Emotional faces alter pain perception

Background Although emotional faces might be particularly suited for the investigation of emotional pain modulation, they have thus far rarely been used. In particular, previous studies using emotional faces for pain modulation did not assess modulation of mood, did not differentiate pain intensity and unpleasantness, and did not investigate the interaction with attentional state. Here, we assessed how viewing emotional faces impacts the perceived intensity and unpleasantness of experimentally induced pain as well as subjects' mood. Methods Healthy subjects viewed sad, happy or neutral faces, and short painful thermal stimuli were simultaneously applied to the volar forearm. Subjects provided ratings of pain intensity, pain unpleasantness and mood after blocks consisting of eight pairs of thermal stimuli and eight pairs of faces. Each subject viewed six blocks in total (two of each emotion). Perceptual discrimination tasks ensured that subjects either focused on the pain or on the emotional faces. Results Subjects reported higher pain unpleasantness and higher pain intensity as well as worse mood when they viewed blocks of sad faces compared with blocks of happy or neutral faces. Changes in mood correlated with modulation of pain intensity, but not unpleasantness. No interaction was observed between emotional pain modulation and attentional state. Conclusions These results provide evidence that viewing emotional faces modulates perceived pain intensity and unpleasantness and that this pain modulation is related to mood changes, at least for intensity. Faces might be a reliable and socially relevant tool to study the impact of discrete emotions on pain perception.