Teenagers are a famously reckless species. They floor the gas and experiment with drugs and play with guns; according to Centers for Disease Control and Prevention figures, more than 16,000 young people die each year from unintentional injuries. The most common-sense explanation for teens’ carelessness is that their brains just aren’t developed enough to know better. But new research suggests that in the case of some teens, the culprit is just the opposite: the brain matures not too slowly but, perhaps, too quickly.
In a paper just published in PLoS ONE — a journal of the Public
Library of Science — a team led by psychiatrist Gregory Berns of Emory University in Atlanta shows that adolescents who engage in more dangerous activities have white-matter pathways that appear more mature than those of risk-averse youths. White matter is essentially the brain’s wiring — the neural strands that connect the various gray-matter regions, where the actual nerve cells reside, that are otherwise independent of one another. Maturation of white matter is important because it increases the brain’s processing speed; nerve impulses travel faster in mature white matter.
Berns and his colleagues recruited 91 kids ages 12 to 18 and asked them to fill out a questionnaire about their tendency to engage in behaviors such as driving without a license, having unprotected sex and using drugs. Then they had the kids undergo a relatively new kind of brain scan called diffusion tensor imaging, a type of magnetic resonance imaging that is used to look at dense tissues like white matter. After analyzing the scans, the authors found a strong correlation between how risky the students described their behavior to be and how sophisticated their white matter was. The more mature the look of the brain, the more risk-taking the teenager tended to report.
The results challenge the accepted notion that teens make dumb decisions because their brains are immature. Although previous research has shown that most teens’ gray-matter structures — including those involved in decision-making — are less advanced than those of adults, as you would expect, until now no one had studied teens’ white matter, which works along with gray matter to produce decisions. The key part of white matter is called myelin, a fatty substance that coats the individual neural strands, or axons, that make up white matter. Myelination of axons begins during childhood and is completed at the end of adolescence, around the mid-20s. Myelination in the frontal lobe — the brain region responsible for decision-making — happens last, and it was in this region that the brains of risk-seeking teens in the study showed greater development compared with the frontal lobes of their more restrained peers.
