SciFri 3.25.05: The adolescent mind

An immature prefrontal cortex may explain why, for example, a teen who knows better than to drink and drive may still do so when an adult might not.

The Biological Basis of 'That Awkward Age'

By Deane Morrison

Published on March 25, 2005

The word "teen" comes from Sanskrit and Indo-European roots meaning "pain" or "destroy." It's just one more reminder that the teen years are hard for everybody. And why not? It's a time when bodies are changing and responsibilities are increasing. But acting responsibly can be particularly tricky for teens.

Certainly, teens have less experience than adults in matters where good judgment is required. But although teens may have bodies that look adult, their brains are still changing, and this, combined with the fierce emotions and pressures of teendom, sometimes spells trouble.

The brain is like a factory that takes input from the senses and produces output in the form of behavior. In between, the brain generates memories, thoughts, moods, and emotions. The top floor of the factory is the prefrontal cortex, or PFC. According to psychology associate professor Monica Luciana, the PFC plays a major role in working memory--the kind you use to set and work toward goals. It can be as simple as holding the concept of "house keys" as you search for them or as complex as keeping track of all the cards in a game of blackjack. The PFC allows information to be integrated and emotionally controlled so you can accomplish goals.

But the PFC may not reach its full development until age 20 or higher, says Luciana. She notes that for adolescents, more than for adults, the ability to use information in working memory can be derailed by emotions. In other words, there's a reason why teens' heads are so often ruled by their hearts. An immature PFC may explain why, for example, a teen who knows better than to drink and drive may still do so when an adult might not.

A study at the University of Iowa followed changes in the brains of about 383 people ages 7 to 82, says Tonya White, an assistant professor of psychiatry. Using brain imaging techniques, the researchers found that the cerebral cortex as a whole undergoes huge development, and that the areas of the cortex associated with vision experience it early on. This development is not growth, however; the gray matter of the cortex thins as the brain becomes more efficient. The rate of change drops with age, usually starting its slowdown between ages 15 and 25.

Connections between brain cells also undergo lots of rearrangement.

"In adolescents, connections are becoming more refined," says White. "It's a 'use it or lose it' situation." In an analogy she developed with child development professor Charles Nelson, if the brain were laying out roads, it would first lay them out all over with exit ramps and transfer points everywhere. Certain brain pathways would be like the LA to Chicago route--they would be indispensable in every person, and genetically ordained. But other routes would have to get "traffic," or they would be pulled up, a change that allows greater efficiency in processing information.

A clear example of such pruning occurs in language acquisition. Neurons are tuned to certain sounds, and if a young person is exposed to the sounds, the neurons are maintained. In White's own case, living in Germany at an early age helped her speak without an accent when she returned to Germany as a student many years later, even though she never actually spoke much German during the years of "incubation."

The white matter of the brain, what White calls "the high-speed broadband" of brain communication, continues to develop into the mid-30s. White matter consists of nerve fibers that allow one cell to pass messages to another, and its development allows individuals to process information more efficiently. As the arrangements of nerve fibers continues to mature, people are more able to manipulate information in ways that help control emotion and keep people on task--what brain scientists call higher-order cognitive functions.

As all these changes are taking place, teens must deal with a whole new set of circumstances related to finding and assuming their place in society. With certain parts of the brain--notably the frontal cortex--still not in their adult state, teens may rely more on the parts of the brain that deal with emotions (called the limbic system) to make decisions. Unfortunately, there's a great deal of variability in how adolescents regulate their emotions, and this can make it hard to predict which adolescents will, as adults, have problems with emotionally based behavior.