Abstract
Using somatosensory evoked potentials (SEP), we investigated the effects of auditory stimulation and exercise on the human somatosensory area. SEP elicited by the right median nerve stimulation at the wrist of 19 healthy volunteers was recorded from Fpz and P3'. Then the amplitude and latency of N20 and P25 included in the early components of SEP were investigated. In the first experiment, we observed the relationship between sound pressure level and SEP. The sound was composed of nine train pulses with 0.1ms durations. Between the onset of each pulse was 6ms. The sound pressure level ranged from 50 to 100dB (SPL). Auditory stimulation was presented to both ears using headphones. In the second experiment, the effects of auditory stimulation on the early components of median nerve stimulation were examined during 10% maximal voluntary contractions of thenar eminence, and right median nerve stimulation at the wrist was given after auditory stimulation. The interval between auditory stimulation and median nerve stimulation ranged from 0-50ms in 10ms increments. These interstimulus intervals were randomly intermixed with control trials which were without auditory stimulation. Auditory stimulation, which was 50dB higher than the auditory threshold, suppressed the amplitude of N20. During exercise, auditory stimulation strongly suppressed the amplitude of N20 when it preceded the electric stimulation to the median nerve at 20ms. These results show that auditory stimulation that is 50dB higher than the auditory threshold inhibit somatosensory activity. Furthermore, inhibitory action on the somatosensory area by auditory stimulation seems to be associated with gating phenomenon.
