Repeated exposure to vicarious pain alters electrocortical processing of pain expressions.

Repeated exposure to others in pain has been shown to bias vicarious pain perception, but the neural correlates of this effect are currently not known. The current study therefore aimed at measuring electrocortical responses to facial expressions of pain following exposure to expressions of pain. To this end, a between-subject design was adopted. Participants in the Exposure group were exposed to facial expressions of intense pain, while the participants in the Control group were exposed to neutral expressions before performing the same pain detection task. As in previous studies, participants in the Exposure group showed a significantly more conservative bias when judging facial expressions pain, meaning that they were less inclined to judge moderate pain expressions as painful compared to participants in the Control group. Event-related potential analyses in response to pain or neutral expressions indicated that this effect was related to a relative decrease in the central late positive potential responses to pain expressions. Furthermore, while the early N170 response was not influenced by repeated exposure to pain expressions, the P100 component showed an adaptation effect in the Control group only. These results suggest that repeated exposure to vicarious pain do not influence early event-related potential responses to pain expressions but decreases the late central positive potential. These results are discussed in terms of changes in the perceived saliency of pain expressions following repeated exposure.