National Geographic : 2011 Oct
• connections, allowing us to generate and weigh far more variables and agendas than before. When this development proceeds normally, we get better at balancing impulse, desire, goals, self-interest, rules, ethics, and even altruism, gen- erating behavior that is more complex and, some- times at least, more sensible. But at times, and especially at rst, the brain does this work clum- sily. It's hard to get all those new cogs to mesh. Beatriz Luna, a University of Pittsburgh pro- fessor of psychiatry who uses neuroimaging to study the teen brain, used a simple test that il- lustrates this learning curve. Luna scanned the brains of children, teens, and twentysomethings while they performed an antisaccade task, a sort of eyes-only video game where you have to stop yourself from looking at a suddenly appearing light. You view a screen on which the red cross- hairs at the center occasionally disappear just as a light ickers elsewhere on the screen. Your in- structions are to not look at the light and instead to look in the opposite direction. A sensor detects any eye movement. It's a tough assignment, since ickering lights naturally draw our attention. To succeed, you must override both a normal im- pulse to attend to new information and curiosity about something forbidden. Brain geeks call this response inhibition. Ten-year-olds stink at it, failing about 45 percent of the time. Teens do much better. In fact, by age 15 they can score as well as adults if they're motivated, resisting temptation about 70 to 80 percent of the time. What Luna found most interesting, however, was not those scores. It was the brain scans she took while people took the test. Compared with adults, teens tended to make less use of brain regions that monitor performance, spot errors, plan, and stay focused---areas the adults seemed to bring online automatically. This let the adults use a variety of brain resources and better resist temptation, while the teens used those areas less o en and more readily gave in to the impulse to look at the ickering light---just as they're more likely to look away from the road to read a text message. If offered an extra reward, however, teens showed they could push those executive regions to work harder, improving their scores. And by age 20, their brains respond to this task much as the adults' do. Luna suspects the improvement comes as richer networks and faster connections make the executive region more e ective. These studies help explain why teens be- have with such vexing inconsistency: beguil- ing at breakfast, disgusting at dinner; masterful on Monday, sleepwalking on Saturday. Along with lacking experience generally, they're still learning to use their brain's new networks. Stress, fatigue, or chal- lenges can cause a mis re. Abi- gail Baird, a Vassar psychologist who studies teens, calls this neu- ral gawkiness---an equivalent to the physical awkwardness teens sometimes display while master- ing their growing bodies. e slow and uneven develop- mental arc revealed by these im- aging studies o ers an alluringly pithy explanation for why teens may do stupid things like drive at 113 miles an hour, aggrieve their ancientry, and get people (or get gotten) with child: They act that way because their brains aren't done! You can see it right there in the scans! This view, as titles from the explosion of scientific papers and popular articles about the "teen brain" put it, presents adolescents as "works in progress" whose "immature brains" lead some to question whether they are in a state "akin to mental retardation." Troublesome traits like idiocy and haste don't really characterize adolescence. They're just what we notice most because they annoy us or put our children in danger.