MRI Provides Insights into Adolescent Self-Control: Dorsolateral Prefrontal Cortex Activated

Article excerpt

PITTSBURGH -- The impulsivity, risk-taking, and poor decision-making of adolescence may reflect processes that optimize the brain to work at its best in adulthood, the results of studies comparing the behavior of adolescents and adults suggest.

Adolescents are capable of self-control but not in the consistent manner that adults enjoy, Beatriz Luna, Ph.D., said at the annual meeting of the Society for Developmental and Behavioral Pediatrics.

In a study of 245 people aged 8-30 years, Dr. Luna and her colleagues monitored the ability of subjects to control their eye movements. Individuals were instructed to look at light while in a dark room. When the first light was turned off, they were told to look away from a second light that appeared. The second part of the study reversed the situation by asking the subjects to look at the second light as quickly as possible once it appeared.

The study showed a dramatic decrease from childhood through adolescence and into adulthood in the failure to suppress looking at the second light when told to not look.

"We knew that in fact [children] understood the instructions quite well but were unable to inhibit this incredible tendency to look at the light," said Dr. Luna of the department of psychiatry at the University of Pittsburgh.

In subjects 14-15 years of age, the investigators began to see adult-level performance in the number of times errors were made in suppressing a response.

The results of functional MRI studies of similar eye movement tests have given researchers some insight into the brain circuitry that underlies the ability to inhibit a response. A widely distributed circuitry supports the inhibition of response in all ages, but specific regions of the brain, such as the frontal and parietal cortices and superior colliculus, become highly involved and collaborate in preparing a response as people become adults, Dr. Luna explained. Cellular studies have shown that the superior colliculus, for example, must be activated to a certain level to inhibit a response. "Without this, you will commit an error," she said.

In one functional MRI study involving 36 people aged 8-30 years, when subjects saw a central red plus sign on a screen, they were instructed to look to the other side of a screen, away from a new target. When they saw a green plus sign, the subjects were supposed to look at the subsequent target as quickly as possible.

During the task, children were "stuck" in just using the visual-spatial processing areas of the brain to make sense of the visual-spatial elements of the task, she noted.

Only adults used their lateral cerebellum. Adolescents were significantly activating the dorsolateral prefrontal cortex (DLPFC), which is often seen in functional MRI studies when the difficulty of a task is increased. The adolescents appeared to behave at the same level as adults in the functional MRI study, but it was much more difficult for them to do the task. (See photo). "Perhaps because [adolescents] cannot access the distant parts of the brain, they have to rely on [the DLPFC] to have cognitive control of behavior," Dr. …