Power of Self-Touch: Its Neural Mechanism as a Coping Strategy

Self-touch is an act of coping with harmful or stressful situations based on suppression of somatosensory perception, somatosensory cortex activity, and sympathetic activity; however, the detailed neural mechanism remains unknown. Several studies have shown that the descending pain modulatory system (DPMS) plays critical roles in painful situations and that intrinsic functional connectivity in the DPMS is observed in even non-painful situations. Therefore, we hypothesized that the neural system consisting of the anterior cingulate cortex, amygdala, and rostral ventromedial medulla (RVM) would play a basic role in self-touch. We thus investigated the interactive effects of these regions in a pain-free self-touch situation. Functional magnetic resonance imaging was used to investigate brain activity induced by mere self-touch (rubbing the left hand with the right), and the physio-physiological interaction analysis was performed to investigate the modulatory effects of brain activity. Physio-physiological interaction analysis showed that the rostral anterior cingulate cortex modulated neural activity in the RVM and left cerebellum (CB) via the right amygdala, and the modulation linearly suppressed the RVM and left CB activity. Furthermore, the left CB activity was positively correlated with the right primary somatosensory cortex activity. Moreover, our study showed that coherent activity in the bilateral secondary somatosensory cortex modulated the activity of the left temporoparietal junction and RVM, and the RVM was suppressed in a linear manner. These results suggest that self-touch is a kind of passive avoidance automatically realized in the human brain to protect the self.