Effects of visual and auditory stimuli on median nerve somatosensory evoked potentials in man

To demonstrate electrophysiological evidence of neural connections of somatosensory with visual and auditory pathways, interactions of median nerve somatosensory evoked potentials (SEPs) with visual evoked potentials (VEPs) and auditory evoked potentials (AEPs) were analyzed in 12 healthy subjects. In Experiment I (SEP vs. VEP), three patterns of stimulation, namely, electric stimulation of left median nerve, binocular LED flash, and simultaneous electric and flash stimulation, were applied with random interstimulus intervals of 2-4 sec until more than 100 responses had been obtained and averaged for each pattern of stimulation. Simultaneous electric and visual responses were subtracted from arithmetical sums of SEPs and VEPs to show interactions between somatosensory and visual responses. In Experiment II (SEP vs. AEP), binaural short-duration tone bursis instead of LED flashes were used in the same manner as in Experiment I, and interactions between somatosensory and auditory responses were analyzed. Results indicated that the effects of both visual and auditory interaction on SEPs were significant around 120-130 msec of latency. In other words, cross-modal sensory interaction occurred in the late phase of sensory processing.