VIBRATION-INDUCED PRESYNAPTIC INHIBITION OF THE SOLEUS-H REFLEX IS TEMPORARILY REDUCED BY CORTICAL MAGNETIC STIMULATION IN HUMAN-SUBJECTS

We have examined the effects of a transcranial magnetic stimulus (TMS) on the H reflex of the soleus muscle during vibration-induced presyna ptic inhibition of the reflex, in seven normal volunteers. Without vib ration, the H reflex was facilitated at interstimulus time intervals o f greater than or equal to 5 ms after TMS. With vibration, the H refle x was markedly reduced or completely inhibited in control trials, but facilitation by TMS was noticed at intervals as short as -2.5 ms. Thes e findings indicate an effect of TMS on the spinal interneurons mediat ing presynaptic vibratory inhibition of the H reflex.