Effect of electroacupuncture and transcutaneous electrical nerve stimulation at Hegu (LI.4) acupuncture point on the cutaneous reflex

Our previous studies have shown that the cerebral cortex plays a modulator role in the physiological mechanisms of acupuncture and 2Hz electroacupuncture (EA), but either acupuncture or 2Hz EA appeared to have very little effect on spinal cord. However, 2Hz or 100Hz transcutaneous electrical nerve stimulation (TENS) applied to Hegu acupuncture point (LI.4) can increase the amplitude of the H-reflex, whereas manual acupuncture has no similar effect. Therefore, the aim of the present study was to further investigated the effect of 2Hz EA, 2Hz or 100Hz TENS on cutaneous reflex (CR). A total of 13 healthy adult volunteers were studied. CR recordings were obtained on the right first dorsal interosseous muscle by electrical stimulation of the ipsilateral index finger. 2Hz EA, 2Hz or 100Hz TENS was applied to the surface of the left LI.4, and then the changes of CR were observed. The results indicated that CR was characterized by an initial short latency excitatory wave (E1), followed by an inhibitory wave (11), then a long latency excitatory wave (E2). Both 2Hz EA and 2Hz TENS applied to the surface of the left LI.4 could prolong the latencies of 11 component of CR, whereas 100Hz TENS has no similar effect. In addition, either EA or TENS could not change the latencies of El, E2 component and the amplitudes of 11, E2 component of CR. In conclusion, 2Hz EA or 2Hz ENS applied to the LI.4 prolonged the latencies of 11 component of CR, suggesting that the action site of 2Hz EA or 2Hz TENS located in the supraspinal, possibly in the subcortical or cortical level. In addition, the electrical stimulation of higher frequency such as 100Hz TENS acting on CR caused habituation easier.