Teenagers more susceptible to addiction and depression

Pitt research team finds region in the adolescent brain associated with learning and habit formation highly responsive to reward

Teenagers are more susceptible to developing disorders like addiction and depression, according to a paper published by Pitt researchers Jan. 16 in the Proceedings of the National Academy of Sciences.

The study was led by Bita Moghaddam, coauthor of the paper and a professor of neuroscience in Pitt's Kenneth P. Dietrich School of Arts and Sciences. She and coauthor David Sturman, a MD/PhD student in Pitt's Medical Scientist Training Program, compared the brain activity of adolescents and adults in rats involved in a task in which they anticipated a reward. The researchers found increased brain cell activity in the adolescent rats' brains in an unusual area: the dorsal striatum (DS)-a site commonly associated with habit formation, decision-making, and motivated learning. The adult rats' DS areas, on the other hand, did not become activated by an anticipated reward.

"The brain region traditionally associated with reward and motivation, called the nucleus accumbens, was activated similarly in adults and adolescents," said Moghaddam. "But the unique sensitivity of adolescent DS to reward anticipation indicates that, in this age group, reward can tap directly into a brain region that is critical for learning and habit formation."

Typically, researchers study the correlation between different behaviors of adolescents and adults. The Pitt team, however, used a method they call "behavioral clamping" to study if the brains of adolescents process the same behavior differently. To that end, the researchers implanted electrodes into different regions of rat adolescent and adult brains, allowing the researchers to study the reactions of both individual neurons and the sum of the neurons', or "population," activity.

The researchers' predictions proved accurate. Even though the behavior was the same for both adult and adolescent rats, the researchers observed age-related neural response differences that were especially dramatic in the DS during reward anticipation. This shows that not only is reward expectancy processed differently in an adolescent brain, but also it can affect brain regions directly responsible for decision-making and action selection.

"Adolescence is a time when the symptoms of most mental illnesses-such as schizophrenia and bipolar and eating disorders-are first manifested, so we believe that this is a critical period for preventing these illnesses," Moghaddam said. "A better understanding of how adolescent brain processes reward and decision-making is critical for understanding the basis of these vulnerabilities and designing prevention strategies."

The Pitt team will continue to compare adolescent and adult behavior, especially as it relates to stimulants-such as amphetamines-and their influence on brain activity.