Research shows why a teen brain incapable of reasoning like an adult's

Teens driven to distraction
By Ronald Kotulak, Chicago Tribune science reporter
Published March 24, 2006
By the time puberty is over in the middle to late teens, when adult height and full reproductive capacity have been achieved, the body is at its peak--the strongest, swiftest and healthiest it will ever be. But the brain lags behind, laboring to adapt to the most complex society that has existed. This mismatch--between a fully grown body and an immature brain that is trying to cope with emotions, sexual urges, poor judgment, thrill seeking and risk taking--is a key factor making motor vehicle accidents the No. 1 cause of death among adolescents and young adults, followed by murder and suicide.

Using powerful new imaging technology to look inside the brain, scientists are beginning to unravel the biology behind this critical period of development. They are finding that an adolescent's brain undergoes a previously unsuspected biological makeover--a massive growth of synaptic connections between brain cells.This spectacular surge kicks off an extensive renovation of the brain that is not complete until the mid-20s. Scientists say the resulting learning curve, when teens struggle to shed childish thoughts for adult ones, is why adolescence is such a prolonged and perilous journey for so many.It helps explain not only why teens are more prone to crash a car than at any other time of life, but why they are more likely to engage in risky sex, drug abuse or delinquency. Although teens often can think as logically as an adult, the process can be easily derailed by flaring emotions or other distractions."The reason that kids take chances when they drive is not because they're ignorant," said Temple University psychologist Laurence Steinberg. "It's because other things undermine their better judgment."

The synaptic growth spurt that occurs in puberty is similar to the ones that occur after birth, when the brain first begins to learn. The early exposure to the outside world enables the brain to connect to the body, developing its capacity for processing sound, sight, smell, touch and taste, and to make sense of them.Learning occurs only after excess synapses not stimulated by experience are eliminated, much like the pieces of marble that have to be chipped away to create a work of art.

Now scientists have found that a second wave of growth and pruning occurs in adolescence. Synapses that are not incorporated into neural networks for memory, decision-making and emotional control are eliminated to make way for a leaner, more efficient brain.This late blossoming of synapses, it is thought, provides the brain with a new capacity for learning and allows the brain to make the transition from childhood to adulthood.

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