ficity for targeting brain regions heavily innervated by the midbrain dopamine system. Other recent research has suggested that dopamine may play a role in the learning of behaviors associated with reward and pleasure. Consistent with this view, the model demonstrated that when the rewards were administered in an unpredictable manner, a key reward structure of the brain--the striatum--was more active, suggesting that "reward" to the brain may have more to do with the predictability of an event than with how pleasurable it is.

"These studies suggest that adolescent decisions may, in part, be due to a greater biological sensitivity to either rewards themselves or, more likely, the novelty of rewards," says Berns. "It is possible that a reward or novelty associated with the reward may trigger hyperactivity in still developing brain reward structures and circuits."

Another study found differences in risk-taking behaviors in pubescent rats. Georgia Hodes, a graduate student at Rutgers University working with Tracey J. Shors, PhD, used an elevated plus maze to study exploratory behavior of male and female rats before, during, and after puberty. The maze contained "safe" (closed and darker) areas and more "anxiety-provoking" (open and exposed) areas. The researchers analyzed videotapes of rats as they maneuvered freely through the maze during 10-minute sessions. The elevated plus maze is a task used to measure anxiety, which is created by the conflict between the animal's desire to explore and its fear of open spaces. An animal's entering the exposed areas of the maze indicates lower anxiety, while extension of the rat's head into the open area without actually entering it (stretched attenuated posture) indicates assessment of risk.

The researchers found that both male and female pubescent rats were more likely to enter and spent more time in the open and exposed areas than did the adult male and female rats, suggesting that
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Contact: Leah Ariniello
dawn@sfn.org
202-462-6688
Society for Neuroscience
24-Oct-2004

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