Effect of body positions on outcomes of single-pulse transcranial magnetic stimulation

Abstract Background Transcranial magnetic stimulation (TMS) elicits motor evoked potentials (MEPs) and assesses motor cortex and corticospinal tract physiology. Various factors influence MEPs. This study aimed to compare TMS findings between sitting and supine positions. Methods Single-pulse TMS was applied to 20 healthy individuals (12 males, 8 females) in both sitting and supine positions using a round coil. MEPs were recorded from the abductor digiti quinti and tibialis anterior muscles. Resting motor threshold (RMT), active motor threshold (AMT), MEP amplitude and latency, central motor conduction time (CMCT), and cortical silent period (CSP) were compared between the two positions. Results The mean RMT/AMT for the right upper extremity were 44.10 ± 9.00%/34.90 ± 7.09% in the sitting position and 50.09 ± 8.76%/39.70 ± 7.81% in the supine position, respectively ( p < 0.001 for RMT, p = 0.003 for AMT). For the right lower extremity, the mean RMT/AMT were 61.55 ± 10.77%/45.00 ± 10.72% in the sitting position and 68.70 ± 10.55%/52.75 ± 9.89% in the supine position, respectively ( p < 0.001 for RMT and AMT). MEP latency and amplitude, CMCT, and CSP did not show any significant differences between positions. Conclusions The sitting position may be preferable for routine TMS, as lower motor thresholds allow the use of lower stimulation intensities and may improve tolerability. However, as MEP findings were similar between the two positions, TMS can be applied in the supine position for patients at risk of seizures or syncope to prevent syncope or seizure-related complications.