The amplitude of motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) over the motor cortex is influenced by multiple factors. TMS delivery is accompanied by an abrupt clicking noise which can induce a startle response. This study investigated how masking/attenuating the sound produced by the TMS system discharging influences MEP amplitudes. In addition, the effects of increasing the time between consecutive stimuli and of making participants aware of the time at which they would be stimulated were studied. MEPs were recorded from the Flexor Carpi Radialis (FCR) muscle at rest by stimulation at motor threshold (MT), 120% MT and 140% MT intensity. Participants (N = 23) received stimulation under normal (NORMAL) conditions and while: wearing sound-attenuating earmuffs (EAR); listening to white noise (NOISE); the interval between stimuli were prolonged (LONG); stimulation timing was presented on a screen (READY). The results showed that masking (p = 0.020) and attenuating (p = 0.004) the incoming sound significantly reduced the amplitude of MEPs recorded across the intensities of stimulation. Increasing the interval between pulses had no effect on the recorded traces if a jitter was introduced (p = 1), but making participants aware of stimulation timing decreased MEP amplitudes (p = 0.049). These findings suggest that the sound produced by TMS at discharging increases MEP amplitudes and that MEP amplitudes are influenced by stimulus expectation. These confounding factors need to be considered when using TMS to assess corticospinal excitability.

经颅磁刺激 (TMS) 在运动皮层上引起的运动诱发电位 (MEP) 的幅度受多种因素的影响。TMS 传递伴随着突然的咔哒声，可引起惊吓反应。本研究调查了 TMS 系统放电产生的声音的掩蔽/衰减如何影响 MEP 幅度。此外，还研究了增加连续刺激之间的时间以及使参与者意识到他们将受到刺激的时间的影响。通过运动阈值 (MT)、120% MT 和 140% MT 强度的刺激，从静止的桡侧腕屈肌 (FCR) 肌肉记录 MEP。参与者 (N = 23) 在正常 (NORMAL) 条件下接受刺激，同时： 佩戴消音耳罩 (EAR)；听白噪声（NOISE）；刺激之间的间隔延长（LONG）；刺激时间显示在屏幕上（就绪）。结果表明，掩蔽（p  = 0.020）和衰减（p  = 0.004）传入的声音显着降低了在刺激强度上记录的 MEP 的幅度。如果引入抖动（ p = 1），增加脉冲之间的间隔对记录的轨迹没有影响 ，但让参与者意识到刺激时间会降低 MEP 幅度（p  = 0.049）。这些发现表明，TMS 在放电时产生的声音会增加 MEP 幅度，并且 MEP 幅度受刺激预期的影响。在使用 TMS 评估皮质脊髓兴奋性时，需要考虑这些混杂因素。