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

Prefrontal cortex is an interesting brain area.

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

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

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

It's been shown to promote pre frontal cortex development where a lot of cognition is happening.

Now what does a pre frontal cortex do for you that should justify the entire architectural overhaul of the human skull in the blink of evolutionary time?

Interestingly, this approach also emphasizes the significance of the prefrontal cortex for the generation of the visualization.

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.

We had this broad patch of area called the lateral prefrontal cortex that went way down in activity, and I'll summarize that for you here.

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

Well, it turns out the pre frontal cortex does lots of things, but one of the most important things it does is it is an experience simulator.

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.

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.

For one thing, those circuits almost always involved in human awareness include the lateral prefrontal cortex (due to the part it plays in short term memory and executive and control functions).

And one of the main reasons our brain got so big is because it got a new part, called the frontal lobe. And particularly, a part called the pre frontal cortex.

Tree Bark

The bark is also a paler gray color.

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.

The lush heart note, Melaleuca bark note which does not contain any Melaleuca bark, because it s totally forbidden.

The bark is thick and deeply fissured.

The cerebral cortex is made up of gray matter.

The outer bark and stem are astringent.

They give us that beautiful brown crust.

So you have the prefrontal cortex here, lighting up in red.

On mature trunks, the bark is gray and shaggy.

And so as the sensory input comes in and feeds from the old brain, it also goes up into the neocortex. And the neocortex is just memorizing.

The sugars in the dough caramelize in the crust.

The crown is rounded and the bark is smooth and grey.

The side and the underside of the prefrontal show deep vertical grooves.

So at least as far as these aspects of our awareness depending on the prefrontal cortex are concerned among them the knowledge who we are and the ability to plan and to make decisions there is reason to assume that humans are distinct even from other primates.

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're flying through the cortex of my colleague's brain.

General uses Food A sweetened drink is made from the bark.

Why do teenagers seem so much more impulsive, so much less self aware than grown ups? Cognitive neuroscientist Sarah Jayne Blakemore compares the prefrontal cortex in adolescents to that of adults, to show us how typically teenage behavior is caused by the growing and developing brain.

This big cortex, or whatever, we're pretty proud of ourselves.

And on top of it, we have this memory system called the neocortex.

On branches and young trunks, the bark is smooth and silvery gray.

And it's always drifting. The pack ice is always drifting.

And you know, of course, what'll happen if you do a pre frontal lobotomy.

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.

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.

They become accessible to the oven for caramelization to give us a beautiful crust.

Only the crust can caramelize. It's the only place that gets hot enough.

The bark is brown gray, very rough, with deep cracks in adult specimens.