The mysterious workings of the adolescent brain

3,833,341 views | Sarah-Jayne Blakemore • TEDGlobal 2012

Sarah-Jayne Blakemore
Cognitive neuroscientist

Sarah-Jayne Blakemore is Professor of Psychology at the University of Cambridge, UK, and leader of the Developmental Cognitive Neuroscience Group.

Joseph Geni, Translator
Morton Bast, Reviewer

00:00
Fifteen years ago, it was widely assumed that the vast majority of brain development takes place in the first few years of life. Back then, 15 years ago, we didn't have the ability to look inside the living human brain and track development across the lifespan. In the past decade or so, mainly due to advances in brain imaging technology such as magnetic resonance imaging, or MRI, neuroscientists have started to look inside the living human brain of all ages, and to track changes in brain structure and brain function, so we use structural MRI if you'd like to take a snapshot, a photograph, at really high resolution of the inside of the living human brain, and we can ask questions like, how much gray matter does the brain contain, and how does that change with age? And we also use functional MRI, called fMRI, to take a video, a movie, of brain activity when participants are taking part in some kind of task like thinking or feeling or perceiving something.

01:00
So many labs around the world are involved in this kind of research, and we now have a really rich and detailed picture of how the living human brain develops, and this picture has radically changed the way we think about human brain development by revealing that it's not all over in early childhood, and instead, the brain continues to develop right throughout adolescence and into the '20s and '30s.

01:24

So adolescence is defined as the period of life that starts with the biological, hormonal, physical changes of puberty and ends at the age at which an individual attains a stable, independent role in society. (Laughter) It can go on a long time. (Laughter) One of the brain regions that changes most dramatically during adolescence is called prefrontal cortex. So this is a model of the human brain, and this is prefrontal cortex, right at the front. Prefrontal cortex is an interesting brain area. It's proportionally much bigger in humans than in any other species, and it's involved in a whole range of high level cognitive functions, things like decision-making, planning, planning what you're going to do tomorrow or next week or next year, inhibiting inappropriate behavior, so stopping yourself saying something really rude or doing something really stupid. It's also involved in social interaction, understanding other people, and self-awareness.

02:23
So MRI studies looking at the development of this region have shown that it really undergoes dramatic development during the period of adolescence. So if you look at gray matter volume, for example, gray matter volume across age from age four to 22 years increases during childhood, which is what you can see on this graph. It peaks in early adolescence. The arrows indicate peak gray matter volume in prefrontal cortex. You can see that that peak happens a couple of years later in boys relative to girls, and that's probably because boys go through puberty a couple of years later than girls on average, and then during adolescence, there's a significant decline in gray matter volume in prefrontal cortex. Now that might sound bad, but actually this is a really important developmental process, because gray matter contains cell bodies and connections between cells, the synapses, and this decline in gray matter volume during prefrontal cortex is thought to correspond to synaptic pruning, the elimination of unwanted synapses. This is a really important process. It's partly dependent on the environment that the animal or the human is in,