Attenuation of somatosensory evoked potentials by acupuncture and tactile skin stimulation in man.

The effects of acupuncture and tactile skin stimulation on somatosensory evoked potentials (SEPs), elicited by the median nerve stimulation, were investigated in healthy subjects. Acupuncture needles were inserted into either Hegu plus Shousanli, Hegu plus Waiguan, or Shousanli positions ipsilateral to the median nerve stimulation. Tactile skin stimulation was applied to either the ulnar side of the palm, or the dorsal surface of the hand or forearm ipsilaterally to the nerve stimulation. It was found that acupuncture significantly suppressed the amplitude of P22 and P40, and that the tactile skin stimulation of the ulnar side of the palm significantly suppressed the amplitude of P22 and P40, but that the peak latencies were not affected. Dipole tracing analysis showed that the location and vector direction of P22 were not changed but the vector moment of P22 was changed by both acupuncture and tactile stimulation. Based on these findings the suppressive effect of acupuncture and skin stimulation on P22 was proposed to be due to the afferent inhibition in the somatosensory cortex. Although the suppressive mechanism of P40 by tactile skin stimulation seemed to be similar to that of P22, the suppression of P40 by acupuncture appeared to include different mechanisms.