signals than they did in previous years, leading to a delayed bedtime. With puberty also comes new social pressures. Even though they need only a little less sleep than children, adolescents are expected (or want) to adopt adult-like wake and sleep times. Their schools convene earlier in the morning. At the end of the day, there is homework, after-school activities, and spending time with friends. Intellectually and socially, their world is exploding. Even after bedtime, communications such as text messaging provide a continuing source of stimulation—and sleeplessness. The net result is the need to catch up on lost sleep. In one study, researchers surveyed sleep habits in Swiss, German, and Austrian girls for up to nine years after their first menstrual period. The girls slept almost two hours longer per day on weekends than on weekdays, compared to less than an hour of catch-up in younger children and adults. Sleep debt has serious consequences, including reduced mental performance, depressed mood, impaired health, and weight gain. Fully reorganize the brain. Many of the brain changes we have described may be organized and shaped by hormone signaling. Although sex and stress hormones rise during late childhood and adolescence, in most cases researchers have found little evidence for a direct effect of hormones on typical adolescent behavior. Hormones are a key component for organizing the neural circuitry, but by itself testosterone is not very predictive of risk taking. The combination of a poor parent-child relationship with high testosterone has somewhat more predictive power. In adolescence, a good relationship forged in your child’s early years can pay off. This principle extends to siblings too: better relationships with brothers and sisters improve adjustment during adolescence. A degree of impulsivity and aggression is probably unavoidable in life, but in some cultures, adolescent urges play a positive role. For example, among immigrants in big-city Chinatowns, aggression by male adolescents toward potentially violent intruders can protect the community from harm. Among the Mbuti, a hunter-gatherer group in the Congo, adolescents act on behalf of the group to punish deviations in adult behavior with mockery and even vandalism. One hallmark of adolescent behavior in people and other mammals is an increase in what behavioral scientists call approach, the seeking of new social contacts and situations. Combined with other changes, this tendency can lead to the making of new friends—and also, sometimes, rebellion against older family members. Some conflict is typical, though extreme emotional turmoil in relaOne name for this adolescent tendency, social jetlag, suggests that they might be able to use some tricks of long-distance travelers. Here are a few: 1. Opening the blinds in the morning will activate the melanopsin pathway in your retinas. At this time of the circadian clock, exposure to light creates a tendency to get up a little earlier the next day. 2. Evening light leads to a later bedtime the next day. Combine that with a natural tendency to stay up, and it’s a recipe for continued night-owl behavior. So even if sleep isn’t coming easily, turn down the lights. And turn off that cell phone! 3. Exercise leads to secretion of melatonin by the pineal gland. An evening soccer game or run might be just the thing to start a brain on the road to sleep. Relationships with parents is experienced by only about one in ten adolescents. This happens in other species as well. For instance, adolescent rats sometimes attack their parents. Another typically teenage behavior, the tendency to seek novelty, is likely to be driven by the brain’s reward systems. Dopamine is a neurotransmitter involved in initiating action and movement and in signaling rewarding events. In brain scanning data, the orbitofrontal cortex and other regions that receive dopamine-secreting inputs are still maturing during the teen years. The serotonergicsystem—involved in sensation, movement, and mood—is also changing in the adolescent years. Awkwardness and moodiness might be linked to this change. Another change in the brains of adolescents is a proliferation of receptors for the signaling chemical oxytocin. (Oxytocin is a neuro peptide—that is, a peptide used as a neurotransmitter.) Neuroscientists found that oxytocin mediates a wide variety of bonding behaviors. In people, oxytocin is secreted during feelings of romantic and parental love. Both mothers and fathers of an infant or a small child have more oxytocin; the higher their oxytocin, the more they touch, play with, and otherwise socially engage with their child—and each other. Indeed, these signals sometimes get crossed, so that a new mother having a loving thought toward her partner might feel her milk drop. Romeo and Juliet would also have felt a newly strengthened oxytocin signal. Adolescence is a time when the interplay between brain and environment takes on new complexity. Early adolescent brain changes increase a child’s appetite for stimulation and social contact, while self-regulatory systems continue to mature through late adolescence. In modern society, adolescence is viewed in terms of the delay between sexual maturation and true independence. Indeed, sexual, physical, and intellectual maturation are spread out over a decade or more, providing many opportunities for growth and change. What an adolescent does with this biologically defined period of transition depends on his or her culture—and the choices that come along the way. Around the world, how and when people enter society during this process varies, ranging from child workers to continuing students with children of their own. In all cases the brain has found ways to adapt to local circumstances—a testament to its flexibility. Reprinted with permission
Missoula, Montana
June 23-26, 2011