Effects of a selective A beta afferent block on the pain-related SEP scalp topography.

This study examined the effects of a selective ischemic block of the A beta peripheral afferents on the pain-related somatosensory evoked potential (SEP). Pain descriptions given during the A beta block suggest that the SEP elicited by noxious sural nerve stimulation arises from activity in the A delta and not the C peripheral afferents. The SEP recorded during the A beta block was characterized by a potential whose latency and topographic pattern was very similar to a late pain-related positive potential (SP6) that we have described in previous work. These results provide further evidence for SP6 being generated by brain areas (sources) that receive noxious inputs and make it very unlikely that sources involved exclusively in innocuous somatosensory processes contribute to SP6.