Teen Behavior Reflects Teen Brain

Last Editorial Review: 2/26/2004

The reward center in an adolescent's brain is not fully developed and is not as responsive as the reward center in adults. This may explain why teens are more apt to drink too much alcohol, use drugs or engage in unsafe sex, because these foolhardy activities require little effort for what seems like a greater reward.

Comment: It is one thing for all of us to know the teen brain is different. And it is remarkable that there is lower activation of the right ventral striatum centered in the nucleus accumbens. But WHAT DO WE DO about how our teenager (or someone else's) is behaving these days?

Barbara K. Hecht, Ph.D.
Frederick Hecht, M.D.
Medical Editors, MedicineNet.com

For related information on teens, please visit the MedicineNet.com Teen Center.

Adolescent Brains Show Reduced Reward Anticipation

Adolescents show less activity than adults in brain regions that motivate behavior to obtain rewards, according to results from the first magnetic resonance imaging (MRI) study to examine real-time adolescent response to incentives. The study also shows that adolescents and adults exhibit similar brain responses to having obtained rewards.

Researchers in the Laboratory of Clinical Studies of the National Institute on Alcohol Abuse and Alcoholism (NIAAA), one of the National Institutes of Health (NIH), conducted the study, which appears in the February 25 issue of the Journal of Neuroscience.

"Understanding adolescent motivation is critical for understanding why so many young people drink alcohol and engage in associated behaviors such as drinking and driving and sexual risk-taking. That understanding also will be critical for shaping prevention messages that deter such behaviors," said Ting-Kai Li, M.D., Director, NIAAA. "With today's report, researchers in NIAAA's Laboratory of Clinical Studies provide an important part of the picture."

In the MRI study, James Bjork, Ph.D., and others in the laboratory of Daniel Hommer, M.D., scanned the brains of twelve adolescents aged 12 to 17 years and twelve young adults aged 22 to 28 years. While being scanned, the subjects participated in a game-like scenario risking monetary gain or loss. The participants responded to targets on a screen by pressing a button to win or avoid losing 20 cents, $1, or $5.

For both age groups, the researchers found that the anticipation of potential gain activated portions of the ventral striatum, right insula, dorsal thalamus, and dorsal midbrain, with the magnitude of ventral striatum activation sensitive to gain amount. In adolescents, however, the researchers found lower activation of the right ventral striatum centered in the nucleus accumbens, a region at the base of the brain shown by earlier research to be crucial for motivating behavior toward the prospect of rewards.

"Our observations help to resolve a longstanding debate among researchers about whether adolescents experience enhanced reward from risky behaviors - or seek out alcohol and other stimuli because they require enhanced stimulation. They also may help to explain why so many young people have difficulty achieving long-term goals," according to James Bjork, Ph.D., first author on the study.

When the researchers examined brain activity following gain outcomes, they saw that in both adolescents and young adults monetary gain similarly activated a region of the mesial frontal cortex. "These results suggest that adolescents selectively show reduced recruitment of motivational but not consummatory components of reward-directed behavior," state the authors.

Source: National Institutes of Health (www.nih.gov)


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