So you have the prefrontal cortex here,

Prefrontal cortex is an interesting brain area.

And you do that by measuring the relative activation of the left prefrontal cortex in the fMRl, versus the right prefrontal cortex.

The arrows indicate peak gray matter volume in prefrontal cortex.

One of the brain regions that changes most dramatically during adolescence is called prefrontal cortex.

So we had this focal area called the medial prefrontal cortex that went way up in activity.

We had this broad patch of area called the lateral prefrontal cortex that went way down in activity,

So this is a model of the human brain, and this is prefrontal cortex, right at the front.

like the dorsal lateral prefrontal cortex or the superior temporal gyrus, there is a profound loss of gray matter.

In very short, people who have more activity in the right side of the prefrontal cortex are more depressed, withdrawn.

And you see activity in some regions we've seen today, medial prefrontal cortex, dorsomedial, however, up here, ventromedial prefrontal cortex, anterior cingulate, an area that's involved in lots of types of conflict resolution, like if you're playing Simon Says, and also the right and left temporoparietal junction.

This is an area in the prefrontal cortex, a region where we can use cognition to try to overcome aversive emotional states.

It goes to the nucleus accumbens, all the way up to the prefrontal cortex, orbital frontal cortex, where decisions are made, high level.

One of the big surprises is how limited our attention is, and it comes back to how small and fragile the prefrontal cortex is.

In red is an area that's active in the prefrontal cortex, the frontal lobe of the brain, and in blue is this area that was deactivated.

So in my lab, we bring adolescents and adults into the lab to have a brain scan, we give them some kind of task that involves thinking about other people, their minds, their mental states, their emotions, and one of the findings that we've found several times now, as have other labs around the world, is part of the prefrontal cortex called medial prefrontal cortex, which is shown in blue on the slide, and it's right in the middle of prefrontal cortex in the midline of your head.

And when you're happy what we call positive valence you squirt dopamine into the prefrontal lobes, which makes you a breadth first problem solver you're more susceptible to interruption you do out of the box thinking.

But if I say, See a region of the brain, taking all the oxygen and glucose from all these other regions, and your prefrontal cortex suddenly has very little resources to do much, you can see that, right?

The reptilian part of our brain, which sits in the center of our brain, when it's threatened, it shuts down everything else, it shuts down the prefrontal cortex, the parts which learn, it shuts all of that down.

You prune away the weaker branches so that the remaining, important branches, can grow stronger, and this process, which effectively fine tunes brain tissue according to the species specific environment, is happening in prefrontal cortex and in other brain regions during the period of human adolescence.

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.

So what happens when we pay attention is that the prefrontal cortex, the sort of executive part of our brains, sends a signal that makes a little part of our brain much more flexible, more plastic, better at learning, and shuts down activity in all the rest of our brains.

This region is more active in adolescents when they make these social decisions and think about other people than it is in adults, and this is actually a meta analysis of nine different studies in this area from labs around the world, and they all show the same thing, that activity in this medial prefrontal cortex area decreases during the period of adolescence.

And this region, the regions within the limbic system, have been found to be hypersensitive to the rewarding feeling of risk taking in adolescents compared with adults, and at the very same time, the prefrontal cortex, which you can see in blue in the slide here, which stops us taking excessive risks, is still very much in development in adolescents.