Other experiments shed light on why even book-smart teenagers come up short on judgment: Their brain parts aren't talking to each other. When Monique Ernst, a child psychiatrist and neurophysiologist at NIMH, uses functional MRI to watch teenage and adult brains engaged in playing a gambling game, she finds that the "reward" center lights up more in teens than in adults when players are winning, and the "avoidance" region is less activated in teens when they're losing. There's also less activity in teens' prefrontal cortex, which adults use to mediate the "yes!" and "no" impulses from other brain regions. "The hypothesis is that there is this triumvirate of brain regions that needs to be in balance" in order to produce wise judgments, says Ernst, whether that's to wear a seat belt or use contraception.
Does an unfinished brain make for bad behavior? There is as yet no proven link between bright blobs on an MRI and real-life behavior, but researchers are hard at work trying to make that connection. In a 2005 study by Laurence Steinberg, a developmental psychologist at Temple University, teenagers in a simulated driving test were twice as likely to drive dangerously if they had two friends with them—and brain scans showed that the reward centers lit up more if teens were told that friends were watching. A savvy parent might conclude that what's needed in the teen years is more guidance, not less.
In fact, study after study has shown that one of the most powerful factors in preventing teenage pregnancy, crime, drug and alcohol abuse, and other seriously bad outcomes is remarkably simple: time with responsible adults. "It doesn't have to be parents, necessarily," says Valerie Reyna, a professor of psychology at Cornell University. But it does mean that teenagers should be directly monitored by responsible adults so they have less time to get in trouble. Reyna thinks adults also need to teach what she calls "gist" thinking, or the ability to quickly grasp the bottom line. Instead, she says, teenagers often overthink but miss the mark. When Reyna asks adults if they'd play Russian roulette for $1 million, they almost universally say no. Half of teenagers say yes. "They'll tell you with a straight face that there's a whole lot of money, and they're probably not going to die. It's very logical on one level, but on another level, it's completely insane."
If it's any comfort, the evidence suggests that teenagers' loopy behavior and combativeness is hard-wired to push them out of the nest. Adolescent primates, rodents, and birds also hang out with their peers and fight with their parents, notes B. J. Casey, a teen brain researcher who directs the Sackler Institute at Weill Medical College of Cornell University in New York City. "You need to take risks to leave your family and village and find a mate."
A turbocharged learning machine. The revved-up adolescent brain is also built to learn, the new research shows—and those teen experiences are crucial. Neurons, like muscles, operate on a "use it or lose it" basis; a teenager who studies piano three hours a day will end up with different brain wiring than someone who spends that same time shooting hoops or playing video games. A 16-year-old who learns to treat his girlfriend with care and compassion may well develop different emotional brain triggers than one who's thinking just about the sex.
Only in early childhood, it turns out, are people as receptive to new information as they are in adolescence. The human brain is designed to pay attention to things that are new and different, a process called salience. Add in the fact that emotion and passion also heighten attention and tamp down fear, and teenagerhood turns out to be the perfect time to master new challenges. "You are the owners of a very special stage of your brain development," Frances Jensen, a neurologist at Children's Hospital Boston, tells teenagers in her "Teen Brain 101" lectures at local high schools. "You can do things now that will set you up later in life with an enhanced skill set. Don't waste this opportunity." (She was motivated to create the talks by her own befuddling experiences as a single mother of two teenage boys.)