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Moving Parts: A lecture on the adolescent brain

March 4, 2013
Teenage boys with a mobile phone

Teenage boys with a mobile phone

If there was one key message from Jay Giedd’s lecture at UCL, it was this: teenagers, and particularly their brains, deserve more credit. Simple, but with the constant barrage of bad press about young people it is easy to forget that adolescence is a unique and valuable part of human development.

Adolescence has played a vital role in human evolution.  All social mammals undergo a period of adolescence characterised by increased risk-taking, novelty seeking and a shift towards peer-based interactions. These behaviours encourage adolescents to move away from the family unit and live independently – an advantageous tactic adopted by many species in the course of their evolution.

What is unusual about human adolescence is its length. Whereas the Neanderthals were turfed out on their heels at the tender age of 11 or 12, homo sapien evolved with a much longer period of growth and development – a whole decade longer.  This extended period during which young brains are malleable, and can grow, allows more time for the brain to adapt to suit its environment – which is a great evolutionary advantage.

This remains as true today as it was at the end of the last ice age. Giedd spoke of the vast changes to our environment brought about by the digital revolution. Technology is continually being updated and is becoming increasingly complex, and teenagers are better placed than anyone to take advantage of these changes. They are, as Giedd observed, “young enough to embrace change, but old enough to grasp new technology”.

Until quite recently, relatively little was known about what went on in our brains during this crucial period in our development. But in the past 15 years a whole sub-section of neuroscience has emerged, devoted to understanding the development of the adolescent brain. Giedd’s lecture was jointly hosted by the UCL Institute of Cognitive Neuroscience, the UCL Centre for Adolescent Health and the UCL Centre for Developmental Cognitive Neuroscience (CDCN). The CDCN, which has over 500 members and representations from diverse faculties across the university, is at the forefront of research into the developing brain.

Giedd himself is a practicising Child and Adolescent Psychiatrist and Chief of Brain Imaging at the Child Psychiatry Branch of the National Institute of Mental Health in the USA. In recent years he has overseen the Branch’s Brain Development Study, which uses MRI scanning to monitor brain development in children, adolescents and young adults between the ages of 5 and 25. In addition to MRI scanning, participants undergo cognitive and behavioural tests, and are assessed for neuropsychological disorders. The team are literally, Giedd says “watching the brain grow”.

But the term “growth” may be misleading. By the age of 5 or 6, a child’s brain is already 90 per cent the size of an adult’s. During our teens, the brain grows “not by getting bigger, but by becoming more specialised and more connected.” Exactly how it develops is dependent on our environment and, to some extent, on the lifestyle that we chose. Giedd used the analogy of a tree: the systems in our brains which are most useful, and most used, are developed and strengthened – these are the branches which grow and flourish – but other systems which are used less frequently or are superfluous, are ‘pruned’.  Our teens really are our ‘formative years’. As Giedd put it, “[it is] empowering to think we have a lot of choice in what you spend your time doing and that what you choose changes how your brain develops”.

However, as we all know, there are less appealing sides to adolescence. Giedd describes it as a period of “opportunity and vulnerability” – a time at which we should be at “the top of our game” but we are all too often dogged by problems.  The proportion of accidental deaths is higher amongst teenagers than in other age groups, and neuropsychological conditions are often first diagnosed during adolescence.

His research looks at the “path, mechanisms and influences” of adolescent development in the hope that in the future a greater understanding of these processes might bring the possibility of interventions. For example, the difference in the rate of development of the frontal lobes compared to other parts of the brain. The pre-frontal cortex is well known to be associated with long-term planning and foresight. Scientists now believe that the pre-frontal cortex develops slower than other parts, perhaps not reaching full maturity until as late an age as 25. Could this lag perhaps account for the lack of restraint and inattention to consequences exhibited by many ‘problem’ teens?

Giedd traced a pattern, throughout history and across cultures, of examples of “the 25 cut-off” – when societies have identified the age of 25 as an important tipping point in a person’s development. In Ancient Rome, 25 was the minimum age for a gladiator; in the US a person must be 25 years old before they can serve as a Representative; in the UK it is the age at which you cease to qualify for a Young-Persons Railcard. It is an intriguing, if somewhat romantic, possibility that perhaps common sense has always told us what neuroscience is now substantiating: it takes us much longer to ‘grow up and out of it’ than we might suppose.

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