On the mutual effects of pain and emotion: facial pain expressions enhance pain perception and vice versa are perceived as more arousing when feeling pain.

Perception of emotional stimuli alters the perception of pain. Although facial expressions are powerful emotional cues - the expression of pain especially plays a crucial role for the experience and communication of pain - research on their influence on pain perception is scarce. In addition, the opposite effect of pain on the processing of emotion has been elucidated even less. To further scrutinize mutual influences of emotion and pain, 22 participants were administered painful and nonpainful thermal stimuli while watching dynamic facial expressions depicting joy, fear, pain, and a neutral expression. As a control condition of low visual complexity, a central fixation cross was presented. Participants rated the intensity of the thermal stimuli and evaluated valence and arousal of the facial expressions. In addition, facial electromyography was recorded as an index of emotion and pain perception. Results show that faces per se, compared to the low-level control condition, decreased pain, suggesting a general attention modulation of pain by complex (social) stimuli. The facial response to painful stimulation revealed a significant correlation with pain intensity ratings. Most important, painful thermal stimuli increased the arousal of simultaneously presented pain expressions, and in turn, pain expressions resulted in higher pain ratings compared to all other facial expressions. These findings demonstrate that the modulation of pain and emotion is bidirectional with pain faces being mostly prone to having mutual influences, and support the view of interconnections between pain and emotion. Furthermore, the special relevance of pain faces for the processing of pain was demonstrated.