RATIONALE:

Drug users often report using drugs to enhance social situations, and empirical studies support the idea that drugs increase both social behavior and the value of social interactions. One way that drugs may affect social behavior is by altering social processing, for example by decreasing perceptions of negative emotion in others.

OBJECTIVES:

We examined effects of d-amphetamine on processing of emotional facial expressions and on the social behavior of talking. We predicted amphetamine would enhance attention, identification, and responsivity to positive expressions, and that this in turn would predict increased talkativeness.

METHODS:

Over three sessions, 36 healthy normal adults received placebo, 10, and 20 mg d-amphetamine under counterbalanced double-blind conditions. At each session, we measured processing of happy, fearful, sad, and angry expressions using an attentional visual probe task, a dynamic emotion identification task, and measures of facial muscle activity. We also measured talking.

RESULTS:

Amphetamine decreased the threshold for identifying all emotions, increased negative facial responses to sad expressions, and increased talkativeness. Contrary to our hypotheses, amphetamine did not alter attention to, identification of, or facial responses to positive emotions specifically. Interestingly, the drug decreased the threshold to identify all emotions, and this effect was uniquely related to increased talkativeness, even after controlling for overall sensitivity to amphetamine.

CONCLUSIONS:

The results suggest that amphetamine may encourage sociability by increasing sensitivity to subtle emotional expressions. These findings suggest novel social mechanisms that may contribute to the rewarding effects of amphetamine.