Defitech Chair of Clinical Neuroengineering, Neuro-X Institute (INX), Ecole Polytechnique Fédérale de Lausanne (EPFL), Geneva 1202, Switzerland.
Defitech Chair of Clinical Neuroengineering, Neuro-X Institute (INX), Ecole Polytechnique Fédérale de Lausanne (EPFL Valais), Sion 1951, Switzerland.
J Neural Eng. 2024 Jan 23;21(1). doi: 10.1088/1741-2552/ad1dc2.
The literature investigating the effects of alpha oscillations on corticospinal excitability is divergent. We believe inconsistency in the findings may arise, among others, from the electroencephalography (EEG) processing for brain-state determination. Here, we provide further insights in the effects of the brain-state on cortical and corticospinal excitability and quantify the impact of different EEG processing.Corticospinal excitability was measured using motor evoked potential (MEP) peak-to-peak amplitudes elicited with transcranial magnetic stimulation (TMS); cortical responses were studied through TMS-evoked potentials' TEPs features. A TMS-EEG-electromyography (EMG) dataset of 18 young healthy subjects who received 180 single-pulse (SP) and 180 paired pulses (PP) to determine short-intracortical inhibition (SICI) was investigated. To study the effect of different EEG processing, we compared the brain-state estimation deriving from three published methods. The influence of presence of neural oscillations was also investigated. To evaluate the effect of the brain-state on MEP and TEP features variability, we defined the brain-state based on specific EEG phase and power combinations, only in trials where neural oscillations were present. The relationship between TEPs and MEPs was further evaluated.The presence of neural oscillations resulted in more consistent results regardless of the EEG processing approach. Nonetheless, the latter still critically affected the outcomes, making conclusive claims complex. With our approach, the MEP amplitude was positively modulated by the alpha power and phase, with stronger responses during the trough phase and high power. Power and phase also affected TEP features. Importantly, similar effects were observed in both TMS conditions.These findings support the view that the brain state of alpha oscillations is associated with the variability observed in cortical and corticospinal responses to TMS, with a tight correlation between the two. The results further highlight the importance of closed-loop stimulation approaches while underlining that care is needed in designing experiments and choosing the analytical approaches, which should be based on knowledge from offline studies to control for the heterogeneity originating from different EEG processing strategies.
研究 alpha 振荡对皮质脊髓兴奋性影响的文献存在分歧。我们认为，这些发现的不一致性可能源于脑状态确定的脑电图 (EEG) 处理。在这里，我们进一步深入研究了脑状态对皮质和皮质脊髓兴奋性的影响，并量化了不同 EEG 处理的影响。皮质脊髓兴奋性通过经颅磁刺激 (TMS) 诱发的运动诱发电位 (MEP) 峰峰值幅度来测量；通过 TMS 诱发电位的 TEP 特征研究皮质反应。研究了 18 名年轻健康受试者的 TMS-EEG-肌电图 (EMG) 数据集，他们接受了 180 个单脉冲 (SP) 和 180 个成对脉冲 (PP) 以确定短程皮质内抑制 (SICI)。为了研究不同 EEG 处理的影响，我们比较了三种已发表方法得出的脑状态估计。还研究了神经振荡存在的影响。为了评估脑状态对 MEP 和 TEP 特征变异性的影响，我们仅在存在神经振荡的情况下，根据特定的 EEG 相位和功率组合定义脑状态。进一步评估了 TEP 和 MEP 之间的关系。无论 EEG 处理方法如何，神经振荡的存在都会导致更一致的结果。尽管如此，后者仍然严重影响了结果，使得得出结论变得复杂。使用我们的方法，MEP 幅度受 alpha 功率和相位的正向调节，在波谷相位和高功率时反应更强。功率和相位也影响 TEP 特征。重要的是，在两种 TMS 条件下都观察到了类似的效果。这些发现支持这样一种观点，即 alpha 振荡的脑状态与 TMS 对皮质和皮质脊髓反应的可变性有关，两者之间存在紧密的相关性。结果进一步强调了闭环刺激方法的重要性，同时强调在设计实验和选择分析方法时需要谨慎，这些方法应基于离线研究的知识，以控制源自不同 EEG 处理策略的异质性。
