Somatosensory activity modulation during observation of other's pain and touch.

We examined whether somatosensory activity could be modulated by the observation of bodily experiences. For this purpose, somatosensory-evoked potentials elicited by non-painful stimulation were recorded when subjects were viewing a hand penetrated by a needle, touched by a cotton swab or at resting without stimulation. Participants were instructed to adopt an egocentric perspective when viewing the videos and to rate pain intensity and unpleasantness supposedly experienced by the model, as well as the unpleasantness induced by the video clips. Results indicated that pain videos were rated as more unpleasant than touch videos, and that observation of both pain and touch video clips led to a significant enhancement of P50 amplitudes as compared to viewing a hand without stimulation. Moreover, enhanced P50 amplitudes during observation of both pain and touch in others were associated with increased unpleasant ratings induced by the video clips, as well as with high scores in a perspective taking scale (IRI). These findings provide support for the involvement of an attentional bottom-up mechanism which could be responsible to enhance sensory processing of somatic information when observing bodily experiences in others irrespective of whether they are painful or not.