The Cortical Factor: Developing the Optimum Brain

Take the teen-age brain - please!

First, a quick review: In our previous post, Robert Sapolsky of Stanford (pictured here) explained how the frontal cortex is about doing the harder thing, if it is the right thing to do. Essentially, the more developed cortical areas modulate our more primitive limbic impulses, including learned (and virtually automatic) behaviors that are no longer stored in the frontal cortex.

This tends to involve the frontal cortex, boosted by dopamine, amping up weaker neural circuits and inhibiting stronger ones. Those with cortical damage or dementia experience major system failures. Their brains default to the stronger circuits, even if these represent the wrong thing to do in the particular situation. They fail to stay on task. They give into temptation. They fail to delay gratification in pursuit of the long-term reward.

REM sleep offers a spectacular example of the frontal cortex going off-line. We dream all kinds of crazy stuff. We do things in our dreams we would never contemplate doing awake, that is assuming we are adults. But there is a strange phenomenon called teen-agers.

The frontal cortex is the last part of the brain to fully develop - to fully form all the myelin on its axons, to get its full complement of synapses. The front part of the brain fully goes online for the first time at around age 25. Younger than that and we’re dealing with limbic systems with feet.

Interestingly enough, says Dr Sapolsky, because the frontal cortex is the last part of the brain to develop it is the part of the brain least constrained by genes and most sculpted by environment and experience.

So - take an adult and take a teen-ager. Assign each one a task and give a greater reward than anticipated. Dopamine levels go up, driving frontal metabolism, but a lot higher in the teen-ager. Then change things around. Do not give out the reward. Dopamine levels go down, only much lower in the teen-ager. Says Sapolsky:

The gyrations are much more extreme. The dopamine-driven metabolic changes in the frontal cortex are more dramatically large for reward, are more dramatically having the floor fall out from under it for lack of reward, for disappointment. It is a system that is essentially less regulated.

Major bummer: The frontal cortex loses neurons as it ages, which explains your grandmother telling you that your new hairdo looks rotten.

Can elevated resting metabolism in the frontal cortex be too much of a good thing? Dr Sapolsky gives the example of repressive personalities, individuals who are highly regimented, highly disciplined, not depressed or anxious, who do not express emotions very readily and are very bad at reading emotions in other people. “This is the roommate who always has all the work done three weeks before the due date.”

But low resting metabolism in the frontal cortex is not such a good thing, either. Think sociopath. Give a sociopath a routine brain task and they have to activate more of the frontal cortex than other people do.

Meanwhile, see how long a marshmallow on the table lasts with a four-year-old kid in the vicinity. Can the kid rein in his impulse with the promise there will be more marshmallows in 20 minutes if he leaves that one alone? In other words, how many frontal synapses do you have? Funny you should ask. The kids who held out the longest scored much higher on their SATs and other success measures years later.

Depressing fact: Already by age five there is a relationship between your socio-economic status and the thickness of your frontal cortex and its resting metabolic rate. What is that all about? This is the part of the brain that has one of the highest rates of receptors for glucocorticoids. Glucocorticoids are released in response to stress, and when too many of them are on the rampage neurons atrophy. Get born into the wrong family, be raised with the stress of poverty and already by age five the size and activity of the brain has taken a major hit.

Says Sapolsky: “That is one of those factoids that should have people rioting at the barricades.”

Instead, we have the phenomenon of Presidential candidate Mitt Romney, who recently declared: “I'm not concerned about the very poor.”

Have no fear, there is a neurobiological explanation for that. There is also an explanation for your moral outrage. More to come ...

Highly recommended: Dr Sapolsky's 25-part video lecture series, Human Behavioral Biology.