Teenager’s changing brains
Dr. Guilherme Neves
Professor Sarah-Jayne Blakemore from the UCL Institute of Cognitive Neuroscience recently gave a talk as part of the NEUReka! seminar series at the Centre for Developmental Neurobiology, King’s College London. She shed light on the changes happening in teenager’s brains and how they modify their relationship with society. Importantly, she discussed how the latest evidence-based studies could point the way to improvements in public health approaches to this challenging and poorly understood critical developmental stage.
Throughout history, teenagers have always posed a challenge to society. It is a favourite sport in adult circles to mock and despair at the changes in behaviour stereotypically observed in adolescents: impulsiveness, risk-taking and increased reliance on peer group influence as opposed to adult authority figures. It turns out this has been happening since the times of Socrates and Aristotle at least, and the changes in adolescent behaviour can be tracked throughout history, cultures and even through evolution. A fascinating study shows us that even adolescent mice and rats increase their ethanol consumption when in the presence of peers1,2. Prof. Blakemore powerfully argued that it is pointless to fight the rising tide: adolescence is a critical developmental period essential for children to achieve adult independence and integration within a social network. We should do our best to understand it, so we can help our adolescents most effectively.
Prof. Blakemore is a very accomplished communicator, having participated in many media projects, a successful TED Talk with over 2.7 million views, and recently publishing a book. Her book, 'Inventing Ourselves: The Secret Life of the Teenage Brain', won the Royal Society Science Book Prize 2018. She captivated an audience largely unfamiliar with her main field of specialisation: human cognitive neuroscience. She started with an acknowledgement of the important gap remaining between the findings she was about to present from the areas of human behaviour and changes observable in large anatomical areas, and the findings being made in molecular and cellular neuroscience institutes around the world at the molecular and cellular level. In her view, the challenge can be partially met with better technology, but also with increasing exposure to each other’s findings, such as during these seminars.
Adolescence is defined as the period between sexual maturity at puberty and adult independence. One of the most controversial questions in the field is whether the concept of adolescence is conserved across different cultures, with some authors completely dismissing adolescence as a concept recently invented by affluent western societies. Carefully answering the questions surrounding adolescence requires very expensive, long and complex studies. For example, adolescents from 11 different countries showed higher levels of sensation-seeking and risk-taking, and lower levels of self-regulation5, compared to younger and older participants. For Prof. Blakemore, an important characteristic of adolescent behaviour that has great explanatory power is the increasing influence of the peer group in shaping behaviour choices, particularly regarding risk-taking.
To understand the argument, it is useful to consider the concept of social exclusion risk. This is the risk that you will be excluded from your chosen social group. This can have very damaging results at a time of development where the social networks are being built, and are still very fragile and unstable. In fact, adolescents are hypersensitive to social risks3, and they take social risks into account when considering the health and legal risks of drinking, smoking or driving at speed. An interesting study from Prof. Blakemore’s group showed that young adolescents’ assessment of risk is influenced more strongly by the risk perception of other teenagers, compared with the risk estimates given by adults4. These ideas have been further backed by successful public health interventions where the impact of peer influence on adolescent behaviour was factored in the strategy, such as in bullying campaigns at school and anti-smoking campaigns.
Finally, we turned to the hardest questions to address with currently available technology: what changes are happening in adolescent brains that could explain some of these behavioural results? Three general mechanisms have been explored that would lead to increased sensitivity to peer influence: 1) increased reward for peer acceptance, 2) increased arousal induced by the presence of peers and 3) increased capacity for mentalising – the recognition of mental states and emotions in other people. There were no clear cut messages during this last section, as it is an area of active research. It is clear that adolescent brains are changing at a very fast rate, increasing in white matter and decreasing in grey matter, while the overall volume remains constant. Possible explanations that have been advanced are increased myelination, increased axon size and increased synaptic pruning, but these hypotheses are hard to test. A great puzzle clearly laid out by Prof. Blakemore was the enormous variability in individual developmental brain growth profiles.
The importance of studying the development of the human brain during adolescence cannot be overemphasised. It has been estimated that over 75% of mental illnesses have an age of onset during adolescence. Findings from this area promise to help understand risk factors for mental illness, as well as inform public health interventions and educational strategies.
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