Beyond the 'average' adolescent

Some look back on their teenage years with a sense of pride, at their rebellious nature, others cringe at the thought. Although we have our own personal experience of passing through that stage, teens are so often misunderstood and regarded with considerable wariness. Shakespeare once wrote: 'I would there were no age between sixteen 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'. In opening the British Psychological Society's Annual Conference Sarah-Jayne Blakemore (University College London) sought to provide a more tolerant and evidence-based perspective on adolescent development, looking to the teenage brain to partially explain this age group's risky behaviour.

Professor Blakemore told the gathered audience how she became interested in teen brain development – through working with people with schizophrenia. Testing patients in a hospital outside Versailles during a post-doc, Blakemore realised that all of them reported onset of the condition at the end of adolescence. Why should this devastating and floral illness remain almost dormant during childhood and the teenage years? Unlike other developmental disorders such as autism and ADHD, 'schizophrenia waits, and shows itself at the end of adolescence'. But it's not alone in that: Blakemore showed that 75 per cent of adult mental disorder has the onset before the age of 24, and mostly during adolescence. Blakemore thought the answers might lie in the typical development of the teenage brain.

Although often adolescence is described as starting with puberty and ending when a person gains a stable independent role in society, there are massive cultural differences in when this may occur. In some cultures people marry and start having children very young, whereas in the West many people continue to live with their parents and study until their 20s or 30s. But Blakemore argues that adolescence is, in fact, a distinct biological period which presents itself across cultures and in every one of us. Typical adolescent behaviours, including heightened risk-taking, peer influence, impulsivity and self-consciousness, can be seen across cultures and even across species. Adolescent rats show increased risk-taking and increased exploration, during this period, and even drink more alcohol when in the company of other adolescent rats!

On a more sombre note, Blakemore pointed out that adolescent risk-taking has a real effect on teenage mortality rates, with accidents related to risky behaviours being the leading cause of death of people in that period of life. But why do adolescents generally take more risks? And in what circumstances? Blakemore outlined Larry Steinberg's research, which took three age groups, 13-16, 17-24 and 25 and over, and asked them to play a driving video game. Somewhat surprisingly the adolescents took around the same number of risks – jumping lights, speeding etc - as the adults and young adults. So in optimal circumstances, where the adolescents can concentrate on the task in hand, the stereotypical view is not borne out by the research. However, when the groups were watched doing the task by a couple of friends, the number of risks that adolescents took tripled and the number of risks the young adults took doubled. The adults were unaffected. 'The critical factor is peer influence,' Blakemore said.

This fits our real world picture of when teenagers start to take risks, such as smoking: it's when they're with others. And data from British car insurance companies show that adolescents have more accidents if they have a similar-aged passenger in the car, whereas in adults the pattern is reversed. What could it be about peer influence that has an effect on risk taking? Blakemore suggested that adolescents have a vested interest in being accepted by their peer group, 'probably for evolutionary reasons' – they need to become independent from their families.

In research with Catherine Sebastian, Blakemore showed the emotional side of this peer influence. Using a simple game-based paradigm of social exclusion, they found that adolescents reacted to apparent social exclusion with a significantly greater drop in mood than adults did. 'This perhaps explains how perfectly intelligent, rational adolescents make risky decisions… the social factor weighs in particularly heavily on the see-saw of decision making.' Imagine a 13-year-old girl whose friends all smoke, and they offer her a cigarette. Is it more risky to say yes to a cigarette, knowing the health risks of smoking, or to say no and risk being socially ostracised? 'These decisions are not so crazy if we think about them in the context of the importance of their peer group,' Blakemore concluded.

Referring to research she conducted at the Science Museum, Blakemore explained that adolescents don't judge situations or decisions as objectively less risky – they do not feel invincible – they are just particularly influenced by the risk perceptions of other teenagers and less so by adults. 'It always surprises me that health doesn't just focus on social norms and peer effects,' Blakemore mused. Find the most popular kid in a class and educate them about various risky behaviours, she said: research suggests that the perceptions of the whole class can then change towards the views of that cool child.

But what about the neuroscience behind this behaviour? Blakemore pointed out that, until recently, it was unclear at what point the brain stopped developing. fMRI and MRI data has taken us far closer to understanding, showing that brain development continues throughout adolescence and even into the 20s and 30s.  The pre-frontal cortex has a role in the assessment of risks and impulsivity and Jay Giedd's work has shown that the grey matter volume in this area peaks in late childhood and early adolescence, followed by a significant decline during adolescence. What does this correspond to? Blakemore discussed 'synaptic pruning', a 'moulding of the brain during adolescence that is heavily dependent on the environment, as one factor.

Turning to 'theory of mind', the ability to infer the mental states of others, Blakemore outlined MRI data showing that each of the four areas within the so-called 'social brain network' parallel the increase in grey matter volume in childhood and decrease during adolescence seen in the pre-frontal cortex. Yet nine developmental fMRI studies show that medial pre-frontal cortex activity in social cognition tasks is higher in adolescents than in adults. Blakemore feels this may reflect a different cognitive strategy for adolescents in this kind of perspective taking task. She also pointed to a potential mismatch between the maturity of the emotion-led limbic system and the under developed pre-frontal cortex to explain the greater propensity for adolescents to take risks.

Blakemore closed her talk with a startling example of how looking solely at average data can give us a false picture of brain development in adolescence – showing the huge differences among individuals in their brain development during this period. She concluded that individual differences should be the subject of further investigation, particularly looking into how genetics, culture, a person's environment and social group affect brain development. 'It's the individual differences that are going to be more meaningful and interesting than the averages.'

- Ella Rhodes is The Psychologist's journalist.

- See also an archive piece from Professor Blakemore on the social brain of the teenager, along with her Doctoral Award piece from 2002, and reports on her website on the lives of scientists and her work with a young theatre group.

Professor Blakemore will be appearing as part of 'The Psychologist and Wellcome Trust present at Latitude Festival', alongside author Fiona Neill in a session hosted by The Psychologist editor Dr Jon Sutton.

- More reports from the Society's Annual Conference will appear on this site over the coming days and weeks, with extras in the July print edition.