ABSTRACT

Objective: The aim of the study was to show that short-lasting (90 s) transcranial alternating current stimulation (tACS) at 20 Hz delivered over the left primary motor cortex (M1) is able to change the shape of recruitment curve of the corticospinal pathway.

Methods: The corticospinal pathway was studied during tACS by means of the relationship between the intensity of transcranial magnetic stimulation (TMS) delivered over the left M1 and corresponding motor evoked potentials (MEPs) recorded from the right first dorsal interosseus muscle (FDI), in nine healthy subjects. In order to extract characteristics of the input–output relationship that have particular physiological relevance, data were fitted to the Boltzmann sigmoidal function by the Levenberg–Marquardt nonlinear, least mean squares algorithm.

Results: The β-rhythm tACS influenced the shape and parameters of the input–output relation, so that the initial segment of the conditioned curve (from threshold to 30% of maximum muscle size) diverged, while the subsequent segment converged to overlap the unconditioned control curve.

Discussion: β-rhythm tACS conditions only a definite subset of corticospinal elements influencing less than 30% of the entire motoneuronal pool. The fact that β-rhythm tACS mainly affects the most excitable motoneurons could explain the observed antikinetic effect of the tACS at β-rhythm applied in the motor regions.

摘要

目的：研究的目的是显示在左主运动皮层（M1）上以20 Hz的持续时间（90 s）经颅交流电刺激（tACS）能够改变皮质脊髓的募集曲线的形状途径。

方法：通过左M1上传递的颅磁刺激（TMS）的强度与右背背骨间肌（FDI）记录的相应的运动诱发电位（MEPs）之间的关系研究tACS期间的皮质脊髓途径。九个健康受试者。为了提取具有特殊生理相关性的输入-输出关系的特征，通过Levenberg-Marquardt非线性最小均方算法将数据拟合到Boltzmann Sigmoidal函数。

结果：β节奏tACS影响输入输出关系的形状和参数，以使条件曲线的初始部分（从阈值到最大肌肉大小的30％）发散，而随后的部分收敛以覆盖未调节的部分控制曲线。

讨论：β-节奏tACS仅能影响一定比例的皮质脊髓型元素，而影响的比例少于整个动脑神经元池的30％。β-节律tACS主要影响最易激发的运动神经元这一事实可以解释tACS在运动区应用β-节律时观察到的抗运动作用。