Data_Sheet_1_Local Differences in Cortical Excitability – A Systematic Mapping Study of the TMS-Evoked N100 Component.PDF

Transcranial magnetic stimulation (TMS) with simultaneous electroencephalography applied to the primary motor cortex provides two parameters for cortical excitability: motor evoked potentials (MEPs) and TMS-evoked potentials (TEPs). This study aimed to evaluate the effects of systematic coil shifts on both the TEP N100 component and MEPs in addition to the relationship between both parameters. In 12 healthy adults, the center of a standardized grid was fixed above the hot spot of the target muscle of the left primary motor cortex. Twelve additional positions were arranged in a quadratic grid with positions between 5 and 10 mm from the hot spot. At each of the 13 positions, TMS single pulses were applied. The topographical maximum of the resulting N100 was located ipsilateral and slightly posterior to the stimulation site. A source analysis revealed an equivalent dipole localized more deeply than standard motor cortex coordinates that could not be explained by a single seeded primary motor cortex dipole. The N100 topography might not only reflect primary motor cortex activation, but also sum activation of the surrounding cortex. N100 amplitude and latency decreased significantly during stimulation anterior-medial to the hot spot although MEP amplitudes were smaller at all other stimulation sites. Therefore, N100 amplitudes might be suitable for detecting differences in local cortical excitability. The N100 topography, with its maximum located posterior to the stimulation site, possibly depends on both anatomical characteristics of the stimulated cortex and differences in local excitability of surrounding cortical areas. The less excitable anterior cortex might contribute to a more posterior maximum. There was no correlation between N100 and MEP amplitudes, but a single-trial analysis revealed a trend toward larger N100 amplitudes in trials with larger MEPs. Thus, functionally efficient cortical excitation might increase the probability of higher N100 amplitudes, but TEPs are also generated in the absence of MEPs.

将同步记录脑电图（Electroencephalography, EEG）的经颅磁刺激（Transcranial Magnetic Stimulation, TMS）技术应用于初级运动皮层，可获取皮层兴奋性的两项核心参数：运动诱发电位（Motor Evoked Potentials, MEPs）与经颅磁刺激诱发电位（TMS-evoked Potentials, TEPs）。本研究旨在系统评估线圈位移对TEP的N100成分及MEPs的影响，同时探究两项参数间的关联。
本研究招募12名健康成年受试者，将标准化网格的中心固定于左侧初级运动皮层对应靶肌肉的运动热点上方。在距离该热点5至10毫米的范围内，以方形网格布局额外设置12个刺激位点。在全部13个位点（含中心热点）均施加单次TMS脉冲。
结果显示，所记录的N100成分的脑电地形图峰值位于刺激位点同侧且略偏后位置。源定位分析发现，等效偶极子的深度较标准初级运动皮层坐标更深，且无法通过单个预置的初级运动皮层偶极子模型解释。
N100的脑电地形分布或许不仅反映初级运动皮层的激活，还可汇总周围皮层的激活信号。在热点前内侧区域进行刺激时，N100的波幅与潜伏期均显著降低；而在其余所有刺激位点，MEP波幅均相对更小。据此推测，N100波幅或可用于检测局部皮层兴奋性的差异。
N100的脑电地形分布（其峰值位于刺激位点后方）可能同时受刺激皮层的解剖学特征，以及周围皮层区域局部兴奋性差异的影响。兴奋性较低的前侧皮层或许会促使峰值位置更靠后。
本研究未发现N100与MEP的波幅之间存在显著相关性，但单试次分析显示，在MEP波幅更大的试次中，N100波幅存在升高的趋势。由此可见，功能高效的皮层兴奋或可提升N100波幅升高的概率，但即便未诱发MEPs，同样可产生TEPs。