BACKGROUND 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. OBJECTIVE 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. METHODS 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. RESULTS 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. CONCLUSIONS 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.

中文翻译：

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刺激前皮层脑电图振荡可以预测初级运动皮层的兴奋性

背景技术单脉冲经颅磁刺激（TMS）引起的运动诱发电位（MEP）在静止状态下变化很大，但这种振幅变化的潜在机制在很大程度上是未知的。我们假设刺激前 EEG 振荡以状态相关的方式调节随后的 MEP。目标我们研究了睁眼 (EO)/闭眼 (EC) 条件下预刺激 alpha/beta 振荡与 MEP 之间的关系，然后在 EO 条件下调制 TMS 强度。此外，我们开发了一个 EEG 触发的 TMS 系统（“知情开环”）来验证我们的假设。方法 TMS 应用于左侧运动皮层。我们首先比较了使用高 TMS 强度时 EO 和 EC 条件下高振幅和低振幅 MEP 时期之间的 EEG 功率差异。下一个，我们评估了不同 TMS 强度（高与低）对 EEG-MEP 关系的影响。最后，我们使用 EEG 触发的 TMS 来确定刺激前 EEG 振荡是否预测 MEP 幅度。结果 Prestimulus 高功率 alpha/low-beta 波段仅在高强度 EO 条件下产生更大的 MEP。在 C3 和左额电极处观察到 EEG 功率和 MEP 幅度之间的正相关关系。当使用较低的 TMS 强度时，这种关系变得模糊，但在 C3 电极的高强度条件下观察到。EEG 触发的 TMS 表明，较高的 alpha 功率预测较高的 MEP 振幅，但 20 Hz 左右的 beta 功率则没有。结论 阿尔法/低贝塔振荡与静息时 MEP 振幅之间的因果关系需要在睁眼时提供高 TMS 强度。