Primary somatosensory cortex discriminates affective significance in social touch

Being caressed by another person is one of the most powerfully emotional of social signals. Current views about tactile processing propose a strict dichotomy: one stream, involving the insula, processes affective qualities, while another, involving primary somatosensory cortex (SI), processes sensory properties. We argue against this dichotomy by showing that SI encodes affective information about a sensual caress, and can do so from visual information alone. We applied multivariate pattern classification to fMRI data from a study in which heterosexual males believed they were sensually caressed by a man or woman, while the caress was always given by the same woman. This design allowed us to selectively manipulate the affective quality of the caress. We found that SI encoded the affective quality during the caress just as well as the insula, forcing a revision of current processing schemes and demonstrating a novel function for primary somatosensory cortex in affective touch.