High rates of variability in the amplitude of transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs), a popular method for assessing corticospinal excitability (CSE), make it essential to examine inherent reliability of the MEP amplitude. We aimed to investigate the effects of different intertrial intervals (ITIs) of single-pulse TMS on the amplitude, variability, and test-retest reliability of MEPs. Twenty-five TMS single pulses were recorded at four different ITIs of 5, 10, 15, and 20 sec from 15 healthy participants who attended two experimental sessions. Repeated measures analysis of variance (rmANOVA) and standardized z-value standard deviations (SDs) were used to investigate the effects of ITIs on MEP amplitudes and variability. Test-retest reliability of MEP amplitudes was also assessed using rmANOVA and intraclass correlation (ICC). rmANOVA revealed significantly larger MEP amplitudes following ITIs of 10, 15, and 20 sec compared with ITI 5, with no significant increases between ITIs of 15 and 20 sec. Standardized z-value SDs revealed variability rate reduction following longer ITIs with significant reductions occurring following ITIs of 10, 15, and 20 sec compared with ITI 5 with no significant difference between ITIs of 15 and 20 sec. rmANOVA showed no significant Time main effect on the MEP changes confirming within- and between-session agreement. ICCs reported significant within- and between-session reliability in all selected ITIs. The findings of the current study indicate that longer ITIs up to 15 sec can significantly induce larger MEPs with lower variability and higher reliability. The increase in ITIs not only reduces the chance of TMS-induced changes in CSE but also helps us to use this assessment tool in studies with smaller sample sizes.

中文翻译：

---

较长的经颅磁刺激间隔增加了尺寸，降低了变异性，并提高了电机诱发电位的可靠性。

经颅磁刺激（TMS）诱发的运动诱发电位（MEPs）幅度的高变化率是评估皮质脊髓兴奋性（CSE）的一种流行方法，因此必须检查MEP幅度的固有可靠性。我们旨在研究单脉冲TMS的不同心律间隔（ITI）对MEP的幅度，变异性和重测可靠性的影响。在参加两次实验的15位健康参与者中，分别在5、10、15和20秒的四个不同的ITI上记录了25个TMS单脉冲。重复测量方差分析（rmANOVA）和标准化z值标准差（SDs）用于研究ITI对MEP振幅和变异性的影响。还使用rmANOVA和类内相关性（ICC）评估了MEP幅度的重测信度。rmANOVA显示，与ITI 5相比，ITI在10、15和20秒后的MEP幅度明显更大，而ITI在15和20秒之间没有显着增加。标准化的z值SD显示，与ITI 5相比，较长的ITI与10、15和20秒的ITI相比，可变性降低，而ITI在5、15和20秒之间无显着差异。rmANOVA显示对MEP更改没有明显的时间主效应，证实了会话内和会话间协议。ICC报告在所有选定的ITI中，会话间和会话间的可靠性都很高。当前研究的结果表明，长达15秒的更长的ITI可以以较低的变异性和较高的可靠性显着诱导较大的MEP。ITI的增加不仅减少了TMS引起的CSE变化的机会，而且还帮助我们在样本量较小的研究中使用此评估工具。