As I’ve noted before, teenage brains may be almost fully grown, but they aren’t done maturing:
The first full series of scans of the developing adolescent brain — a National Institutes of Health (NIH) project that studied over a hundred young people as they grew up during the 1990s — showed that our brains undergo a massive reorganization between our 12th and 25th years. The brain doesn’t actually grow very much during this period. It has already reached 90 percent of its full size by the time a person is six, and a thickening skull accounts for most head growth afterward. But as we move through adolescence, the brain undergoes extensive remodeling, resembling a network and wiring upgrade.
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Beatriz Luna, a University of Pittsburgh professor of psychiatry who uses neuroimaging to study the teen brain, used a simple test that illustrates 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 crosshairs at the center occasionally disappear just as a light flickers elsewhere on the screen. Your instructions 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 flickering lights naturally draw our attention. To succeed, you must override both a normal impulse 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 often and more readily gave in to the impulse to look at the flickering 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 effective.
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Teens take more risks not because they don’t understand the dangers but because they weigh risk versus reward differently: In situations where risk can get them something they want, they value the reward more heavily than adults do.
A video game Steinberg uses draws this out nicely. In the game, you try to drive across town in as little time as possible. Along the way you encounter several traffic lights. As in real life, the traffic lights sometimes turn from green to yellow as you approach them, forcing a quick go-or-stop decision. You save time — and score more points — if you drive through before the light turns red. But if you try to drive through the red and don’t beat it, you lose even more time than you would have if you had stopped for it. Thus the game rewards you for taking a certain amount of risk but punishes you for taking too much.
When teens drive the course alone, in what Steinberg calls the emotionally “cool” situation of an empty room, they take risks at about the same rates that adults do. Add stakes that the teen cares about, however, and the situation changes. In this case Steinberg added friends: When he brought a teen’s friends into the room to watch, the teen would take twice as many risks, trying to gun it through lights he’d stopped for before. The adults, meanwhile, drove no differently with a friend watching.
To Steinberg, this shows clearly that risk-taking rises not from puny thinking but from a higher regard for reward.
“They didn’t take more chances because they suddenly downgraded the risk,” says Steinberg. “They did so because they gave more weight to the payoff.”
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We enter a world made by our parents. But we will live most of our lives, and prosper (or not) in a world run and remade by our peers. Knowing, understanding, and building relationships with them bears critically on success. Socially savvy rats or monkeys, for instance, generally get the best nesting areas or territories, the most food and water, more allies, and more sex with better and fitter mates. And no species is more intricately and deeply social than humans are.
Another non-discovery by brain imaging — which is incredibly crude compared with other investigative methods.
Everybody ought to know that IQ continues rising into the late teens (later in men than women) and therefore the brain continues to develop.