Sobell Department of Motor Neuroscience and Movement Disorders, University College London, London, United Kingdom; Non-invasive Brain Stimulation Unit, IRCCS Santa Lucia Foundation, Rome, Italy.
Sobell Department of Motor Neuroscience and Movement Disorders, University College London, London, United Kingdom.
Brain Stimul. 2018 Sep-Oct;11(5):1063-1070. doi: 10.1016/j.brs.2018.04.015. Epub 2018 Apr 24.
the influence of pulse width, pulse waveform and current direction on transcranial magnetic stimulation (TMS) outcomes is of critical importance. However, their effects have only been investigated indirectly with motor-evoked potentials (MEP). By combining TMS and EEG it is possible to examine how these factors affect evoked activity from the cortex and compare that with the effects on MEP.
we used a new controllable TMS device (cTMS) to vary systematically pulse width, pulse waveform and current direction and explore their effects on global and local TMS-evoked EEG response.
In 19 healthy volunteers we measured (1) resting motor threshold (RMT) as an estimate of corticospinal excitability; (2) global mean field power (GMFP) as an estimate of global cortical excitability; and (3) local mean field power (LMFP) as an estimate of local cortical excitability.
RMT was lower with monophasic posterior-to-anterior (PA) pulses that have a longer pulse width (p < 0.001). After adjusting for the individual motor threshold of each pulse type we found that (a) GMFP was higher with monophasic pulses (p < 0.001); (b) LMFP was higher with longer pulse width (p = 0.015); (c) early TEP polarity was modulated depending on the current direction (p = 0.01).
Despite normalizing stimulus intensity to RMT, we found that local and global responses to TMS vary depending on pulse parameters. Since EEG responses can vary independently of the MEP, titrating parameters of TMS in relation to MEP threshold is not a useful way of ensuring that a constant set of neurons is activated within a cortical area.
脉冲宽度、脉冲波形和电流方向对经颅磁刺激（TMS）结果的影响至关重要。然而，它们的影响仅通过运动诱发电位（MEP）间接进行了研究。通过将 TMS 和 EEG 相结合，可以检查这些因素如何影响皮质的诱发电活动，并将其与 MEP 的影响进行比较。
我们使用新型可控 TMS 设备（cTMS）系统地改变脉冲宽度、脉冲波形和电流方向，并探索它们对全局和局部 TMS 诱发 EEG 反应的影响。
在 19 名健康志愿者中，我们测量了（1）静息运动阈值（RMT）作为皮质脊髓兴奋性的估计值；（2）全局平均场功率（GMFP）作为皮质整体兴奋性的估计值；和（3）局部平均场功率（LMFP）作为皮质局部兴奋性的估计值。
单相后前（PA）脉冲的 RMT 较低，且具有较长的脉冲宽度（p < 0.001）。在调整每种脉冲类型的个体运动阈值后，我们发现（a）单相脉冲的 GMFP 较高（p < 0.001）；（b）随着脉冲宽度的增加 LMFP 更高（p = 0.015）；（c）TEP 的早期极性取决于电流方向（p = 0.01）。
尽管将刺激强度归一化为 RMT，但我们发现 TMS 的局部和全局反应会因脉冲参数而有所不同。由于 EEG 反应可以独立于 MEP 变化，因此根据 MEP 阈值调整 TMS 参数并不是确保在皮质区域内激活一组恒定神经元的有效方法。
