Teenagers seek out risk-taking behaviors, the research suggests, because the brain systems involved in decision-making mature at different times.
The section of the brain most involved in emotion and social interaction becomes very active during puberty, while the section most critical for regulating behavior is still maturing into early adulthood.
This explains, Steinberg says, why teens are so susceptible to peer pressure and why education and prevention efforts designed to keep teens from engaging in risk-taking behaviors don't work all that well.
"We have tried to prevent these behaviors by educating kids about the dangers of things like smoking, drinking, taking drugs, and unprotected sex," he tells WebMD. "The thinking has been if they know about the dangers they won't do these things, but that is clearly not true."
Child and adolescent psychiatrist Jay Giedd, MD, performed much of the brain-imaging research highlighted in the analysis in his role as chief of brain imaging in the child psychiatry branch of the National Institute of Mental Health (NIMH).
Giedd tells WebMD that the way the brain develops creates a period of risk-taking vulnerability that is greatest around puberty.
"That is when the balance is tipped most in favor of high emotions and risk taking," he says. "The key parts of the brain involved in controlling impulses and risky behavior don't really reach maturity until about age 25."
He adds that risk taking among adolescents is seen in all mammals, suggesting a biologic basis for the behavior that helped the class survive.
"It is risky to leave your parents and go out on your own, but that same behavior is also good for the gene pool," he says.
In one of Steinberg's earlier studies, the number of risks teens took in a video driving game more than doubled in the presence of their peers, compared to when they engaged in the game alone. The presence of peers increased risk taking by 50% in college undergraduates who participated in the study, but it did not influence the number of risks older adults took.
When peers are not around and in situations which are not emotionally charged, teens tend to be much better at controlling impulsive or risky behaviors.
The findings have major implications for public health and prevention efforts targeting teens, Steinberg says.
While education is certainly important, he says programs aimed at persuading teens not to engage in dangerous behaviors appear to have little impact.
"I don't want to suggest that we should stop educating teens about these dangers, but we shouldn't kid ourselves. Just because we are giving kids the facts, that doesn't mean that we are changing their behavior," Steinberg says.
"Kids have much more difficulty controlling their impulses and regulating their behavior than adults do," he says. "We need to provide more structure to regulate it for them."
That means focusing more on ways to keep teens from getting into trouble, like raising the driving age or imposing restrictions on new drivers. Many states have already imposed such restrictions.
But parents have a bigger role to play than government, by monitoring the behavior of their teens and imposing their own rules to protect them from harm.
"We know from actuarial data that having other teenagers in the car when an adolescent is driving is an even bigger risk factor for an accident than alcohol," Steinberg says. "Yet a parent who wouldn't ever let their child get behind the wheel after drinking usually doesn't think twice about letting that child drive a car with four other teenagers, a blaring stereo, and a cell phone."