Common and distinct neural mechanisms associated with the conscious experience of vicarious pain

Vicarious pain perception has been an influential paradigm for investigating the social neuroscience of empathy. This research has highlighted the importance of both shared representations (i.e. overlap between representations involved in experiencing first-hand physical pain and observing pain) and mechanisms that discriminate between self and other. The majority of this research has been conducted in healthy younger adults using a group-average approach. There are, however, known inter-individual difference factors that can contribute to vicarious experience. One factor relates to the degree to which individuals experience explicit (i.e. conscious) versus implicit vicarious experience. Here we conduct the first systematic investigation of the neural basis of conscious vicarious pain in a large sample of participants. Using cluster analysis, we firstly demonstrate that consciously experiencing the pain of others is surprisingly prevalent and, exists in two forms: one group experiences sensory and localised pain whilst the other group report affective and non-localised experiences. Building on this, we used electroencephalography (EEG) and structural brain imaging to examine the neural correlates of vicarious pain in the three different groups. We find that the dominant electrophysiological marker used to index vicarious pain in previous studies was only found to be significant in the sensory and localised pain responder group. That is to say that when accounting for inter-individual variability in vicarious pain experience we only see modulation of the mu rhythm range in people that experience conscious first-hand pain on their own body that matched the location of observed pain to others. Finally, using voxel-based morphometry we identify a common difference in all groups that show conscious vicarious experience relative to typical adults; namely reduced grey matter in the right temporal-parietal junction (rTPJ). We suggest that this reflects a reduced ability to distinguish bodily self and other, and may be a common factor distinguishing conscious from unconscious vicarious experience.