Accelerometry as a tool for measuring the effects of transcranial magnetic stimulation
Gautier Hamoline1, Elise E Van Caenegem1, Baptiste M Waltzing1
1Institute of Neurosciences, UC Louvain, Avenue Mounier 54, Bruxelles 1200, Belgium.
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 (χ2(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.
