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Harvard Commentaries
35320
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School


Minding Your Mind Minding Your Mind
 

Understanding the Adolescent Brain


October 24, 2012

By Michael Craig Miller M.D.

Harvard Medical School


It's a good thing parents get 12 years to bond with their children before they become teenagers. Otherwise they might not be so motivated to help them grow into adults.

Teens are often annoying, demanding, moody, gloomy, and defiant. If their reckless behavior doesn't kill them, it may scare their parents to death. And parents are partially justified in being scared: it's a time when rates of addiction and mental disorders spike, along with the risk of accidental death, suicide, and homicide.

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A Messy Transition

Child development specialists say this angst-producing time may be a necessary—though messy—phase for adolescents to go through. The bond between parents and children can be so strong that we might never let go if we didn't live through a time that makes separation look pretty good.

It's an adolescent's job to become independent, explore limits, take risks, break rules, and rebel against the older generation. Powerful sexual impulses and romantic feelings emerge, too. Adolescents are keen to discover the world and create their own culture to replace the status quo.

This is also a time of contradiction. Though teenagers may trash their parents, they still need adult support and protection.

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Intellect or Emotion?

Regardless of the purpose of these behaviors, knowing something about the biology behind them may help everyone deal with this time more comfortably.

It's not that teens lack smarts. By age 15 or 16, adolescents do about as well as adults on tests of intellectual ability. But because they are far from being fully developed emotionally, they often forget to think. The thrill of driving fast, the adventure of diving into unknown waters, and the excitement of sex overwhelm their judgment.

Peer pressure is powerful, too. Teenagers can adamantly tell you they would never get into a car with a drunk driver, but come Saturday night, it may be embarrassing not to go along with their friends. Gang violence, reckless driving, and drinking get worse in groups. Unlike adults, adolescents take more chances when friends are watching.

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How the Teen Brain Becomes an Adult Brain

These differences between adolescents and adults have a basis in brain development. Throughout childhood, the brain undergoes dramatic changes. Nerve cells grow and they develop more connections. A substance called myelin covers the cells, increasing the speed of nerve signals about 100-fold. Finally, "pruning" occurs, which eliminates connections that are not needed. This makes communication more efficient from nerve to nerve, from circuit to circuit, and between the right and left sides of the brain.

Nerve connections evolve throughout life, but the biggest changes occur from birth to the early 20s. Each brain region undergoes the growing and pruning process at different times. Basic functions (the ability to smell, see or move) mature first. The areas responsible for more advanced tasks mature later. For example, the part of the brain that controls vision (the visual cortex) starts its burst of growth when a baby is 4 months old. By preschool, it has been pruned to its adult level. In contrast, the reasoning part of the brain (the prefrontal cortex) starts its growth spurt at age 3 or 4, and most pruning doesn't occur until middle or late adolescence. Among the last connections to mature are those between the prefrontal cortex and the "emotional" part of the brain (limbic system). Emotional learning and self-regulation depend on these links.

A circuit of particular interest is the one that links the reasoning parts of the brain to the brain's reward system. The weakness of this connection during adolescence may explain why teens are particularly prone to the power of addictive substances and romantic love. For example, adolescents become addicted to nicotine faster and at lower doses than adults do. And brain scans show that the brains of teenagers are much more sensitive to novel experiences compared to adult brains.

Hormones are at work, too. The adolescent brain pours out stress hormones, sex hormones, and growth hormone, which in turn influence brain development. Testosterone production goes up 10-fold in adolescent boys. Sex hormones act in parts of the brain that are important for the regulation of arousal and mood.

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Helping an Adolescent Grow Up

A fundamental aim for adolescents and the adults in their lives is to tolerate the inevitable exasperation on both sides. Research supports using a parenting style that avoids extremes of punishment and permissiveness, though it's difficult to define those terms in practice.

The adolescent—and his or her brain—need the opportunity to be independent, but at times they need structure, too. Here are a few guidelines to get you started.

  • Be warm but not lax.
  • Be firm but not harsh.
  • Accept the adolescent's increasing need for independence.
  • Avoid trying to control what you have limited power to control.
  • Show, don't tell. If teens see you being loving, generous, industrious, and sincerely committed (to people, work and hobbies), it will mean more than a lecture.
  • Focus your attention on the riskiest behavior: any combination of drinking and driving, drug use that impairs judgment and might put them at grave risk, irresponsible sexual activity (especially leading to illness or an unwanted pregnancy).

You can't avoid the turbulence that is a normal part of biological growth. So don't try. Instead, understand how the adolescent brain evolves and create conditions where that brain can grow into the best it can be! You might find it is more fun and the relationship with the teens in your life may become more satisfying.

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Michael Craig Miller, M.D., is the Editor in Chief of the Harvard Mental Health Letter. He is also associate physician at Beth Israel Deaconess Medical Center and assistant professor at Harvard Medical School. He has been practicing psychiatry for more than 25 years and teaches in the Harvard Longwood Psychiatry Residency Program.

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