Somatosensory stimulation (acupuncture) modulates spinal and supraspinal motor neuron excitability.

Abstract

It has been reported that acupuncture is effective in alleviating abnormalities of muscle tone caused by abnormal motor neuron excitability such as spastic paralysis caused by cerebrovascular disorder. However, the underlying mechanism is unclear. Thus, we examined the effect of acupuncture stimulation on long-latency reflexes (LLR) to determine the site of action of acupuncture stimulation in modulating motor reflexes. The amplitude ratio of LLR/M was reduced by the acupuncture stimulation of LI4 (hand). Furthermore, we examined the effect of acupuncture stimulation on blink reflexes. The R2 component of blink reflexes was decreased by the acupuncture stimulation of LI4 (hand). LLR is the motor reflex of the central nervous system via such as cerebral cortex of supraspinal pathways. In addition, blink reflexes are the motor reflex of the central nervous system via such as brain stem. These findings suggest that acupuncture stimulation inhibits motor nerve reflexes via supraspinal modulation systems. Furthermore, we examined the effect of acupuncture stimulation on electromyogram F-wave to determine the effect of acupuncture stimulation on the excitability of spinal motor neurons. The result of this study indicated that acupuncture stimulation may have a greater effect on the excitability of spinal motor neurons.