SOMATOSENSORY-EVOKED POTENTIALS - INTERFE RENCES AND PERCEPTIVE MASKING OF CUTANEOUS AFFERENTS IN MAN

Somatosensory evoked potentials (SEP) are attenuated following double electrical stimulation of the fingers (II + III). This effect is obser ved at cervical (N13), parietal (N20-P27) and frontal (P22-N30) levels . We simultaneously observed in the same subjects that cutaneous perce ption of the test-shock is completely suppressed with interstimulus in tervals (ISI) within a 0-10 msec range. With 25-30 msec ISI, the perce ptive 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 r esults suggest that: SEP inhibition could be a local but durable pheno menon occurring at both cervical and cortical levels. Cutaneous percep tion does not necessitate a maximal SEP development. The perceptive pr ocess 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.