The psychostimulant
drug ±3,4-methylenedioxymethamphetamine (
MDMA) reportedly produces distinctive feelings of empathy and closeness with others.
MDMA increases social behavior in animal models and has shown promise in
psychiatric disorders, such as
autism spectrum disorder (ASD) and
post-traumatic stress disorder (
PTSD). How it produces these prosocial effects is not known. This behavioral and psychophysiological study examined the effects of
MDMA, compared with the prototypical stimulant
methamphetamine (MA), on two measures of social behavior in healthy young adults: (i) responses to socially relevant, "affective" touch, and (ii) visual attention to emotional faces. Men and women (N = 36) attended four sessions in which they received
MDMA (0.75 or 1.5 mg/kg), MA (20 mg), or a placebo in randomized order under double-blind conditions. Responses to experienced and observed affective touch (i.e., being touched or watching others being touched) were assessed using facial electromyography (EMG), a proxy of affective state. Responses to emotional faces were assessed using electrooculography (EOG) in a measure of attentional bias. Subjective ratings were also included. We hypothesized that
MDMA, but not MA, would enhance the ratings of pleasantness and psychophysiological responses to affective touch and increase attentional bias toward positive facial expressions. Consistent with this, we found that
MDMA, but not MA, selectively enhanced ratings of pleasantness of experienced affective touch. Neither
drug altered the ratings of pleasantness of observed touch. On the EOG measure of attentional bias,
MDMA, but not MA, increased attention toward happy faces. These results provide new evidence that
MDMA can enhance the experience of positive social interactions; in this case, pleasantness of physical touch and attentional bias toward positive facial expressions. The findings are consistent with evidence that the prosocial effects are unique to
MDMA relative to another stimulant. Understanding the behavioral and neurobiological processes underlying the distinctive social effects of
MDMA is a key step to developing the
drug for
psychiatric disorders.