U. TEXAS-AUSTIN (US)—Biology may be to blame when it comes to adolescents making stereotypically poor decisions and engaging in risky behavior.

“Risky behaviors, such as experimenting with drugs or having unsafe sex, are actually driven by over activity in the mesolimbic dopamine system, a system which appears to be the final pathway to all addictions in the adolescent brain,” says Russell Poldrack, professor of psychology and neurobiology at University of Texas, Austin.

Previous studies have found that teenagers tend to be more sensitive to rewards than either children or adults.

Now, Poldrack and fellow researchers have taken the first major step in identifying which brain systems cause adolescents to have these urges and what implications these biological differences may hold for rash adolescent behavior.

These findings were published online in the journal Nature Neuroscience.

Poldrack used functional Magnetic Resonance Imaging technology (fMRI) to study the brain activity of participants ranging in age from 8 to 30 who performed a learning task in which they categorized an abstract image into one of two categories.

Participants were given feedback displaying the correct response. To ensure motivation, they were given monetary rewards for each correct answer.

What the researchers were most interested in, however, was how each participant’s brain responded to “reward prediction error” (or the difference between an expected outcome of an action and the actual outcome) as they learned to categorize the images.

“Learning seems to rely on prediction error because if the world is exactly as you expected it to be, there is nothing new to learn,” Poldrack explains.

Previous research has shown that the dopamine system in the brain is directly responsive to prediction errors.

Researchers measured so-called positive prediction error signals in the participants’ brains as the participants discovered the results of their answers and the size of their rewards. Teenagers showed the highest spikes in these prediction error signals, which likely means they had the largest dopamine response.

Dopamine is known to be important for the motivation to seek rewards. It follows, then, that the greater prediction error signals in the adolescent brain could result in increased motivation to acquire more positive outcomes, and therefore greater risk-taking.

Poldrack says future studies will further explore the biological reasons for stereotypical adolescent behavior.

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