Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland.
Brain Stimul. 2012 Oct;5(4):526-32. doi: 10.1016/j.brs.2011.07.006. Epub 2011 Aug 9.
To determine whether a second-scale intertrial interval (ITI) of single-pulse transcranial magnetic stimulation (TMS) affects the measured amplitude of motor-evoked potentials (MEPs) representing individual corticospinal excitability. This was performed to challenge the common assumption of time invariance of such amplitudes.
Navigated TMS was used to map the dominant hemisphere of nine healthy subjects for the cortical representation focus of the contralateral thenar muscle, and resting motor threshold (MT) was determined. Single-trial MEP amplitudes were analyzed from trains of 30 responses induced at an intensity of 120% of the MT, and constant ITIs were investigated at 1, 2, 3, 5, and 10 seconds as well as randomized at ranges of 1-3 seconds, 3-5 seconds, and 5-10 seconds. MEP responses were divided into three blocks of 10 consecutive responses within each stimulation train. Repeated samples ANOVA was used to assess whether the individual characteristic MEP amplitudes were time invariant, i.e., not affected by the different ITIs and stimulus blocks.
The individual single-trial MEP amplitudes were affected significantly (P < 0.05) by the ITI (8/8 subjects), block number (5/8 subjects), and ITI by block number interaction (6/8 subjects). One subject was excluded as the sphericity of the variances could not be confirmed. Consequently, the found time variant nature of the individual single-trial MEP amplitudes affected the estimates (means) of individual characteristic MEP amplitudes. This was also observed as a significant block number effect (P < 0.05) across all subjects.
The individual characteristic MEP amplitudes are time variant, contrary to the common assumption. Hence, individual characteristic MEP amplitude estimates should be used cautiously, as erroneous conclusions could be made when assuming those as time invariant.
确定单脉冲经颅磁刺激（TMS）的第二个间隔时间（ITI）是否会影响代表个体皮质脊髓兴奋性的运动诱发电位（MEP）的测量幅度。这是为了挑战这些幅度时间不变性的常见假设。
使用导航 TMS 对 9 名健康受试者的优势半球进行了对侧鱼际肌的皮质代表区域映射，并确定了静息运动阈值（MT）。从强度为 MT 的 120%的 30 次反应引发的刺激序列中分析了单试 MEPs 幅度，研究了 1、2、3、5 和 10 秒的恒定 ITI 以及在 1-3 秒、3-5 秒和 5-10 秒范围内随机的 ITI。MEP 反应在每个刺激序列的 10 个连续反应中分为三个块。使用重复样本方差分析评估个体特征 MEPs 幅度是否时间不变，即不受不同 ITI 和刺激块的影响。
个体单试 MEP 幅度受 ITI（8/8 个受试者）、块数（5/8 个受试者）和 ITI 与块数交互作用（6/8 个受试者）的显著影响（P < 0.05）。由于不能确认方差的球形性，有 1 个受试者被排除在外。因此，个体单试 MEP 幅度的时间变化性质会影响个体特征 MEP 幅度的估计值（平均值）。这也被观察到在所有受试者中都存在显著的块数效应（P < 0.05）。
个体特征 MEP 幅度是时间变化的，与常见假设相反。因此，当假设这些幅度是时间不变时，应谨慎使用个体特征 MEP 幅度估计值，因为可能会得出错误的结论。
