[Somatosensory evoked potentials: interference and perceptual masking of cutaneous afferents in man]

Somatosensory evoked potentials (SEP) are attenuated following double electrical stimulation of the fingers (II + III). This effect is observed at cervical (N13), parietal (N20-P27) and frontal (P22-N30) levels. We simultaneously observed in the same subjects that cutaneous perception of the test-shock is completely suppressed with interstimulus intervals (ISI) within a 0-10 msec range. With 25-30 msec ISI, the perceptive function totally recovers, but SEP inhibition remains at 50 % of the control. The SEP reduction does not result in a perception deficit as long as the cortical-test response exceeds 50% of control. These results suggest that: SEP inhibition could be a local but durable phenomenon occurring at both cervical and cortical levels. Cutaneous perception does not necessitate a maximal SEP development. The perceptive process involves other associative areas (5,7...) and is activated when the primary cortical activation exceeds a certain threshold which was found at 50% of the unconditioned response voltage.