Assessment of Motor Evoked Potential Reliability in Measuring Motor Adaptation in Lower Extremity Muscles

Transcranial magnetic stimulation (TMS) is a safe, noninvasive method used over the motor cortex to probe the electrical state of descending motor pathways by eliciting motor evoked potentials (MEPs) in targeted muscles. Characteristics of MEPs, such as magnitude and latency, reflect the underlying physiological state of the pathways being stimulated. Although numerous previous studies have examined MEP reliability in upper extremity muscles, less has been reported about the reliability of this measurement in lower extremity muscles. Thus, the current study aimed to assess the test-retest reliability of MEPs in multiple muscles of the lower extremity from a single TMS location to determine the intrinsic inter-session variability of this measurement. During three sessions separated by at least one week, electromyography (EMG) signals were recorded from the right and left tibialis anterior, soleus, rectus femoris, and biceps femoris muscles at two stimulation intensities (110% and 120% resting motor threshold). MEP size was quantified using integrated magnitude and peak-to-peak amplitude of the MEP waveform. A linear mixed effects model was fitted with within-participant slope and intercepts, and overall slope and intercept fixed effects of session, resting motor threshold, and coil accuracy. Preliminary results suggest that MEP size may differ across sessions; therefore, discussion will focus on inter-session reliability quantified using intraclass correlation coefficients (ICC) and the Bland-Altman analysis. Results of the current study will inform the ongoing assessment of neurophysiological correlates underlying longitudinal treadmill training for physical rehabilitation at the National Center for Adaptive Neurotechnologies in Albany, New York.