Effects of Transcranial Magnetic Stimulation (TMS) on Somatosensory Perception

National Center For Complementary & Integrative Health

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Abstract

This study tests the general hypothesis that activation of primary somatosensory cortex (S1) is necessary for discriminative aspects of tactile perception (where and when touch occurs), but is not necessary for affective appreciation of touch (the feeling of pleasantness/unpleasantness of touch). We are using low frequency repetitive transcranial magnetic stimulation (rTMS) to temporarily reduce activity in the right hemisphere S1 of adult human volunteers. We then conduct sensory testing to examine the influence of this deactivation on spatial tactile discrimination and on the perceived intensity and affective valence (pleasantness) of gentle touch (using a soft brush). Healthy adult volunteers are recruited and pre-screened by telephone and a screening visit is conducted to determine eligibility. Eligible participants participate in a 2-hour MRI and questionnaire session and two 1.5-hour rTMS and psychophysical testing sessions. In Session 1, a structural magnetic resonance imaging (MRI) and a functional magnetic resonance imaging (fMRI) scan are collected during hand movement and touch to assist with localization of the hand area for TMS and also to compare how the brain processes slow and fast touch on the palm versus back of the hand. In addition, participants complete several questionnaires about touch and personality traits. In Sessions 2 and 3, rTMS is performed over S1 in an attempt to interfere with sensory brain activity (active condition) or over the vertex (top of the head; control condition) while tactile stimuli are presented and rated by the participant. If our hypothesis is correct, rTMS over S1, but not over the vertex, will alter sensory discrimination but will NOT alter affective ratings of touch. This protocol was written in October of 2013 and submitted in November 2013. It was approved in March of 2014. We have completed about two-thirds of data collection including MRI scans, rTMS sessions, and behavioral testing. Behavioral ratings collected thus far show the expected pattern of preference for slow touch (versus fast touch) on the back of the hand.