakemore, Royal Society Research Fellow and Professor of Cognitive Neuroscience at UCL. 

1. Adolescent brain development: What have we learned in the past 15 years?

Until about 15 years ago it was assumed that the vast majority of brain development takes place in the first few years of life. Up until that point, scientists did not have the technology to look inside the living, developing human brain. In the past decade, mainly due to advances in brain imaging technologies, in particular magnetic resonance imaging (MRI), neuroscientists have started to scan the living human brain at all ages, in order to track development changes in the brain’s structure – its organisation, including how much grey matter it contains – and also how it functions, across the lifespan. Many groups around the world are working in this area, and we now have a rich and detailed picture of how the living human brain develops. This picture has significantly changed the way we think about human brain development, by revealing that development does not stop in childhood, but continues throughout adolescence and well into adulthood.

Adolescence is defined as the period of life that starts with the biological changes of puberty and ends at the point at which an individual attains a stable, independent role in society. There are clearly large cultural differences in the age range associated with adolescence, and yet there are reports of adolescent-typical behaviour, such as heightened risk-taking and peer influence, in many very different cultures. There are also similarities in descriptions of adolescents throughout history. For example, in The Winter’s Tale Shakespeare portrayed adolescents as follows:

I would there were no age between 16 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.

Thus, almost 400 years ago, Shakespeare painted a similar picture of adolescents as we do now, and we are trying to understand this kind of adolescent-typical behaviour in terms of the underlying changes in the brain that characterise this period of life. One of the brain regions that undergoes the most striking and prolonged changes during adolescence is the prefrontal cortex. This is the part of the brain at the very front, and is involved in a wide variety of high level cognitive functions, including decision-making and planning, inhibiting inappropriate behaviour, stopping you taking risks, social interaction and self-awareness.

One of the main findings is that grey matter, which contains brain cell bodies and connections between cells in the prefrontal cortex, increases in volume during childhood, peaks in early adolescence and then starts to decrease in adolescence, and this decline continues throughout the twenties. So, the prefrontal cortex loses grey matter during adolescence. It has been proposed that this decline in grey matter volume partly reflects an important neurodevelopmental process: the loss of connections between brain cells (synapses) during development. This process, which is known as synaptic pruning, partly depends on the environment in that connections that are used are strengthened; connections that aren’t used are lost – they are pruned away. Synaptic pruning fine tunes brain tissue according partly to the environment. You can think of it as a bit like pruning a rose bush. You prune the weaker branches in order for the remaining branches to grow stronger. This is happening throughout adolescence in several cortical regions, including the prefrontal cortex.

A second line of inquiry involves scanning the brain using functional MRI (fMRI) to track changes in brain activity with age. Many fMRI studies have shown that brain activity associated with tasks such as decision-making, planning, inhibiting a response and reasoning, changes across adolescence.  For example, in my research group, we are particularly interested in the social brain – that is the network of brain regions that is used to understand other people. We bring adolescents into the lab to have a brain scan, and while they are being scanned we give them tasks that involve thinking about other people’s emotions, thoughts and feelings. Studies from our lab and from other labs shows consistently higher levels of activity in a social brain region called the medial prefrontal cortex in adolescents when they carry out social tasks that require understanding irony, thinking about social emotions such as guilt or embarrassment, or thinking about someone else’s intentions, for example. The different levels of activity within regions of the social brain might be because adolescents and adults use a different cognitive strategy (mental approach) to make social decisions. This is a hypothesis currently under investigation.

In order to look at cognitive approaches to social cognition, we carry out behavioural studies with adolescents, and we and other labs are finding that the ability to understand other people, for example to take another person’s perspective to guide decisions, is still developing in adolescence. At the same time, many studies have shown that the ability to plan and delay gratification is still developing during this period of life. Another area of adolescent research is risk-taking. It is well documented that teenagers tend to take risks, especially when they are with their peers. There appears to be a drive towards seeking the approval of peers, and becoming independent from one’s parents, in adolescence. Even adolescent rats and mice take more risks immediately after puberty than before puberty or in adulthood. One proposal that attempts to explain why risk-taking peaks in adolescence is to do with the brain’s limbic system – this is the brain system that gives us a rewarding feeling when we taking a risk. There is some evidence that in adolescence the limbic system is particularly sensitive to this rewarding feeling. And at the same time, the prefrontal cortex – which stops us taking risks and acting on impulse – is still developing.

2. Implications for education

Scientific evidence is showing that the brain systems involved in decision-making, planning, social understanding and risk-taking are developing in adolescence. This research might have implications for education, rehabilitation and intervention.

Adolescence represents a period of brain development during which environmental experiences, including teaching, can and do profoundly shape the developing brain. If early childhood is seen as a major opportunity, or a sensitive period, for teaching, so too might adolescence. It is only recently that teenagers have been routinely educated in the West and in many countries a large proportion of teenagers still have no access to education. UNICEF estimates that 40% of the world’s teenagers today do not have access to secondary school education. And yet the adolescent brain is malleable and adaptable. This is an excellent opportunity for learning and creativity.

A prevailing view in adolescent research is that certain behaviours, such as long-term planning, are desirable, while others, such as risk-taking, are undesirable. In certain situations, risk-taking is useful: taking a risk can give individuals a chance to obtain the preferred outcome. Indeed, risk taking in an educational context, for example asking a question in class or providing an answer that goes beyond the information in the textbooks, is a vital skill that enables progress and creativity. Although some adolescents use risk taking to achieve great things, many are worried about taking risks in the context of learning. The heightened risk-taking in this age group observed in certain contexts (e.g. smoking, drinking, unprotected sex, reckless driving) perhaps could be harnessed for learning and creativity. A shift from treating adolescent behaviours, especially risk-taking, in isolation to a model that integrates social environmental cues might enhance our understanding of adolescent behaviours and improve interventions. What is sometimes seen as the problem with adolescents’ risk-taking – poor impulse control, self-consciousness, and so forth – is actually reflective of brain changes that provide an excellent opportunity for education and social development.

Adolescence is a time of opportunity for learning new skills and forging an adult identity. The research on brain development in adolescence might have implications for “when to teach what” and could inform both curriculum design and  teaching practice with the aim of ensuring that classroom activities exploit periods of neural plasticity that facilitate maximal learning.

3. How far is your area of neuroscience from informing actual applications in schools?

This is a relatively new field although educators are generally very interested in adolescent brain development. Until 15 years ago, adolescent-typical behaviour was largely put down to changes in hormones and social environment, e.g. changing schools from primary to secondary school. We now understand adolescent-typical behaviour in terms of changes in the brain (as well as changes in hormones and social environments). Teachers and parents might find this helpful in understanding their students or children. However, it is too early to draw out specific implications for education that must be applied in the classroom.

Because certain brain regions are still developing in adolescence, it could be argued that the cognitive skills that rely on these regions should not be assumed to be fully mature in secondary school. For example, the ability to plan develops throughout adolescence, both in terms of performance on behavioural tasks and in terms of brain activity. This suggests that it might not be appropriate to expect a 13-year-old, for example, to be able to plan their homework, projects, schoolwork and so on, in the same way that a typical adult would be able to plan. Perhaps metacognitive lessons throughout secondary school would be useful to facilitate skills that are still developing in the brain for example, planning, inhibition and social cognition. Although of course randomised controlled trials (RCTs) would be critical in evaluating the outcome of any kind of intervention.

4. What are the limiting factors of applying this area of neuroscience to education?

Understanding how education can be tailored to the developing brain has got to be a good thing. However, this is a young field and there are still many questions to be answered. Adolescence might represent a period of increased neuroplasticity – these days we often hear people referring to adolescence as a ‘second sensitive period of brain development’. However, there is actually very little empirical research that has investigated this question. We do not yet know whether, for example, learning certain types of information is particularly efficient in certain periods during adolescence, or whether the brain is particularly efficient at adapting to changes in the environment during this period of life.

There is not much data on how the environment influences brain development in human adolescence. For example, how culture, playing video games, spending time on Facebook, multi-tasking between texting, Facebook and homework, and so on, affect brain development is not well understood. There might be negative effects on the brain of spending a lot of time on the internet every day. Alternatively, perhaps today’s teenagers will be techno-savvy, super-efficient multi-taskers.

There is some evidence of gender differences in the trajectories of brain development in adolescence, with cortical grey matter in boys developing more slowly in early adolescence than in girls. This mirrors the delay in puberty in boys relative to girls (on average). However, how or whether this should influence education is not well understood because there are significant individual differences in development and much overlap between the sexes.

We are just starting to learn more about how genetics influences brain development, and how brain development goes awry in individuals with developmental disorders and psychiatric conditions.

There are many potential opportunities for neuroscience to benefit the education of adolescents, indeed we have barely scratched the surface in hypothesising these potential opportunities, let alone testing them. Any applications must be systematically researched before classroom practice should change – with the input of both education professionals and neuroscientists – but it may be that in the future, secondary school education and social environments are tailored to the developing teenage brain.