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THURSDAY, Feb. 26 (HealthDayNews) -- Teenage behavior can leave parents shaking their heads and wondering what could possibly be motivating their adolescent's actions.

It turns out it actually takes quite a bit to motivate a teen, because the reward center in an adolescent's brain isn't fully developed and isn't as responsive as the reward center in adults.

That's the conclusion of a study in the Feb. 25 issue of the Journal of Neuroscience.

And these findings may explain why teens are more apt to drink alcohol, use drugs or engage in unsafe sex, because these activities require little effort for a seemingly greater reward.

"Adults have readily active motivation in the brain," says study co-author James Bjork, a research fellow in the laboratory of clinical studies at the National Institute on Alcohol Abuse and Alcoholism. But, he says, "it may take exceptionally strong incentives to get kids jazzed up."

Bjork and his colleagues compared MRI scans of 12 teenagers between the ages of 12 and 17 to MRI scans of 12 adults between the ages of 22 and 28. While undergoing the MRI scans, the study volunteers were asked to play a game. If they could hit a target on a screen, they were rewarded with 20 cents, $1 or $5. If they couldn't hit the target, they would lose money.

In both the teens and adults, the MRI images showed that in anticipation of a potential gain, the ventral stratium, right insula, dorsal thalamus and dorsal midbrain sections of the brain were activated. And the ventral stratium, which is believed to be a reward center in the brain, showed increased activation as the reward amount increased for both groups.

But, the right ventral stratium showed less activation in teens than in adults. According to Bjork, other research has shown this area of the brain is responsible for motivation.

"That region of the brain controls how much an organism is willing to work to get a reward," Bjork says. "The data show that adolescents are just as happy and excited at the prospect of winning as adults, but they differed in the expenditure of effort for that reward."

For parents, these findings show "there might be a normal developmental reason why it's so tough to get your teen off the couch," Bjork says. Additionally, he says, the findings could explain why teens are drawn to risky behavior such as alcohol and drugs, because they offer a strong reward for very little effort.

Dr. Ramon Solhkhah, director of child and adolescent psychiatry at St. Luke's-Roosevelt Hospital Center in New York City, says the findings "give us information about how teenagers prove rewards in a different way than adults do."

He says it's important to realize their brains are still developing, and they are not just small adults. Teens rarely consider long-term consequences, he says.

"Their sense of the future is processed differently than an adult's. It appears [teens] do much better with short-term consequences, so the high they get from using drugs may be more powerful than the potential long-term health consequences," Solhkhah explains.

He recommends telling your teen how things will affect him or her now, rather than in the future. Don't tell your child that smoking will give him lung cancer in 30 years, he says, because it won't mean anything to your teen. Instead, he says, focus on here and now. For example, tell your child how smoking can stain teeth or make it difficult to participate in athletics.

More information

The University of Minnesota's College of Human Ecology offers advice about your teen's behavior. The National Clearinghouse for Alcohol and Drug Information discusses the importance of setting rules for your teen.

(SOURCES: James Bjork, Ph.D., research fellow, laboratory of clinical studies, National Institute on Alcohol Abuse and Alcoholism, Bethesda, Md.; Ramon Solhkhah, M.D., director, child and adolescent psychiatry, St. Luke's-Roosevelt Hospital Center, New York City; Feb. 25, 2004, Journal of Neuroscience)

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