[Somatosensory evoked potential and pain. I. Late cortical responses obtained at different levels of stimulation].

The characteristics of the late components of the somatosensory evoked potential (SEP) as a function of stimulation intensity have been studied in 10 normal volunteers following electrical stimulation of the distal cutaneous branches of the median nerve. The stimulus intensity (either single shock or train) was adapted in order to produce the following 4 types of sensation: liminal tactile (ST); frankly tactile but never painful (4 times ST); pain threshold (SD); and 1.5 time SD. A significant relationship was observed between the amplitude of the late component (N150-P220-N400), of the SEP and the stimulus intensity for a low rate of stimulation (below 0.25 Hz). In contrast this relationship is not verified for higher stimulation rates. These data are discussed with respect to their implication in pain research.