Adolescence: freeing the frontal cortex from the straightjacket of genes

Robert Sapolsky observes that

adolescence is the time of life when someone is most likely to join a cult, kill, be killed, invent an art form, help overthrow a dictator, ethnically cleanse a village, care for the needy, transform physics, adopt a hideous fashion style, commit to God, and be convinced that all the forces of history have converged to make this moment the most consequential ever, fraught with peril and promise.

The teenage brain is unique. It’s not merely an adult brain that is half-cooked or a child’s brain left unrefrigerated for too long. Its distinctiveness arises from a key region, the frontal cortex, not being fully developed. This largely explains the turbulence of adolescence. It also reflects an important evolutionary pressure.

The frontal cortex is the most recently evolved part of the human brain. It’s where the sensible mature stuff happens: long-term planning, executive function, impulse control, and emotional regulation. It’s what makes you do the right thing when it’s the harder thing to do. But its neurons are not fully wired up until your mid-20s.

What about the effects of peer pressure?

Teenage vulnerability to peer pressure is worsened by the fact that such pressure rarely takes the form of hesitant adolescents coerced into joining in the fun of committing random acts of kindness. Instead, pressure disproportionately takes the form of “deviance training,” increasing the likelihood of risky sexual behavior, poor health habits, substance abuse, and violence. As has been said, the greatest crime-fighting tool available to society is a 30th birthday.

The pain in not belonging:

One brain-imaging study reveals the neural depths of adolescent pain in not belonging. Put someone in a scanner to play a video game with two other individuals, and manipulate things so that the subject believes they are being ostracized. In adults, this social exclusion activates the amygdala along with other limbic regions associated with pain, disgust, anger, and sadness. But then the frontal cortex kicks in—“Come on, it’s a stupid game”—and the limbic structures quiet down. Do the same with an adolescent and the frontal cortex remains silent and that agonized limbic network of teenage angst wails.

What about the tsunamis of hormones?

The slowpoke frontal cortex is not the only explanation for teen behavior. Another factor comes into play that keeps that teen brain off balance, namely gonadal hormones like estrogen and progesterone in females, and testosterone in males. This helps explain why adolescence is more turbulent than childhood—the frontal cortex is immature at both ages, but the tsunamis of hormones haven’t started in pre-adolescents. Hormones have numerous effects on the function of both the limbic system and frontal cortex. Testosterone decreases the ability of the frontal cortex to communicate with and rein in the amygdala. Not surprisingly, landmarks of adolescent maturation in brain and behavior are less related to chronological age than to time since puberty.

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.

Sure, adolescence has its down sides, but it has its abundant pluses—the inventiveness, the optimism, the empathy. Its biggest plus is that it allows the frontal cortex time to develop. There’s no other way we could navigate the ever-increasing complexity of our social world.

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