The Neural Basis of Self-Touch in a Pain-Free Situation

Abstract

Objective:Self-touch is thought to be an act of coping with harmful or stressful situations, based on the mechanism which suppresses somatosensory perception as well as somatosensory cortex activity, and sympathetic activity. In addition, this suppression can be observed in even nonpainful and non-stressful situations. However, its detailed neural mechanism remains unknown. Several studied have shown, not only that the descending pain modulatory system (DPMS) plays critical roles in painful situations, but also that there is intrinsic functional connectivity in the DPMS in even non-painful situations. Based on these findings, we hypothesized that the neural system consisting of the anterior cingulate cortex (ACC), amygdala and rostral ventromedial medulla (RVM) would play a basic role in self-touch, and we here investigated interactive effects of these regions in a pain-free self-touch situation. Methods:We used functional magnetic resonance imaging (fMRI) to investigate brain activity induced by mere self-touch (rubbing the left hand with the right) in a pain-free and stress-free situation, and carried out the Physio-Physiological Interaction (PPI) analysis to investigate the modulatory effects of brain activity. Results:PPI analysis showed that the rostral ACC (rACC) modulated activity in the RVM and left cerebellum (CB) via the right amygdala, such that the modulation linearly suppressed RVM and left CB activity. Furthermore, the latter was positively correlated with right primary somatosensory cortex (SI) activity. Moreover, we also showed that coherent activity in the bilateral secondary somatosensory cortex (SII) modulated activity of both the left temporoparietal junction (TPJ) and RVM, with the latter also suppressed by the modulation in a linear fashion. Conclusion:These findings suggest that self-touch exerts inhibitory effects on sensory afferents and sympathetic activity through the ACC-amygdala-RVM (AAR) system, and that bilateral sensorimotor integration plays an important role in the effect based on the bodily self.

Distinction of self-produced touch and social touch at cortical and spinal cord levels

“…Previous brain-imaging studies on self–other distinction in the tactile domain are inconsistent, reporting weaker activation (16), deactivation (18), and even stronger activation during self-produced tactile stimulation (23). However, these early studies are constrained by small sample sizes ( n = 8–12).…”

“…A consequence of this cancellation is the observation that people cannot tickle themselves (15). The suggested mechanism for this phenomenon is an attenuation of cortical sensory processing (16–18). Such attenuation has been found for auditory and visual processing (19–21).…”

Gentle Touch Opens the Gate to the Primary Somatosensory Cortex

“…Thus, whether similar neural mechanisms are activated with mild tactile stimulation such as affiliative and gentle touch remains unconfirmed. A recent fMRI study has shown that there is intrinsic functional connectivity in the DPMS in non-painful situations [46], and another one has shown that self-touch activates the DPMS in a pain-free and stress-free situation [47]. These studies may support the possibility that the DPMS regulates somatosensory afferents based on their emotive valence, even for mild somatosensory stimuli with subtly different movement patterns.…”

“…Moreover, the DPMS can function even in the absence of painful/stressful stimulation, because intrinsic functional connectivity among DPMS regions (including the ACC and RVM) has been demonstrated in such situations [46]. Moreover, the DPMS is activated during self-touching behaviors in pain-free and stress-free situations [47].…”

“…Scanning was conducted with a 3.0T MRI system (Achieva Quasar Dual, Philips [47]. ROIs with a radius of 5 mm were set for each contrasts of C vs. baseline and BF vs. baseline.…”