Teenagers take dumb risks because of a flaw in their brain chemistry, suggests a new study

Risk taking, thrill seeking.
Risk taking, thrill seeking.
Image: Reuters/Andy Clark
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Whether you call it naïveté or bad judgment, teenagers are notorious for making ill-advised and sometimes dangerous choices—smoking, binge drinking, and reckless driving among them—for a thrill.

New research suggests at least some of these mistakes may be due to imbalanced neuron activity during adolescence.

In a study published Thursday (Sept. 29) in Current Biology, researchers from Dartmouth University manipulated the brains of adult rats to mimic rat brains going through puberty. They found that with “teenage” brain chemistry, rats took a lot longer to learn patterns of when they’d be rewarded, and when they wouldn’t. Researchers hope that these findings can be a first step towards developing ways of curbing risky behavior in teenagers.

Scientists have known that teenagers have a more active reward circuit than adults or children, especially when they’re in front of their peers. They’ve also observed that as the brain develops from childhood to adulthood, there’s a period of time when the prefrontal cortex, which mediates rational decision making, underperforms, while the nucleus accumbens, which plays a part in pleasure-seeking, ramps up in activity. Some of these changes occur as as teenagers develop skills in abstract thinking and advanced reasoning, and can also help spur exploration in new interests. In childhood and adulthood, these two regions experience more balanced activity. Scientists suspect these regions—and the imbalance—play a role in risk-taking adolescent behavior.

To test this hypothesis, the Dartmouth research team injected 10 rats with a chemical that allowed them to non-invasively alter the adult rat brains to behave like pubescent rat brains. Then they trained the altered rats and twelve control rats to respond to different patterns of external stimuli. A sound alone signaled that the rats would be given food, but a light coupled with the sound meant no food was coming. “Adolescent” rats took an average of 22 times to learn not to expect food when they only heard a tone. Rats with unaltered adult brains took an average of 13 trials to learn the same pattern. The results imply that it takes adolescent brains longer to learn when they’ll actually benefit from certain behavior.

Of course, a small study on rats doesn’t provide the same kind of evidence that a larger study on human subjects would yield. It’s difficult to scale up the findings to common human behavior, like driving fast, drinking, or using drugs. Additionally, the temporary alteration of brain activity could just be one of many reasons that teenagers feel more comfortable taking on risks.

Still, David Bucci, a neuroscientist and co-author of the paper, explained that rats can serve as a sound model for human brain activity. “Given the existence of the same brain regions and circuits in humans and rodents, and data showing that adolescents of both species show the same alterations in activity, it’s a pretty safe bet that our results are mimicking the state of the adolescent brain in either rats or humans,” he wrote in an email. He also speculated that this effect would be greater in male rats than females. (Boys tend to make riskier choices than girls.)  

“Our hope is that these findings will inform new means to minimize the potential for engaging in drug use and other harmful behaviors during this important period of development,” Bucci said in a statement.