Scientists: Teen Brain Still Maturing

Sheila Montgomery and her son Zack, 17, are shown, Tuesday, Nov. 20, 2007, at their home in Portland, Ore. (AP Photo/Rick Bowmer) (Rick Bowmer - AP)

_emotionally volatile.

_likely to take risks.

_reactive to stress.

_vulnerable to peer pressure.

_prone to focus on and overestimate short-term payoffs and underplay longer-term consequences of what they do.

_likely to overlook alternative courses of action.

Violence toward others also tends to peak in adolescent years, says psychiatrist Dr. Peter Ash of Emory University. It's mostly likely to start around age 16, and people who haven't committed a violent crime by age 19 only rarely start doing it later, he said.

The good news here, he said, is that a violent adolescent doesn't necessarily become a violent adult. Some two-thirds to three-quarters of violent youth grow out of it, he said. "They get more self-controlled."

Some of the changes found in behavioral studies are paralleled by changes in the brain itself as youths become adults.

In fact, in just the past few years, Steinberg said, brain scans have given biological backing to commonsense notions about teen behavior, like their impulsiveness and vulnerability to peer pressure.

It's one thing to say teens don't control their impulses as well as adults, but another to show that they can't, he said. As for peer pressure, the new brain research "gives credence to the idea that this isn't a choice that kids are making to give in to their friends, that biologically, they're more vulnerable to that," he said.

Consider the lobes at the front of the brain. The nerve circuitry here ties together inputs from other parts of the brain, said Dr. Jay Giedd of the National Institute of Mental Health.