5 Hz Repetitive Transcranial Magnetic Stimulation with Maximum Voluntary Muscle Contraction Facilitates Cerebral Cortex Excitability of Normal Subjects

Background: Recently, high-frequency repetitive transcranial magnetic stimulation (rTMS) is reported to evaluating the corticospinal pathway and improving both cortical excitability and motor function significantly in subjects. According to some previous reports, the maximum voluntary muscle contraction (MVC) of target muscle can reinforce the influence by rTMS. The aim of this study was to confirm 5 Hz rTMS with MVC in healthy individuals is an effective method to facilitate motor neuron excitability and the efficiency can last at least 30min post stimulation. Objective: To compare the motor evoked potentials (MEPs) elicited by 5Hz rTMS and 5Hz rTMS combined with MVC. Methods: In this randomized, controlled, assessor-blinded, crossover trial, 40 healthy right-handed subjects were divided into group A (n=20) and group B (n=20). All subjects received rTMS over the primary motor cortex area (M1) in the left hemisphere. The parameters of rTMS were 5 Hz, 90of the resting motor threshold (RMT), for a total of 500 pulses in100 trains (1-sec inter-stimulus and 8- sec inter-interval). Method 1: All subjects received rTMS over the hand area of left M1. Method 2: All subjects received rTMS at the same stimulated point, combined with maximum voluntary hand griping in each 10 trains. Test 1: group A underwent method 1, while group B underwent method 2. Test 2: A week later, group B underwent method 1, while group A underwent method 2. In each test, the MEP amplitude and latency was measured before (P-rTMS), 5min after (Post 1) and 30min after (Post 2) the rTMS intervention. Results: MEP amplitude increased significantly from baseline at 5 minutes post intervention under both treatment regimes. However for both sequences, it decreased towards baseline under the rTMS intervention at 30 minutes post intervention but remained relatively high when rTMS was combined with MVC. MEP latency decreased significantly from baseline at 5 minutes post intervention under both treatment regimes. For both sequences, it then increased again towards baseline under both treatment regimes at 30 minutes post intervention. Although there was a trend for a less pronounced increase under the combined treatment, this effect was not significant. Conclusion: Both 5Hz rTMS and 5Hz rTMS combined with MVC facilitate motor cortical excitability, but the enhancement in rTMS with MVC is more pronounced and maintained longer than simple rTMS. Keywords: Repetitive transcranial magnetic stimulation; motor evoked potentials; maximum voluntary muscle contraction; primary motor cortex area.