NIH Research Festival
Several lines of evidence suggest a separation of somatosensory processing in the cortex, with primary somatosensory (S1) cortex critical for discriminative touch, and other regions necessary for emotional aspects of somatosensation. Nevertheless, some evidence contradicts this dichotomy. Here we used low frequency repetitive transcranial magnetic stimulation (rTMS) to temporarily deactivate S1 cortex and directly test the effect of this deactivation on discriminative and affective aspects of touch. We applied 20 minutes of inhibitory 1-Hz rTMS over right hemisphere S1 or over the vertex (control location) in healthy adult subjects. Sensory testing before and after each rTMS session revealed differences in discriminative touch: two-point discrimination performance was poorer after S1 rTMS than after vertex rTMS. After S1 rTMS- but not after vertex rTMS- subjects with reduced sensory discrimination also rated touch as more intense. rTMS did not alter ratings of touch pleasantness. In addition, using fMRI to examine S1 activation during fast and slow brushing of the hand, we found that ratings of intensity- but not of pleasantness- were a significant within-subject predictor of S1 activation. Together, these findings provide the most direct evidence to date that S1 preferentially mediates discriminative rather than affective aspects of touch perception.
Scientific Focus Area: Institute, Center, and Scientific Directors
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