The Teenage Brain: Spock Vs. Captain Kirk : NPR Ed Adolescents get a bad rep for being irrational. The bad news: It's kinda deserved. The good news: Teen brains come equipped with an internal Mr. Spock, trying to keep them safe.

The Teenage Brain: Spock Vs. Captain Kirk

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The reckless image of adolescence looks something like this - a teenager, say about 16, behind the wheel, smoking, drinking and driving dangerously. But now it's believed that the changes in the brain that lead to the famously bad choices of adolescence actually start earlier, around 11 or 12, along with puberty. This week, member station WNYC in New York is running a series on the beginning of adolescence. It's called Being 12. And Cory Turner of the NPR Ed team contributed this story, set inside the wilds of the adolescent brain.

CORY TURNER, BYLINE: Let's start with an experiment. At Temple University, psychology professor Laurence Steinberg and his team put a bunch of adolescents into an FMRI machine - a brain scanner - and asked them to play a driving game.

LAURENCE STEINBERG: And you come to a series of intersections and the lights turn yellow, and you have to decide whether to put the brakes on or not.

TURNER: Now, what do you think the adolescents did in this situation? Wrong. They did not blow through the yellow every time.

STEINBERG: When adolescents are playing this game by themselves, they don't take any more chances than adults do when they're playing it by themselves.

TURNER: And that's a big deal, Steinberg says, because the adolescent brain gets a bad rep for being consistently impulsive. His latest book, called "Age Of Opportunity," is an attempt to set the record straight. Being 12 or 17 doesn't mean you're hardwired to always make bad choices. Why, then, do adolescents make so many bad choices? To find out, Steinberg added a twist to his experiment - he gave his subjects an adolescent crowd.

STEINBERG: This doubles the number of chances that adolescents take, but has no effect on the number of chances that adults take.

TURNER: In short, an adolescent's weakness is other adolescents.

B J CASEY: Adolescence is a time, really, when the brain is being marinated in gonadal hormones.

TURNER: B.J. Casey is a neuroscientist at Weill Cornell Medical College and she says much of the turmoil in the 12-year-old brain comes from changes in two places. First - the frontal cortex, one of the last areas of the brain to mature.

CASEY: It helps to link past experiences to the current situation and consider what the future consequences are of choices and actions that are made.

TURNER: The prefrontal cortex is our voice of reason. Steinberg calls it the brain's CEO. Casey likens it to this guy...

(SOUNDBITE OF TV SHOW, "STAR TREK")

LEONARD NIMOY: (As Mr. Spock) The odds against you and I both being killed are 2,228.7.

TURNER: That is, of course, Spock from "Star Trek."

CASEY: The rational person on the starship Enterprise. And he often has to keep the passionate Captain Kirk at bay.

(SOUNDBITE OF TV SHOW, "STAR TREK")

WILLIAM SHATNER: (As Captain Kirk) Traitors. I'll hang you up by your Vulcan ears. I'll have you all executed.

NIMOY: (As Mr. Spock) I think not. Your authority on this ship is extremely limited, Captain.

TURNER: In Casey's analogy, Captain Kirk is the limbic system.

(SOUNDBITE OF TV SHOW, "STAR TREK")

SHATNER: (As Captain Kirk) There's only one thing I want to say to you, Commodore - get my ship out of there.

TURNER: The limbic system is the emotional center of the brain, always on the lookout for threats and rewards. When it spots either, it sends a message to the prefrontal cortex. See, the limbic system can't make sense of these things on its own. Kirk needs Spock. And here's the problem - for kids in adolescence, the prefrontal cortex is still developing. And it just can't keep up with the limbic system, which goes into reward-seeking hyper-drive, especially with other kids around.

CASEY: It's as if these emotional regions hijack the prefrontal systems and it leads to a choice that they make that's a bad one, and that they even know is a bad one.

TURNER: The limbic system doesn't just flag rewards in things like alcohol and sex. A 12-year-old gets a kind of high simply by being around other adolescents. They're wired to seek each other out, developing the skills they'll need to leave their parents, feed and protect themselves and raise children. In the short term, that means cloudy judgment and potentially risky behavior. But adolescence is all about the long view. Cory Turner, NPR News, Washington.

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