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Case LK, Laubacher CM, Richards EA, Spagnolo PA, Olausson HW, Bushnell MC (2017) Inhibitory rtms of secondary somatosensory cortex reduces intensity but not pleasantness of gentle touch. Neuroscience Letters, 653:84-91      
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• 1-Hz inhibitory rTMS was conducted over secondary somatosensory cortex (S2) or vertex. • rTMS over S2 decreased ratings of touch intensity for fast but not slow brushing. • rTMS over S2 did not alter touch pleasantness or tactile discrimination. • rTMS over S2 using the H8 deep TMS coil reduced somatosensory BOLD response in S2 but did not affect the insula. • Study results suggest that S2 is causally involved in the perception of touch intensity but not in touch pleasantness
Abstract
Research suggests that the discriminative and affective aspects of touch are processed differently in the brain. Primary somatosensory cortex is strongly implicated in touch discrimination, whereas insular and prefronal regions have been associated with pleasantness aspects of touch. However, the role of secondary somatosensory cortex (S2) is less clear. In the current study we used inhibitory repetitive transcranial magnetic stimulation (rTMS) to temporarily deactivate S2 and probe its role in touch perception. Nineteen healthy adults received two sessions of 1-Hz rTMS on separate days, one targeting right S2 and the other targeting the vertex (control). Before and after rTMS, subjects rated the intensity and pleasantness of slow and fast gentle brushing of the hand and performed a 2-point tactile discrimination task, followed by fMRI during additional brushing. rTMS to S2 (but not vertex) decreased intensity ratings of fast brushing, without altering touch pleasantness or spatial discrimination. MRI showed a reduced response to brushing in S2 (but not in S1 or insula) after S2 rTMS. Together, our results show that reducing touch-evoked activity in S2 decreases perceived touch intensity, suggesting a causal role of S2 in touch intensity perception