Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-Ku, Fukuoka, 812-8582, Japan.
Department of Clinical Neurophysiology, Neurological Institute, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-Ku, Fukuoka, 812-8582, Japan.
Brain Stimul. 2019 Nov-Dec;12(6):1508-1516. doi: 10.1016/j.brs.2019.06.013. Epub 2019 Jun 12.
The motor evoked potentials (MEPs) elicited by single-pulse transcranial magnetic stimulation (TMS) vary considerably at rest, but the mechanism underlying this amplitude variation is largely unknown. We hypothesized that prestimulus EEG oscillations modulate the subsequent MEPs in a state-dependent manner.
We studied the relationship between prestimulus alpha/beta oscillations and MEPs during eyes open (EO)/closed (EC) conditions, and then modulated TMS intensity in the EO condition. Furthermore, we developed an EEG-triggered TMS system ("informed open-loop") to verify our hypothesis.
TMS was applied to the left motor cortex. We first compared EEG power differences between high- and low-amplitude MEP epochs in the EO and EC conditions when using a high TMS intensity. Next, we evaluated the effects of varying TMS intensities (high vs. low) on the EEG-MEP relationship. Finally, we used EEG-triggered TMS to determine whether prestimulus EEG oscillations predicted MEP amplitudes.
Prestimulus higher-power alpha/low-beta bands produced larger MEPs only in the high-intensity EO condition. A positive relationship between EEG power and MEP amplitude was observed at C3 and left frontal electrodes. This relationship was obscured when using the lower TMS intensity but was observed in the high-intensity condition at the C3 electrode. EEG-triggered TMS demonstrated that higher alpha power predicted higher MEP amplitudes, but beta power at around 20 Hz did not.
A causal relationship between alpha/low-beta oscillations and MEP amplitudes at rest requires high TMS intensity delivered when eyes are open. This association may allow us to develop a new informed open-loop TMS protocol.
单脉冲经颅磁刺激（TMS）诱发的运动诱发电位（MEPs）在静息时变化很大，但振幅变化的机制在很大程度上尚不清楚。我们假设刺激前的脑电图（EEG）振荡以状态依赖的方式调节随后的 MEPs。
我们研究了睁眼（EO）/闭眼（EC）状态下刺激前 alpha/beta 振荡与 MEPs 之间的关系，然后调节了 EO 状态下的 TMS 强度。此外，我们开发了一种 EEG 触发的 TMS 系统（“知情开环”）来验证我们的假设。
TMS 施加于左侧运动皮层。我们首先比较了在使用高 TMS 强度时 EO 和 EC 条件下高、低振幅 MEP 时程之间的 EEG 功率差异。接下来，我们评估了改变 TMS 强度（高与低）对 EEG-MEP 关系的影响。最后，我们使用 EEG 触发 TMS 来确定刺激前的 EEG 振荡是否可以预测 MEPs 的振幅。
刺激前较高的 alpha/较低的 beta 频段功率仅在高 TMS 强度的 EO 条件下产生更大的 MEPs。在 C3 和左额电极处观察到 EEG 功率与 MEP 振幅之间存在正相关关系。当使用较低的 TMS 强度时，这种关系变得模糊，但在 C3 电极的高 TMS 强度条件下可以观察到。EEG 触发的 TMS 表明，较高的 alpha 功率预测更高的 MEP 振幅，但约 20 Hz 的 beta 功率则没有。
当眼睛睁开时，高 TMS 强度诱发的 alpha/low-beta 振荡与静息时的 MEP 振幅之间存在因果关系。这种关联可能使我们能够开发一种新的知情开环 TMS 协议。
