Growing Brains Influence Adolescents' Behavior Raging Hormones Less of a Factor

The Florida Times Union, December 31, 2000 | Go to article overview
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Growing Brains Influence Adolescents' Behavior Raging Hormones Less of a Factor

Every parent dreads it.

Almost overnight a sweet, cheerful, obedient child mutates into a churlish monster prone to recklessness and unpredictable mood swings.

This is not The Exorcist. This is adolescence.

Parents and experts have always blamed the same hormones that catapult young bodies into adulthood for the sleeping until noon, the reckless driving, the drug use and the other woes of adolescence. But recent research shows that what's going on above teenagers' necks, not raging hormones, explains the changes.

Beginning around age 11, the brain undergoes major reorganization in an area associated with things like social behavior and impulse control. Neuroscientists figured this out only in the last few years, and the discovery has led them to see adolescence as a period when the developing brain is vulnerable to traumatic experiences, drug abuse and unhealthy influences.

"The adolescent brain is different. It's still growing," said Fulton Crews, a neuroscientist at the University of North Carolina in Chapel Hill.


Not long ago, neuroscientists thought the brain stopped growing by the time a child entered nursery school. By then, it was thought, nearly all the brain's wiring had been connected and the only remaining task was to program that hardware.

But new brain imaging technologies have shattered that notion. Using techniques like MRI and positron emission tomography, or PET scanning, researchers have detected brain growth throughout childhood and well into adolescence.

Because their brains are not yet mature, adolescents do not handle social pressure, instinctual urges and other stresses the way adults do. That may explain in part why adolescents are so prone to unsavory or reckless behavior.

"The adolescent brain is just in a different state than the adult brain," Crews says.

This year in the scientific journal Nature, researchers presented a series of time-lapse images depicting brain growth from age 3 to 15. The images showed a tangle of nerve cells sprouting in the part of the brain that sits above the eyes, then a period of "pruning" after puberty, when about half of the new fibers are cut away to create an efficient network of circuits.

All this action happens in a part of the brain known as the prefrontal cortex, an area responsible for what neuroscientists call the "executive functions." Those functions are practically a laundry list of the qualities adolescents often lack -- goal-setting, priority-setting, planning, organization and impulse inhibition.


Adolescence is a time of risk-taking, says Lynn Ponton, a psychiatrist at the University of California-San Francisco and author of The Romance of Risk: Why teenagers Do the Things They Do.

"A big part of adolescence is learning how to assess the risk in an activity," Ponton says. "Part of the reason teenagers aren't good at risk-taking is that the brain isn't fully developed."

Looked at that way, it is no big surprise that accidents are the leading cause of death among adolescents, or that teens are more likely to become crime victims than any other age group. It's no wonder that the vast majority of alcoholics and smokers get started during their teen years, or that a quarter of all people with HIV contract it before age 21.

It's no big secret that things like criminal records and sexually transmitted diseases can really mess up your life. But neuroscientists are learning that less serious stuff can have lasting effects, too.

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Growing Brains Influence Adolescents' Behavior Raging Hormones Less of a Factor


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