Although it was proposed over a century ago that feedback from facial expressions influence emotional experience, tests of this hypothesis have been equivocal. Here we directly tested this facial feedback hypothesis (FFH) by comparing the impact on self-reported emotional experience of BOTOX injections (which paralyze muscles of facial expression) and a control Restylane injection (which is a cosmetic filler that does not affect facial muscles). When examined alone, BOTOX participants showed no pre- to posttreatment changes in emotional responses to our most positive and negative video clips. Between-groups comparisons, however, showed that relative to controls, BOTOX participants exhibited an overall significant decrease in the strength of emotional experience. This result was attributable to (a) a pre- versus postdecrease in responses to mildly positive clips in the BOTOX group and (b) an unexpected increase in responses to negative clips in the Restylane control group. These data suggest that feedback from facial expressions is not necessary for emotional experience, but may influence emotional experience in some circumstances. These findings point to specific directions for future work clarifying the expression-experience relationship.
