Neural substrates in secondary somatosensory area for the perception of different tactile sensations

This functional magnetic resonance imaging (fMRI) study investigated the secondary somatosensory area (SII) in humans, especially regarding the presence of distinctive spatial arrangements of neural subunits responding to different types of tactile stimuli. Ten healthy volunteers received four different sensory stimuli on the palmar side of the right hand - vibrotactile, pressure, warmth, and coolness. Based on group-level analysis of the fMRI data, all four of the somatosensory stimuli resulted in activations in the bilateral SII and insula as well as the SI contralateral to the stimulation. The spatial distribution of neural activations corresponding to each stimulus, as examined by cortical inflation technique, revealed significant overlaps, but also showed the differences in terms of its overall topology. The local maxima of the activation within the SII, corresponding to these stimuli, manifested distinctive spatial location. These results suggest that differential networks of the SII subregions are involved in the processing of the different nature of the tactile stimuli, while sharing common regions in the parietal operculum.