A dolescence, that extraordinary developmental phase, is defined as the period between the onset of puberty and the achievement of a stable, independent role in society. While socio-cultural factors play an important part, behavioural changes have been a noted feature of adolescence throughout history and are even documented in the works of Aristotle. More recently, scientists have begun to research and understand the changes that occur within the human brain during this period and how they may influence behaviour.
Until about 20 years ago, it was assumed that the vast majority of brain development took place during the first few years of a child's life. This idea informed much of pedagogy and classroom practice.
But with the advent of new imaging technologies, such as magnetic resonance imaging (MRI), research methods are now available that allow scientists to look inside our bodies. Neuroscientists have started to examine the living human brain at all ages in order to track developmental changes in its structure and function. This has revolutionised our understanding of the brain. Many research groups around the world now work in this field and their combined efforts have revealed that brain development does not stop in childhood but continues throughout adolescence and even into adulthood. These changes in our understanding of the teenage brain are hugely important for how we think about education and how teachers approach their roles.
So, what have we learned? Images generated by MRI have revealed the highly organised architecture of the brain, from the outer surface (called the cortex) to other, deeper structures. The output of an MRI scan can be classified into white matter and grey matter, both of which undergo significant changes during adolescence.
White matter gradually increases in volume throughout childhood and adolescence before stabilising in adulthood. The increase in white matter is thought to reflect developmental changes that make communication between cells faster and more efficient.
Meanwhile, the developmental changes in grey matter volume vary according to region. One brain region that shows particularly striking and prolonged changes during adolescence is the prefrontal cortex, which is located at the front of the brain. This area is hugely important for educationalists.
What lies beneath
The prefrontal cortex is responsible for a wide variety of complex behaviours, including decision-making and planning, inhibiting inappropriate or risky behaviour, interpreting how other people think and feel, and self-awareness. Indeed, a number of studies have shown that the volume of grey matter in the prefrontal cortex is highest during childhood, then decreases during the adolescent years and stabilises in adulthood. The precise age at which these changes level off is dependent on the brain area, as well as factors specific to each individual, including their environment and genetics.
What, then, do these discoveries tell us about children's development? And how does this impact on teachers? Evidence suggests the existence of some early sensitive periods during brain maturation, in which an individual's environment profoundly shapes their development. For example, it is well documented that infants are especially adept at learning languages. And after the first year of life, sensitivity to speech not present in their native environment decreases sharply.
Less is known, however, about the existence of later sensitive periods. It is possible that areas of the brain undergoing prolonged periods of development may be particularly malleable to certain types of learning experience during adolescence. This is a key area for future research, which may contribute to the debate about which subjects should be taught at which time.
To investigate whether changes to the brain's structure relate to changes in behaviour, researchers have been devising ways to study the complex abilities that are thought to develop throughout adolescence. Our research group at the University College London Institute of Cognitive Neuroscience has targeted cognitive processes that are reliant on areas of the brain showing the most prolonged development, such as the prefrontal cortex.
This region forms part of the brain's social network, a system that is involved in understanding other people in terms of their behaviour, thoughts and emotions. This process is sometimes called mentalising, and plays a critical role in everyday social interactions and conversations (as well as teaching, of course). It is how we come to realise that another person may have different ideas, beliefs and opinions to our own.
Our research uses experimental tasks to study complex aspects of social cognition that are still developing during adolescence - for example, the ability to take into account the visual perspective of another person. In one task, participants of different ages had to choose objects to move from a set of shelves by following the instructions of a character who had a different viewpoint to them. We tested a large group of children and teenagers in schools and the laboratory, and found that performance improved with age until early adulthood. This suggests that the ability to take into account the perspective of others when communicating continues to develop throughout the teenage years and into early adulthood.
Adolescents also show differences in how their mood is affected by social information. A computer game called Cyberball simulates social exclusion and can be used to study the effects of social rejection at different ages. In this game, participants play catch with two other players who they believe are real peers connecting over the internet. In fact, the other players are fictional and are programmed to include or exclude the participant from the game. Using this task, our research group demonstrated that adolescents - particularly younger adolescents - showed a greater decline in mood after experiencing simulated social exclusion than adults did.
The reward of risks
As well as experiencing social anxiety, teenagers are stereotypically known for their risky behaviour. Scientists have used driving simulations to look at the number of risks - such as accelerating through a changing traffic light - taken by participants of different ages. When adolescents and adults performed the driving task alone, they took similar numbers of risks. However, when a couple of friends were standing behind them, teenagers took three times as many risks whereas adults continued to take the same number. Although these results were reached using a lab-based simulation, similar evidence can be found in data from car insurance companies. Young people have more accidents than adults and the majority occur when there are passengers of a similar age in the car.
Looking at how social factors influence adolescent behaviour and cognition can help to increase our understanding of why young people engage in risky behaviour. We all behave differently when we are in company, but other people's opinions appear to have particular influence on young people's decisions. For example, to an adolescent deciding whether or not to engage in smoking or binge drinking, is the bigger risk the fact that there are long-term health implications or that saying no could result in derision from their peers? Viewed in this context, it is likely that risky actions may be chosen because they have immediate positive outcomes that outweigh potentially adverse long-term consequences.
Consideration of how such choices are made is crucial to understanding teenagers' social decisions. Could it be that regarding adolescent behaviours as exploratory and potentially socially beneficial, as opposed to risky and negative, could enable the design of more effective education and health interventions? If adolescents are especially sensitive to social factors, might they be able to positively influence each other's learning and decisions through peer education and mentoring?
Within educational contexts such as school, work experience or university, risk-taking can be a vital skill that enables learning and creativity. Some apparent risks - for example, asking a question in class, providing an answer that goes beyond the information in the textbook or volunteering to give a presentation - lead to positive outcomes. Although some teenagers use risk-taking to achieve great things, many are worried about taking a chance in the context of learning.
Likewise, exploratory behaviours are essential in overcoming challenges such as leaving home or looking for a new job. Adolescents' heightened exploratory tendencies and sensitivity to social cues should be harnessed to foster learning and exploration of new topics and ideas. As we discover more about the development of the brain in the teenage years, scientists and teachers may be able to use this knowledge to develop classroom activities that exploit naturally occurring developmental changes.
Adolescence represents a period of development during which environmental experiences, including teaching, can and do shape the brain profoundly. If early childhood is seen as a sensitive period for learning, perhaps adolescence should be, too. It is only relatively recently that teenagers have been routinely educated in the West and in many countries a large proportion still are not. Children's charity Unicef estimates that 40 per cent of the world's teenagers do not have access to secondary education.
This is a tragic lost opportunity. The adolescent brain is malleable and adaptable, providing an excellent opportunity for learning and creativity.
Additional contributions by Delia Fuhrmann, Emily Garrett, Anne-Lise Goddings, Elina Jacobs, Emma Kilford, Lisa Knoll, Lara Menzies, Kate Mills, Ashok Sakhardande and Laura Wolf