Differential organization of touch and pain in human primary somatosensorycortex

Processing of tactile stimuli within somatosensory cortices has been shown to be complex and hierarchically organized. However, the precise organizati on of nociceptive processing within these cortices has remained largely unk nown. We used whole-head magnetoencephalography to directly compare cortica l responses to stimulation of tactile and nociceptive afferents of the dors um of the hand in humans. Within the primary somatosensory cortex (SI), noc iceptive stimuli activated a single source whereas tactile stimuli activate d two sequentially peaking sources. Along the postcentral gyrus, the nocice ptive SI source was located 10 mm more medially than the early tactile SI r esponse arising from cytoarchitectonical area 3b and corresponded spatially to the later tactile SI response. Considering a mediolateral location diff erence between the hand representations of cytoarchitectonical areas 3b and 1, the present results suggest generation of the single nociceptive respon se in area I, whereas tactile stimuli activate sequentially peaking sources in areas 3b and 1. Thus nociceptive processing apparently does not share t he complex and hierarchical organization of tactile processing subserving e laborated sensory capacities. This difference in the organization of both m odalities may reflect that pain perception rather requires reactions to and avoidance of harmful stimuli than sophisticated sensory capacities.