According to the World Health Organisation, suicide is the second leading cause of deaths in 15-29 year olds. Furthermore, the median age of onset for a range of mental health problems occurs during adolescence.
As the cornerstone of our future, we must provide adolescents with a solid framework of support, within which they can explore, grow and flourish. In order to do so, there is a pressing need to better understand the relationship between adolescent brain development and mental health risk.
Adolescence, the period of life between childhood and adulthood, is defined by the transition from parental dependence to relative autonomy. During this time, important changes take place in the structure and workings of the brain, and in the mental abilities which underlie some of the most sophisticated human behaviours.
One of the central events of adolescence is puberty. We now know that puberty impacts not just the production of gametes, but is also associated with changes in the brain and in behaviour. Of course, adolescence is also a socio-cultural phenomenon. Across time and place, its duration varies, as do its “typical” behaviours. Yet, studies conducted with humans and with non-human animals suggest there may be some biological commonalities of adolescence reflecting adaptive changes in brain and behaviour.
By all accounts, adolescence happens for a reason.
In humans, adolescence is often characterised as a risk factor in itself, something to be managed or controlled. However, current scientific thinking highlights carefully orchestrated, exquisitely sensitive neurodevelopmental change. We need to better understand this period of life if we are to address effectively the very real risks of adolescence, such as vulnerability to mental illness.
Developments in the brain
In many regions of the brain, the number of connections increases sharply in the first few months and years of life, and then gradually decreases to adult levels during puberty and adolescence.
Myelin, the fatty substance that insulates the brain’s axonal conduction fibres and speeds their electrical impulses, increases with age throughout childhood and adolescence. These changes in synapse density and myelin are thought to correspond to changes across age in the amount of grey and white matter observed using magnetic resonance imaging.
Across different regions of the brain, changes in grey and white matter take place at different rates. Parts of the brain involved in basic sensory processing tend to mature early in life - prior to adolescence. Brain regions involved in higher-level mental abilities, such as language, decision-making, and high-level social understanding, continue to mature during adolescence. There is evidence that these changes relate to maturation of mental abilities.
Early development of certain brain regions responsive to reward (e.g. subcortical regions) compared with later maturation of brain regions involved in thoughtful, effortful control of behaviour (e.g. prefrontal cortex) is thought to underlie enhanced adolescent reward seeking, exploration and risk-taking. These same mechanisms may also result in adolescence being a period of enhanced flexibility in learning and adapting to new environments.
Abuse and neglect during childhood and adolescence are associated with alterations in brain structure, but it’s worth noting that the neural impact of adversity may differ depending on its age of occurrence. In one study, childhood abuse was associated with alterations in subcortical and white matter structures, whereas abuse during adolescence was associated with abnormalities in prefrontal cortex.
A number of studies report gender differences in the adolescent brain. Understanding these differences may help us to understand the gender imbalance in depression and anxiety, which first arises during adolescence.
The age of puberty onset is dependent on both foetal and childhood nutritional intake. Population-wide changes in nutritional status may therefore impact brain development via mechanisms related to pubertal timing. We do not yet understand the implications of early or late pubertal timing on adolescent brain development, behaviour and mental health risk. Potentially, poor nutrition in utero and during childhood could have mental health consequences many years later.
Giving young people a better platform
As we learn more about the relationship between adolescent brain development and mental health risk, there may be implications for optimising adolescent development and wellbeing worldwide.
Adolescence is a critical period in human development – we must provide our young people with all the support they need to ensure a smooth transition to adulthood.
Dr Stephanie Burnett Heyes
Lecturer and British Academy Postdoctoral Research Fellow, School of Psychology
This Birmingham Perspective is an abridged version of a commentary published for UNICEF by Dr Burnett Heyes and Chii Fen Hiu, from the Department of Experimental Psychology at the University of Oxford.