Teen brains show less activity in the regions associated with motivation, reveals a brain imaging study.

And adolescents may be more willing to engage in dangerous activities such as drunk driving because this crucial part of their brain is under-developed, the US researchers suggest.

Teen risk-taking is much higher than in adults - teenagers are more likely to abuse drugs and alcohol and take sexual risks - but the reasons for it are hotly debated. Now researchers at the US National Institute on Alcohol Abuse and Alcoholism have found evidence for a difference in brain chemistry in a part of the brain involved in calculating risk and reward.

In adolescents, this part of the brain, known as the right ventrial striatum, appears to be under-active, says James Bjork, who led the small study. Perhaps teens seek more extreme behaviours to achieve normal levels of stimulation in this brain region, he suggests.

Bjork and colleagues carried out brain scans on 12 teenagers and 12 adults while they played a specially designed gambling game, where they were given differing financial incentives to hit a target.

Although teens and adults rated the rewards equally when questioned and hit the targets with equal frequencies, their brain scans showed a different story. The right ventral striatum in the adolescents showed significantly less activity than that of the adults.

"It appears that the brain circuitry in motivation to get rewards is under-engaged in teenagers and so it explains why they need extreme stimuli to achieve the same level of brain activity.

"The difference in activity may be exaggerated when the reward is not instant, which may explain why teenagers have difficulties achieving long-term goals. The next step is to study teen reactions to delayed rewards," Bjork told New Scientist.

(source:http://www.newscientist.com/news/news.jsp?id=ns99994718)

(Note: Inferences the press derived from this publication ranged from ridiculous (e.g., see http://www.rushlimbaugh.com/home/daily/site_022604/content/stack_d.guest.html) to the somewhat accurate (e.g., http://drkoop.com/template.asp?page=newsdetail&ap=93&id=517628). This story falls somewhere in the middle. -BK