The interactive effects of peers and alcohol on functional brain connectivity in young adults.

Alcohol and peer influence are known to have independent effects on risky decision making. We investigated combined influences of peers and alcohol on functional brain connectivity and behavior. Young adults underwent fMRI while completing response inhibition (Go/No-Go) and risky driving (Stoplight) tasks. Intoxicated participants made more mistakes on Go/No-Go, and showed diminished connectivity between the anterior insular cortex (AIC) and regions implicated in executive function (e.g., dorsal anterior cingulate). During the Stoplight game, peer observation was associated with increased connectivity between the AIC and regions implicated in social cognition (e.g., ventromedial prefrontal cortex). Alcohol and peers also exerted interactive influences, such that some connectivity changes only occurred when participants were observed by peers and under the influence of alcohol. These findings suggest that brain systems underlying decision making function differently under the combined influence of alcohol and peers, and highlight mechanisms through which this combination of factors is particularly risky for youth.