Synchronal dual brain stimulation over the somatosensory cortex modulated social touch-induced analgesia depending on empathy.

Social touch, when provided as emotional support, can induce pain relief. Alpha inter-brain synchrony in the somatosensory cortex may be a neural factor contributing to the pain relief induced by social touch. This study investigated whether artificial manipulation of inter-brain communication in the pain-receiver and touch-giver could modulate touch-induced analgesia using transcranial alternating current stimulation. Sixteen same-sex pairs of participants were assigned the roles of pain-receiver and touch-giver during alpha-band transcranial alternating current stimulation applied to the somatosensory cortex. Three transcranial alternating current stimulation conditions were randomized, and the participant roles changed between sessions: (1) the pain-receiver received transcranial alternating current stimulation and the touch-giver received sham stimulation; (2) both received transcranial alternating current stimulation (hyper-transcranial alternating current stimulation); and (3) both received sham stimulation. Social touch reduced pain, although there were no significant differences in pain perception among the three conditions. Analgesia by social touch during hyper-transcranial alternating current stimulation, compared with sham transcranial alternating current stimulation, was negatively correlated with the empathy level of the pain-receiver. No relationship was observed between pain relief and empathy levels when transcranial alternating current stimulation was administered only to the pain-receiver. Hyper-transcranial alternating current stimulation aimed to enhance alpha-band synchrony between dyads could promote touch-induced analgesia, especially in pain-receivers with low emotional empathy. These findings indicate a possible association between synchrony of somatosensory alpha activity and pain relief through social interactions. Manipulating brain synchrony by considering a patient's empathy level may support therapeutic analgesia influenced by the clinician-patient relationship. PERSPECTIVE: This study provides preliminary evidence for a possible association between alpha inter-brain synchrony in the somatosensory cortex and touch-induced analgesia from temporarily altering brain oscillations using hyper-transcranial alternating current stimulation. Manipulating inter-brain synchrony while considering a patient's empathy level may enhance therapeutic analgesia influenced by the clinician-patient relationship.