Dopaminergic and opioidergic regulation of implicit hedonic facial reactions during anticipation and consumption of social and nonsocial rewards

The observation of animal hedonic orofacial and behavioral reactions has played a fundamental role for the identification of a dopaminergic motivational, and an opioidergic hedonic component of reward. Translation to humans remains difficult, however, as human research has struggled to adopt a similar operationalization of reward. Here, we investigated the neurochemical basis of hedonic facial and behavioral reactions to different types of rewards in healthy adult volunteers, by pharmacologically reducing dopaminergic and opiodergic receptor-specific action. Subjective ratings, physical effort, and facial reactions to matched primary social (affective touch) and nonsocial (food) rewards were assessed. Both drugs resulted in reduced physical effort and increased negative facial reactions during reward anticipation, but only opioidergic manipulation caused reduced positive facial reactions during reward consumption. This suggest that facial reactions during anticipated and experienced pleasure rely on partly different neurochemical systems, providing novel evidence in support of existing theoretical models of reward.