BACKGROUND the use of combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) for the functional evaluation of the cerebral cortex in health and disease is becoming increasingly common. However, there is still some ambiguity regarding the extent to which brain responses to auditory and somatosensory stimulation contribute to the TMS-evoked potential (TEP). OBJECTIVE/HYPOTHESIS to measure separately the contribution of auditory and somatosensory stimulation caused by TMS, and to assess their contribution to the TEP waveform, when stimulating the motor cortex (M1). METHODS 19 healthy volunteers underwent 7 blocks of EEG recording. To assess the impact of auditory stimulation on the TEP waveform, we used a standard figure of eight coil, with or without masking with a continuous noise reproducing the specific time-varying frequencies of the TMS click, stimulating at 90% of resting motor threshold. To further characterise auditory responses due to the TMS click, we used either a standard or a sham figure of eight coil placed on a pasteboard cylinder that rested on the scalp, with or without masking. Lastly, we used electrical stimulation of the scalp to investigate the possible contribution of somatosensory activation. RESULTS auditory stimulation induced a known pattern of responses in electrodes located around the vertex, which could be suppressed by appropriate noise masking. Electrical stimulation of the scalp alone only induced similar, non-specific scalp responses in the in the central electrodes. TMS, coupled with appropriate masking of sensory input, resulted in specific, lateralized responses at the stimulation site, lasting around 300 ms. CONCLUSIONS if careful control of confounding sources is applied, TMS over M1 can generate genuine, lateralized EEG activity. By contrast, sensory evoked responses, if present, are represented by non-specific, late (100-200 ms) components, located at the vertex, possibly due to saliency of the stimuli. Notably, the latter can confound the TEP if masking procedures are not properly used.

中文翻译：

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由于皮层和外周激活，解开脑电图对 TMS 的反应

背景 联合经颅磁刺激 (TMS) 和脑电图 (EEG) 在健康和疾病中用于大脑皮层功能评估的使用正变得越来越普遍。然而，关于大脑对听觉和体感刺激的反应对 TMS 诱发电位 (TEP) 的贡献程度仍然存在一些歧义。目标/假设分别测量由 TMS 引起的听觉和体感刺激的贡献，并评估它们在刺激运动皮层 (M1) 时对 TEP 波形的贡献。方法 19 名健康志愿者接受了 7 次脑电图记录。为了评估听觉刺激对 TEP 波形的影响，我们使用了一个标准的八线圈数字，使用或不使用连续噪声进行掩蔽，再现 TMS 咔嗒声的特定时变频率，在 90% 的静息运动阈值下进行刺激。为了进一步表征由于 TMS 咔哒声引起的听觉反应，我们使用了标准或假冒的 8 个线圈，放置在放置在头皮上的粘贴板圆柱体上，有或没有掩蔽。最后，我们使用头皮的电刺激来研究体感激活的可能贡献。结果听觉刺激在位于顶点周围的电极中诱导了一种已知的反应模式，这可以通过适当的噪声掩蔽来抑制。单独对头皮的电刺激仅在中央电极中引起类似的、非特异性的头皮反应。TMS，加上适当的感官输入掩蔽，导致特定的，刺激部位的侧化反应，持续约 300 毫秒。结论如果仔细控制混杂来源，M1 上的 TMS 可以产生真正的、侧化的 EEG 活动。相比之下，感官诱发反应（如果存在）由位于顶点的非特异性、晚期（100-200 毫秒）分量表示，可能是由于刺激的显着性。值得注意的是，如果未正确使用掩蔽程序，后者会混淆 TEP。