Unlocking The Teenage Brain
Adolescence is a wild ride for everybody—parents, teachers, and kids. There are fast-moving rapid and dramatic changes in biology, cognition, emotion, and interpersonal relationships. Just about everything that could change, does change. A good metaphor for puberty and the teen years is "starting the engine of a race car with an unskilled driver." The teen brain itself is different, and the teen skill set is different from what the same individuals had as preteens. This has been the recent focus of so many neuroscientific investigators that I can't begin to share all the latest discoveries with you here. We'll focus on just a few of the critical ones.
Many areas of the brain are under major construction during adolescence. In fact, the changes are as dramatic as those happening in an infant's brain. It's safe to call the teen years a "sensitive period" for human brain development. The parietal lobes undergo major changes from ages twelve to seventeen. Certain sub-areas may double or triple in size. The frontal lobes, a big chunk of "gray matter," are the last area to mature, undergoing dramatic changes. Gray matter (brain cells) thickens first (between ages eleven to thirteen) and later thins (reduces 7 to 10 percent) between the ages of thirteen and twenty. In 1999, Jay Giedd and colleagues demonstrated a growth spurt of gray matter in the teen brain.34 As the child spends more time learning, the brain's dendrites continue to make more connections.
This is followed by massive pruning, in which about 1 percent of gray matter is pared down each year during the teen years, while the total volume of white matter ramps up. Gray matter is overall brain tissue, white matter is the fatty coating on the axons called myelin that speeds up connectivity. It's a bit like the insulating rubber coating on electrical cords that protects raw wires from exposure. MRI results suggest that the thickening of gray matter is due to massive changes in synaptic reorganization, meaning more usage and more connections.35 These cells become highly receptive to new information. But they're not excited for the long term—the teen brain is not ready for that yet. Larger delayed rewards are valued less than smaller immediate rewards in impulsive individuals. Adolescents' sensitivity to rewards is stronger than that of adults. As a result, kids seek higher levels of novelty and stimulation to achieve the same feeling of pleasure. Risk, rewards, and fun are driving their brains. Keep that in mind with teens; they're terrible at risk management. In fact, their peers make too many decisions ("group think") because, collectively, no one can make up his or her mind except, often, the more impulsive ones. It's almost as if mother nature wanted teens to explore risky things and make babies.
But while this nearly exploding brain has more choices, it is often paralyzed by inefficiency. Just as with infants, it's the thinning back of synapses that creates more efficient decision making. Think of the metaphor of traveling through a dense forest; it's more efficient with a wide, paved road than with a machete, clearing underbrush on foot. Typically, the myelination process pushes back maturing until somewhere between ages sixteen and twenty, and often this extends into the late twenties. Elizabeth Sowell's work at UCLA suggests that the frontal lobes of girls mature faster than those of boys during puberty.36 But both genders are generally poor at reading and interpreting emotions. Their frontal lobes are still too immature to damp down impulsive responses to the emotions, usually generated from the emotional "smoke detector" we call the amygdala.
Generally, girls "connect the dots" earlier than boys in both emotional and cognitive functions. While most brains become physically mature between the ages of eighteen and thirty, it takes boys until about age twenty-four to catch up to girls' brain development. Using the frontal lobes for self-regulation, teens slowly (way too slowly for most adults who live and work with them) learn about interrupting a risky behavior, thinking before acting, and choosing among different courses of action. Unfortunately, the much-needed maturation of neural networks governing self-regulation hasn't happened in adolescence. These processes suggest that the "under construction brain" areas may be highly unstable, volatile, and unpredictable. The result is that they have a very high risk rate for accidents and injuries.
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