Intra-rater within- and between-session reliability of TMS-induced MEPs: peak-to-peak amplitude versus area under the curve

Corticospinal excitability (CSE) is the responsiveness of the corticospinal and brain-to-muscle pathway, assessed using motor-evoked potentials (MEPs) via transcranial magnetic stimulation (TMS). It provides crucial insight into motor control, neuroplasticity, and neurological conditions. The use of TMS-induced MEPs in clinical and research contexts is contingent upon their intra- and intersession reliability. This study specifically aimed to assess the reliability of two distinct methods for quantifying MEP size: peak-to-peak amplitude (PPA) and the area under the curve (AUC). Establishing the agreement between these quantification methods is critical for ensuring consistent measurements by the same assessor, especially in pre- and post-test designs conducted within and between sessions. Twelve healthy participants volunteered for this study. Thirty MEPs were recorded from each participant using a single-pulse TMS set at 120% of the resting motor threshold (RMT) over two sessions. The first session consisted of two tests (T1 and T2) with a 20-minute rest interval between sets. The second session included one set of tests (T3). Test-retest reliability of MEP amplitude and AUC were assessed using one-way ANOVA and Intraclass Correlation Coefficient (ICC). A one-way ANOVA revealed no significant effect of time on MEP amplitude or AUC value, indicating agreement between sessions. The ICC demonstrated significant intra- and inter-session reliability for PPA. However, correlations between T1-T3 were weak for AUC values. In conclusion, this study suggests that PPA a more reliable measurement than AUC for assessing changes in CSE. Future investigations should explore the reliability of the AUC method in clinical settings or research protocols.