Modulation of H Reflex and Reciprocal Inhibition of Soleus Muscle via Electrical and Transcranial Magnetic Stimulation of Antagonist Muscle

ABSTRACT

OBJECTIVE: To evaluate the effect of a transcranial magnetic stimulation on reciprocal inhibition of the human leg. METHOD: Twenty healthy human subjects who showed significant inhibition of soleus H reflex after conditioning electrical stimulation of tibialis anterior at a conditioning-test interval of 2 ms were included in this study. Changes in the amount of reciprocal inhibition by conditioning electrical stimulus were compared after transcranial magnetic stimulation of tibialis anterior. RESULTS: Approximately 12% inhibition of H reflex was produced by motor threshold stimulation, and 14% inhibition by maximum stimulation of common peroneal nerve. When a submotor threshold cortical shock was given with test-conditioning interval 0 ms, this inhibition was not significantly changed. There was no significant change of H reflex amplitude ratio by conditioning electrical stimulation after delivering supramotor threshold cortical shock. Amplitude of H reflex was enhanced by transcranial magnetic stimulation at each same conditioning electrical stimulation. CONCLUSION: We conclude that TMS can produce excitatory effects on spinal motor neurons rather than Ia inhibitory interneuron and there is no evidence for convergence onto Ia inhibitory interneurons from the fiber systems excited by magnetic stimulation over the cortex.