BACKGROUND Transcranial magnetic stimulation (TMS) evokes voltage deflections in electroencephalographic (EEG) recordings, known as TMS-evoked potentials (TEPs), which are increasingly used to study brain dynamics. However, the extent to which TEPs reflect activity directly evoked by magnetic rather than sensory stimulation is unclear. OBJECTIVE To characterize and minimize the contribution of sensory inputs to TEPs. METHODS Twenty-four healthy participants received TMS over the motor cortex using two different intensities (below and above cortical motor threshold) and waveforms (monophasic, biphasic). TMS was also applied over the shoulder as a multisensory control condition. Common sensory attenuation measures, including coil padding and noise masking, were adopted. We examined spatiotemporal relationships between the EEG responses to the scalp and shoulder stimulations at sensor and source levels. Furthermore, we compared three different filters (independent component analysis, signal-space projection with source informed reconstruction (SSP-SIR) and linear regression) designed to attenuate the impact of sensory inputs on TEPs. RESULTS The responses to the scalp and shoulder stimulations were correlated in both temporal and spatial domains, especially after ∼60 ms, regardless of the intensity and stimuli waveform. Among the three filters, SSP-SIR showed the best trade-off between removing sensoryrelated signals while preserving data not related to the control condition. CONCLUSIONS The findings demonstrate that TEPs elicited by motor cortex TMS reflect a combination of transcranially and peripherally evoked brain responses despite adopting sensory attenuation methods during experiments, thereby highlighting the importance of adopting sensory control conditions in TMS-EEG studies. Offline filters may help to isolate the transcranial component of the TEP from its peripheral component, but only if these components express different spatiotemporal patterns. More realistic control conditions may help to improve the characterization and attenuation of sensory inputs to TEPs, especially in early responses.

中文翻译：

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表征和最小化感觉输入对 TMS 诱发电位的贡献

背景经颅磁刺激 (TMS) 引起脑电图 (EEG) 记录中的电压偏转，称为 TMS 诱发电位 (TEP)，其越来越多地用于研究脑动力学。然而，TEP 反映由磁刺激而不是感官刺激直接引起的活动的程度尚不清楚。目标表征和最小化感官输入对 TEP 的贡献。方法 24 名健康参与者使用两种不同的强度（低于和高于皮质运动阈值）和波形（单相、双相）在运动皮层接受 TMS。TMS 也应用于肩部作为多感官控制条件。采用了常见的感官衰减措施，包括线圈填充和噪声屏蔽。我们在传感器和源级别检查了 EEG 对头皮和肩部刺激的反应之间的时空关系。此外，我们比较了旨在减弱感官输入对 TEP 影响的三种不同滤波器（独立分量分析、信号空间投影与源信息重建 (SSP-SIR) 和线性回归）。结果无论强度和刺激波形如何，对头皮和肩部刺激的反应在时间和空间域中都相关，尤其是在约 60 毫秒之后。在三个滤波器中，SSP-SIR 在去除感官相关信号和保留与控制条件无关的数据之间取得了最佳平衡。结论 研究结果表明，尽管在实验过程中采用了感觉衰减方法，但运动皮层 TMS 引起的 TEP 反映了经颅和外周诱发的大脑反应的组合，从而突出了在 TMS-EEG 研究中采用感觉控制条件的重要性。离线过滤器可能有助于将 TEP 的经颅成分与其外围成分隔离，但前提是这些成分表达不同的时空模式。更现实的控制条件可能有助于改善对 TEP 的感官输入的表征和衰减，尤其是在早期反应中。离线过滤器可能有助于将 TEP 的经颅成分与其外围成分隔离，但前提是这些成分表达不同的时空模式。更现实的控制条件可能有助于改善对 TEP 的感官输入的表征和衰减，尤其是在早期反应中。离线过滤器可能有助于将 TEP 的经颅成分与其外围成分隔离，但前提是这些成分表达不同的时空模式。更现实的控制条件可能有助于改善对 TEP 的感官输入的表征和衰减，尤其是在早期反应中。