The frontal cortex, freeing you from the straightjacket of genes

Robert Sapolsky – possibly the best neurobiologist science writer – has an article on teenagers and the krazy stuff they do:

Around the onset of adolescence, the frontal cortex is the only brain region that has not reached adult levels of grey matter, made up of neuronal cell bodies. It would seem logical that gray matter levels would increase thereafter. But no, over the course of adolescence, frontal cortical gray matter volume decreases.

These traits are exacerbated when adolescents are around peers. In one study, Laurence Steinberg of Temple University discovered that adolescents and adults, when left on their own, don’t differ in the risks they take in a driving simulator. Add peers egging them on and rates don’t budge in adults but become significantly higher in teens. When the study is carried out in a brain scanner, the presence of peers (egging on by intercom) lessens frontal cortical activity and enhances activity in the limbic dopamine system in adolescents, but not in adults….As has been said, the greatest crime-fighting tool available to society is a 30th birthday.

So what is the adaptive advantage of human brain development evolving this way? Potentially, there is no advantage…No, I think that the genetic program of brain development has evolved to help free the frontal cortex from the straightjacket of genes. If the frontal cortex is the last part of the brain to fully mature, it is by definition the brain region least shaped by that genome and most sculpted by experience. With each passing day, the frontal cortex is more the creation of what life has thrown at you, and thus who you become.

Frontal cortex, responsible for high cognitive functions and decisions, is like a ruthless lumberjack. The forest of neurons grows and, at the time of puberty, the lumberjack marches in and starts trimming anything that doesn’t seem useful. As Sapolsky suggests, what happens in adolescence is indelibly marked on your life. This suggests a curious possibility: does the age at which you go through puberty affect your future behavior? Children are going through puberty at a younger and younger age these days; and those who go through early or  late puberty will have vastly different experiences and cultural environments surrounding them. Since the age at which you go through puberty has some impact on your behavior – what are the differences in what you are learning during that time?

I couldn’t find any good references but if anyone knows anything, please let me know!

Update: I forgot to mention how this is a great example of genes putting you in a place where you have the opportunity to develop some phenotype. As in: perhaps early puberty does not cause children to be more wild than average, say, but it may more often put a child in an environment that makes the behavior more attractive.

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