Seeing the hand being touched modulates the primary somatosensory cortex

Recent behavioral studies have shown that viewing the stimulated body part can enhance tactile acuity. We examined effects of viewing the stimulated body part by using neuromagnetic source imaging. Study participants were covertly stimulated on their first digit (D1) while watching a video that showed a hand where D1 was stimulated. The video hand appeared in the region where the real hand would be expected. In addition, participants were stimulated on D1 without watching the video. The results demonstrated a shift of D1 to a more inferior position and an increase of the dipole strength of D1 during the observation of tactile stimulation. We discuss these cross-modal interactions with recent studies on visuotactile enhancement.