Influence of vibratory stimuli induced by transcranial stimulation on motor evoked potentials of masseter muscles

Abstract

We investigated the influence of vibratory stimuli on motor evoked potentials (MEPs) in masseter muscles using transcranial magnetic stimulation. A double cone coil driven by a Magstim Model 200 magnetic stimulator was placed on the skull overlaying the right temporal area. The stimulus intensity was set to 50% of maximum output. As a control, we measured the MEP at 50% of maximum clenching before vibratory stimuli. We instructed five volunteers to clench at 50% maximum contraction every 15 seconds for 2 minutes after application of 120Hz vibratory stimuli to the mentalis for 20 seconds. Magnetic stimulation was applied during clenching. Latency and amplitude were measured for the MEP on the ipsilateral side (R-MEP) and contralateral side (C-MEP). We found that the latency of both MEPs remained unchanged after application of vibratory stimuli. The amplitude of R-MEPs decreased compared with the controls, while C-MEPs increased. A significant difference was observed between the R-MEPs and C-MEPs. These findings indicate that vibratory stimuli enhance excitability in the motor cortex.