What’s going on in the Teenage Brain?

23 January 2013

Interview with

Professor Sarah Jayne Blakemore, University College London

Hannah - Now, Harry Enfield's infamous sketch on Kevin's 13th birthday provides a comic take on what it is to become a teenager.  

The clock strikes midnight and Kevin loses the power of rational thought and speech and he becomes the parody of a moody stroppy teenager, embarrassed by everything that his parents do, and finding everything just 'so unfair'.

This entertaining extreme take on adolescence is being scrutinised by the scientists.  We speak with Professor Sarah-Jayne Blakemore who studies teenage brain at University College London.

Sarah -   It's only really recently that we've known that the adolescent brain changes so much.  Up until about 15 years ago, scientists just didn't really have a clue about what was going on in the adolescent brain.  

And so, these stereotypical adolescent behaviours, (although note, not all teenagers behave like Kevin, but some do) were mostly put down to kind of hormonal changes or social changes.  

But research in the last 10 or 15 years, mostly using magnetic resonance imaging (or MRI) scanning has enabled scientists to look inside the living developing brain at all ages and to track changes in both the structure of the brain, so its organisation, and also, how it functions, across their lifespan.  So, there is now actually a vast amount of research on the adolescent brain.  This research has just completely taken off in the last decade, but if I just focus in on a couple of key findings:

One of the brain regions that undergo the most protracted development in humans and during the adolescent period is called prefrontal cortex.  So that's part of the brain right at the front of your head and prefrontal cortex is disproportionately bigger in humans than in any other species.  And actually, it's involved in a whole load of higher cognitive functions that are much more sophisticated in humans than in any other species.  So things like decision making, planning what you're doing this evening or next week or even next year.  

The prefrontal cortex is also involved in inhibiting inappropriate behaviour, so stopping ourselves, taking risks for example.  It's also involved in understanding other people, so social cognition, and also, self-awareness.  

Now, we know from many different magnetic resonance imaging (MRI) studies on thousands and thousands of children and adolescents that the prefrontal cortex undergoes really quite profound changes during adolescence. 

So we know for example that in terms of structure, grey matter volume - so grey matter contains brain cell bodies and connections between brain cells called synapses and we know that in a human brain, in a human prefrontal cortex, grey matter increases during childhood.  Peak grey matter volume occurs in early adolescence - a couple of years later in boys compared with girls, so around age 11 in girls and 13 and boys probably because girls go through puberty a couple of year earlier than boys, and then decreases during adolescence.  So in other words, there's quite a large loss of grey matter in the prefrontal cortex during human adolescence, and that might sound bad, but actually, it's a really important process. 

We think it partly reflects the loss of excess connections which is a process known as synaptic pruning.  And synaptic pruning is a really important process, so it's partly dependent on the environment and that connections or synapses that are being used are strengthened, and synapses that are not being used in that particular environment are eliminated.  They're pruned away.

Hannah -   So, the necessary pruning or removable of surplus connections in the prefrontal cortex during adolescence might explain some of the behavioural changes associated with the teenage years.  There's also a second line of inquiry, measuring how the activity of the brain changes whilst teenagers are doing different tasks, and having their brain scanned using functional magnetic resonance imaging.  There's a huge amount of research coming out now in this area.  Sarah explains some of her recent results. 

Sarah -   In my lab, we're particularly interested in the social brain, that is the network of brain regions that are used to understand other people.  So for example, to understand other people's minds, their emotions, their mental states, their intentions, that kind of thing.  And what we tend to find is that during adolescence, there's a change in which the social brain functions. 

So, it's not that adolescents and adults are using completely different regions of their brain to understand other people.  They're not.  In fact, they're using more or less the same network of regions, but there's a change in the level of relative activity in the different regions of the network.  And one of these findings that we've replicated several times and other people, what the labs around the world have also found is that there's a decrease in the level of activity in a part of the social brain called the medial prefrontal cortex. 

So in other words, adolescents use the mid or prefrontal cortex more than adults do to do exactly the same kind of social cognition tasks involves thinking about other people's minds or emotions or intentions.  And we think this might be because adolescents and adults use a different sort of mental approach, a different cognitive strategy to make social decisions, and that's a question that we're now particularly interested in looking at.

Hannah -   And Sarah's lab has been doing some neat experiments and found that some social brain areas undergo maturation in association with how many years the people have been alive whereas other areas mature more in association with how far along in puberty they are.

Sarah -   This is the best study of its kind and now, we're trying to figure out why, what causes the differences in these two regions.

Hannah -   That was Professor Sarah-Jayne Blakemore from University College London, speaking about a new area of neuroscience of how the brain changes during the teenage years.  These findings could help to inform educational policy.  


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