Effective Intervention Methods to Improve Spinal Reciprocal Inhibition

Abstract

Spinal reciprocal inhibition (RI) is an important mechanism to carry out smooth joint movements and optimize gait. This mechanism includes disynaptic RI and presynaptic inhibitions. In disynaptic RI, direct synaptic coupling from primary afferent (Ia) fibers in the main operating muscle inhibits the spinal anterior horn cells of the antagonist muscle via Ia inhibitory interneurons. In presynaptic inhibitions, afferent Ia fibers in the main operating muscle bind to the terminals of afferent Ia fibers in the antagonist muscle via depolarization of primary afferent interneurons. Through these inhibitory pathways, RI works to inhibit excessive muscle contraction in the antagonist muscle, thereby enabling coordinated movement. Upper motor neuron disorders and aging cause functional decline of the RI. In recent years, the RI enhancement method has attracted attention because the decrease in RI function causes excessive co-contraction. Brain stimulation and peripheral stimulation are effective interventions for RI enhancement. Therefore, we focused on stimulating the supplementary motor area in the brain and on repetitive passive movement in our experiments. In each stimulation method, RI potentiation was observed at a shorter intervention time than in previous studies, and the after-effect was sustained. We believe that these interventions are simple and inexpensive, can decrease excessive co-contraction, have a high spillover effect, and can be applied in rehabilitation.