Division of Functional and Restorative Neurosurgery, Centre for Integrative Neuroscience, Eberhard Karls University, Tuebingen, Germany.
Division of Functional and Restorative Neurosurgery, Centre for Integrative Neuroscience, Eberhard Karls University, Tuebingen, Germany.
Brain Stimul. 2017 Nov-Dec;10(6):1055-1060. doi: 10.1016/j.brs.2017.07.009. Epub 2017 Jul 27.
Single transcranial magnetic stimulation (TMS) pulses activate different components of the motor cortex neural circuitry in a stimulation intensity-dependent way and may lead to a cumulative increase of corticospinal excitability (CSE) during the same stimulation session. Furthermore, transcranial alternating current stimulation (tACS) has been shown to increase in a frequency-specific way the level of CSE probed by single-pulse TMS. The interaction of these two phenomena, i.e. cumulative increases and baseline shifts of CSE, and the involved neural circuitry has not been studied yet.
The aim of this study was to investigate stimulation intensity-specific online effects of simultaneous TMS and tACS on CSE.
Single-pulse TMS was applied concurrent to 20 Hz tACS over the left primary motor cortex of thirteen healthy subjects to probe CSE indexed by motor evoked potentials (MEPs) recorded from the contralateral extensor carpi radialis muscle of the right hand during rest. Six different TMS intensities (90%, 100%, 110%, 120%, 130%, and 140% of resting motor threshold, RMT) were studied in a randomized blocked design. In each block, 40 pulses were applied with an inter-stimulus interval of 5 s and a jitter of ±0.5 s, i.e. at a stimulation frequency of 0.2-0.25 Hz.
Beta-tACS has a general facilitatory effect on CSE across the tested TMS intensities. The results of the block wise regression of the MEP amplitudes show a more specific effect. Combining tACS and TMS leads to a cumulative increase in CSE for the stimulation intensity of 120% RMT only (p = 0.0004).
CSE increases due to beta-tACS and cumulative TMS pulses may be mediated by different neuronal mechanisms.
单个经颅磁刺激（TMS）脉冲以刺激强度依赖的方式激活运动皮层神经回路的不同成分，并且在同一刺激过程中可能导致皮质脊髓兴奋性（CSE）的累积增加。此外，经颅交流电刺激（tACS）已被证明以频率特异性的方式增加单脉冲 TMS 探测到的 CSE 水平。这两种现象的相互作用，即 CSE 的累积增加和基线偏移，以及涉及的神经回路尚未得到研究。
本研究旨在研究同时 TMS 和 tACS 对 CSE 的刺激强度特异性在线影响。
在 13 名健康受试者的左侧初级运动皮层上同时施加单脉冲 TMS 和 20 Hz tACS，以在休息时记录右手对侧伸腕肌的运动诱发电位（MEP）来探测 CSE。在随机分组设计中研究了六个不同的 TMS 强度（90%、100%、110%、120%、130%和 140%的静息运动阈值，RMT）。在每个块中，以 5 秒的间隔和 ±0.5 秒的抖动施加 40 个脉冲，即刺激频率为 0.2-0.25 Hz。
β-tACS 对测试的 TMS 强度的 CSE 具有普遍的促进作用。MEP 幅度的块内回归结果显示出更具体的作用。TMS 和 tACS 的结合仅导致 120%RMT 的刺激强度下 CSE 的累积增加（p=0.0004）。
由于β-tACS 和累积 TMS 脉冲导致的 CSE 增加可能由不同的神经元机制介导。
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