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Rebels With a Cause

Studies of Adolescents' Brains Find Possible Physiological Basis for Turbulent Teenage Emotions

June 25, 1998|ROBERT LEE HOTZ | TIMES SCIENCE WRITER

Brain scans of healthy adolescents reveal for the first time what many parents have long suspected--that teenagers don't think or feel the same way as adults, in part, because their brains actually work differently.

The researchers discovered that teenagers not only process emotions more intensely and more indiscriminately than adults, but also appear to use their brains differently to handle what they are told.

The new findings suggest a possible physiological basis for the emotional turbulence of adolescence and the gulf of misunderstanding that sometimes separates the generations.

"It has implications for how we deal with adolescents and how we think about communicating with them," said Deborah Yurgen-Todd, director of neuro-psychology and cognitive neuro-imaging at McLean Psychiatric Hospital in Belmont, Mass. She recently presented her findings during a conference at the Whitehead Institute for Biomedical Research in Cambridge, Mass.

"Instead of assuming that they are young adults and fully formed in terms of their brain function," she said, "it means that we probably need to assume they are not always understanding what we are telling them verbally and they may not appreciate the consequences of their behavior."

These findings may come as some relief to those adults who simply assumed that teenagers were too rebellious or stubborn to pay attention to well-intended warnings about safe driving, study habits, unprotected sex or any other parental prescription for well-being.

Now there is evidence that something structural also is at work in the adolescent brain.

A flood of insights into how the mind works, based in large part on new neural imaging techniques, has given scientists a growing appreciation for how much the brain is physically transformed over a lifetime.

Pioneering research, for example, shows that between the ages of 3 and 8, a child's brain has twice as many neurons, twice as many connections between them and is twice as energetic as an adult brain. As the brain matures, those billions of neural connections are ruthlessly pruned into a mature form. Some synapses are reinforced by the stimulation of experience, while others atrophy through inattention.

At the peak of neural development, unused synapses are eliminated at a rate of thousands per second.

Only now, however, with the aid of noninvasive imaging schemes, are researchers able to analyze how such profound physical changes in brain structure can translate into subtle emotional behavior or affect cognitive development.

In a pair of brain studies conducted at the McLean Hospital Brain Imaging Center, Yurgen-Todd and her colleagues used functional magnetic resonance imaging to strip the roller coaster of the adolescent mind down to its fundamental machinery of neurons, synapses and biochemicals.

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They examined how 16 young people, between the ages of 9 and 17, and 24 adults, between the ages of 20 and 40, handled different mental tasks involving emotion and language.

They focused on the activity in two regions of the brain: the frontal lobe, a center of reason that scientists believe has a tempering effect on behavior, and a complex structure located in the brain's temporal lobe called the amygdala, a more primitive part of the brain that seems to be the seat of fear.

The amygdala also is critical to the formation of emotional memories, research shows, and plays a role in forming intuitive social judgments, such as whether someone may be trustworthy.

By studying how each person responded to a series of faces expressing different emotions, the researchers found that when younger people process emotion, the level of brain activity in the amygdala is higher than the activity in the frontal lobe.

In the older test subjects, the pattern was reversed. Compared to the adolescents, the activity in the frontal lobe was stronger and the activity in the amygdala was weaker.

"These results suggest that adolescents are more prone to react with gut instinct when they process emotions, but that as they mature into early adulthood, they are more able to temper their instinctive gut reaction response with rational reasoned responses," Yurgen-Todd said.

Not only did the adolescents overreact in terms of involuntary mental activity, but they also could not correctly identify the emotions in the pictures they were shown.

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"This may explain in part why adolescents produce incongruous responses to emotional stimuli," she said.

The researchers also examined how the same people handled several tasks designed to test language development, such as counting aloud and making lists of words, while the brain scanner compiled a three-dimensional image of the neural anatomy and chemical activity.

Those tests revealed the same pattern of differences in brain activity between adolescents and adults.

The older the test subject, the more the activity in the temporal region decreased and the activity in the frontal lobe increased. Researchers said that suggests the rational part of the brain becomes increasingly involved in language production as a person matures.

The researchers also found that the way the brain activity changed with age seemed to be associated with changes in the actual structure of the brain that also come with age, such as the growth in the volume of the brain's white matter relative to its gray matter during childhood and adolescence.

"If studies continue to produce this kind of data, it has very important implications for people who, say, give directions to 14-year-olds and don't understand why they are not followed," Yurgen-Todd said.

"In fact, they probably are not hearing the directions in the way you think they are."

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