By Gene Beresin and Mireya Nadal-Vicens | September 16, 2013 | PBS’s Brains On Trial “Science Blog”
Teenagers are convinced they are ready to take the reins – to decide and act fully, no longer wanting to be held back by overly cautious adults who don’t really ‘get it.’ Neurobiologically speaking, the adolescent brain is poised for impulsivity and thrill-seeking.
In the documentary, “Brains on Trial with Alan Alda,” Jimmy Moran is on trial for attempted murder. Newly 18 years old, from a bad home, addicted to cocaine, questions of whether poor brain function affected his behavior the night he shot an innocent bystander remain constant. And being an adolescent, his brain was already primed for risky behavior.
Two separate but interconnected processes underlie teenage bravado. Firstly, the last wave of neurodevelopment, myelination, has yet to be completed. Myelination is the process of strengthening useful connections between neurons and omitting what is no longer needed.
By adolescence, most of the brain has been myelinated except for the frontal lobe, the center of “executive functioning” where planning, sequencing of activities and prioritizing long-range goals take place. Biologically, the long-range planning part of the brain is simply slower, less ‘hard-wired’ than the here-and-now information-processing parts of the brain.
Secondly, in part due to the slower inputs from the frontal lobe, thrills and rewards are just more thrilling and rewarding to teenagers. The reward center serves to motivate us by producing a small but powerful response to food, sex, and novel situations. Teenagers just get a whooping dose of this. In part due to the slower inputs from the frontal lobe, adolescents perceive short-term rewards as more rewarding than adults, and even small rewards are experienced as larger, better, more engrossing than they do to adults. Jokes are funnier, experiences are often, repeatedly ‘the best,’ everything is more urgent and more intense. Everything is worth doing because it feels so good, so right. The brakes, or the ability to contextualize certain pleasures and to appraise the relevant risks, are simply not hard-wired yet.
Three outside factors emphasize teenage impulsivity…