Cortical component of the somatosensory evoked potential elicited by median nerve stimulation was attenuated by passive, active movement of ipsilateral hand and tactile, vibratory stimulation of hand.

This study was carried out to investigate the effect of a variety of "interfering" stimuli on the median derived somatosensory evoked potentials and its mechanial interaction. The interfering stimuli were passive, active movement and tactile, vibratory stimuli on ipsilateral hand and the potentials were recorded over Erb's point, cervical spine and scalp.

The results are as follows:

1) The latencies of Erb's, cervical and cortical potentials were 9.15±0.41, 12.60±9.79, 18.25±0.77 msec, respectively in Baseline recording and the differences of latencies with interfering sensory stimuli were not statistically significant (p>0.05).

2) The amplitudes of Erb's, cervical potentials were 3.91±1.39, 4.15±1.04uV, respectvely in baseline recording and the differences of amplitudes with interfering sensory stimuli were not statistically significant (p>0.05).

3) The amplitude of cortical potential were 4.76±1.86 uV in baseline recording and the mean percentages of amplitude reduction were 37.29±13.34% (3.01±1.36 uV) by vibratory stimuli, 26.94±10.21% (3.45±1.39 uV) by active movement, 19.47±10.40% (3.83±1.58 uV) by passive movement and 12.05±10.91% (4.19±1.73 uV) by tactile stimulation. These were statistically significant (p<0.001).

4) The amplitude reduction of cortical potential is related to the central interaction, not to the peripheral interaction.