Abstract

Objective: We predicted that accelerometry would be a viable alternative to electromyography (EMG) for assessing fundamental Transcranial Magnetic Stimulation (TMS) measurements (e.g. Resting Motor Threshold (RMT), recruitment curves, latencies). New Method: 21 participants were tested. TMS evoked responses were recorded with EMG on the First Dorsal Interosseus muscle and an accelerometer on the index fingertip. TMS was used to determine the (EMG-defined) RMT, then delivered at a range of intensities allowing determination of both the accelerometry-defined RMT and measurement of recruitment curves. Results: RMT assessed by EMG was significantly lower than for accelerometry (t(19)=-3.84, p<.001, mean +/- SD EMG = 41.1 +/- 5.28% MSO (maximum stimulator output), Jerk = 44.55 +/- 5.82% MSO), though RMTs calculated for each technique were highly correlated (r(18)=.72, p<.001). EMG/Accelerometery recruitment curves were strongly correlated (r(14)=.98, p<.001), and Bayesian model comparison indicated they were equivalent (BF01>9). Latencies measured with EMG were lower and more consistent than those identified using accelerometry (chi(2)(1)=80.38, p<.001, mean +/- SD EMG=27.01 +/- 4.58 ms, Jerk=48.4 +/- 15.33 ms). Comparison with existing methods: EMG is used as standard by research groups that study motor control and neurophysiology, but accelerometry has not yet been considered as a potential tool to assess measurements such as the overall magnitude and latency of the evoked response. Conclusions: While EMG provides more sensitive and reliable measurements of RMT and latency, accelerometry provides a reliable alternative to measure of the overall magnitude of TMS evoked responses.

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