The Teenage Brain

What is the fallout from a world that runs against the adolescent clock? There are four non-rem stages of sleep, and stages three and four, the deepest, which occur during the first third to first half of the night, are particularly useful to adolescents, who still have those frontal lobes to myelinate and lots of overall growing left to do (growth hormone is released during deep sleep). But because teenagers are so often deprived of rem sleep, which occurs during the last part of the night, their memories can suffer; they lose out on the stage of sleep that sees the information they’ve absorbed throughout the day replayed and consolidated. “Kids should be getting over nine hours of sleep,” says Smith. “Most are getting one to two hours less than they should. They’re missing quite a chunk of rem sleep and that’s important for understanding new things. If you don’t get much rem sleep, you’re not going to learn as fast as people who do.”

In one study, Smith set his subjects, who ranged in age from eighteen to twenty-two, to learning a logic task and then deprived them of the last half of the night of sleep. A week later, after the participants had recovered, the researchers tested them again. All had forgotten between 20 and 30 percent of what they’d learned. Once in a while, this kind of sleep loss is no problem. People can catch up. But when sleep deprivation becomes chronic, the consequences are compounded. “You’re forgetting 20 percent, but 20 percent every day,” says Smith. “And that goes on for months and months and months. That’s an inefficient system.”

Chronic sleep deprivation also increases the risk of developing depression (though, paradoxically, if someone is already depressed, sleep deprivation tends to help them feel better). This is a particularly serious issue for adolescents, as certain mental-health disorders tend to manifest themselves during these years. “There’s so much confusion over this,” Smith admits, “but one of the worries is if you just keep on with the sleep deprivation, eventually [that person] will become depressed. And we’re seeing a lot more depressed kids around now.”

But it’s not easy to fight nature; perhaps the best parents can do is to encourage a slowdown of activity at a reasonable time in the evening, keep technology out of the bedroom and caffeine out of the fridge, and let their kids catch up on weekends.

Most adults know what they’re up against because they remember their own night-owl days. They may have dabbled in rule-breaking, underage drinking, and general wildness as teenagers and now they shudder at the thought of their own children doing the same or worse. They were lucky, but will their kids inherit their luck? (The bad news for former hellraisers: some research suggests a person’s tendency to take risks is partly genetic.)

In fact, there’s some indication that cultivating unhealthy habits through this whole tumultuous period of development can have serious long-term effects. Those who start smoking during adolescence, for example, will likely have a much harder time quitting later in life than those who take up smoking in their twenties; the addiction, according to researchers at Duke University in Durham, North Carolina, appears to get hard-wired during the teen years.

Evidence from some studies also suggests that alcohol is more likely to damage memory and learning ability in the hippocampus of the evolving adolescent brain. At the same time, adolescent rats — whose brains are relatively similar to those of adolescent humans — suffer less from some of alcohol’s other effects, including sedation. That sounds like a good thing, but if it is indeed true for adolescents (and for obvious ethical reasons researchers don’t put adolescents through alcohol- related trials), it means they can drink more, and for longer periods — and therefore run a greater risk of long-term damage. Repeated alcohol use during these years may also lead to lasting memory and learning impairment — not to mention the fact that young binge drinkers are more likely to set themselves up with a lifetime alcohol- abuse problem.

This is one area where brain-research findings have affected how Giedd, the father of four, behaves as a parent. “In terms of substance abuse and alcohol, I’m a lot less hip now,” he says. “I wouldn’t have the mentality of, ‘Oh it’s better to have them do it at home.’ [Adolescence is] a very vulnerable time in brain development to be exposed to these other substances.” Giedd is surprised by how many parents say that their kids are going to drink and take drugs anyway, so they might as well do it at home, in a safe environment. “Biologically, it’s a time when the cement is setting. If people cannot do these things until the age of nineteen, the odds of them not having trouble as adults go up enormously.”

But experimenting, taking risks, and searching for good times are, it would seem, all part of the adolescent picture. As difficult as it is for parents to grasp, adolescents don’t always make poor choices just to get their goats, or because they’re suddenly gripped by temporary insanity. This sort of behaviour appears to be a predictable part of the identity-formation process, which begins in the early years but dramatically accelerates during adolescence. That’s when children begin playing different roles, trying on different hats, figuring out if they’re gay, straight, or bisexual, whether they’re a geek, a jock, or cool. At the same time, their frontal lobes aren’t fully developed, which means that the appetite for experimentation doesn’t necessarily go along with the capacity to make sound judgments or to see into the not-so-distant future. In other words, by their very nature, teenagers are not especially focused on, or equipped to assess, the consequences of their actions.

A 2004 mri study suggested that adolescent brains are less active than those of adults in regions that motivate reward-based behaviour. James Bjork, a neuroscientist at the National Institute on Alcohol Abuse and Alcoholism, and his colleagues conducted a brain scan on twelve adolescents between the ages of twelve and seventeen and a dozen adults aged twenty-two to twenty- eight. During the scan, the participants responded to targets on a screen by pressing a button; the object was to win (or avoid losing) varying amounts of money. The researchers found that areas of the brain associated with seeking gain lit up in both age groups. But in the adolescents, there was less activity. Adults, says Bjork, may have developed circuitry that enables them to motivate themselves to earn relatively modest rewards — the satisfaction felt after volunteering at church, say, or walking through a ravine. Adolescents, on the other hand, “may need activities that either have a very high thrill payoff or reduced effort requirement or a combination of the two.” Examples, he adds, would be “sitting on the couch playing violent video games or sitting on the couch and pounding alcohol.”