Motoneuron responsiveness to corticospinal tract stimulation during the silent period induced by transcranial magnetic stimulation
Motoneuron responsiveness to corticospinal tract stimulation during the silent period induced by transcranial magnetic stimulation
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经颅磁刺激诱发的静默期运动神经元对皮质脊髓束刺激的反应
DOI：
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发表时间：
2016
影响因子：
2
通讯作者：
Chris J. McNeil
中科院分区：
文献类型：
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作者：
Alexandra F. Yacyshyn;Emma Woo;Maggie C. Price;Chris J. McNeil
基于H反射数据，脊髓机制被认为是经颅磁刺激(TMS)诱导的静默期的前50-80ms的机制。由于一些方法学问题可能影响H反射作为运动神经元兴奋性的测量方法的有效性，本研究使用经乳突刺激在静止期诱发颈髓运动诱发电位(CMEPs)。11例随访1~3次，其中32例或44例(S 3例)在最大扭矩为25%时发生肘屈肌等长收缩。在每次收缩过程中，分别给予经乳突刺激以诱发非条件性CMEP，并在TMS后以50至150毫秒的刺激间隔(ISIS)来诱发条件性CMEP。TMS和经乳突刺激的刺激强度分别为静默期~200ms和非条件性CMEP最大复合肌肉动作电位(MMAX)的15%、50%或85%。在所有ISIS和经乳突部刺激强度下，条件性CMEP显著小于非条件性CMEP(P<0.001)。然而，与15%或50%的Mmax相比，条件性CMEP的抑制在85%显著减少(p=0.001)。与已发表的H反射数据相反，条件化CMEP没有在50-80毫秒内恢复，在测试的最长ISI(150毫秒)时仍显著抑制。这些数据表明，TMS诱发的静默期的脊髓部分比以前报道的要长得多。与周围神经刺激不同，经乳突刺激不影响本体感传入运动神经元。因此，相对于H反射，由于TMS诱导的肌肉抽动，CMEP将受到更大的传入介导的停滞和抑制。
Based on H-reflex data, spinal mechanisms are proposed to be responsible for the first 50–80 ms of the transcranial magnetic stimulation (TMS)-induced silent period. As several methodological issues can compromise H-reflex validity as a measure of motoneuron excitability, this study used transmastoid stimulation to elicit cervicomedullary motor evoked potentials (CMEPs) during the silent period. Eleven subjects made 1–3 visits which involved 32 or 44 brief (~3 s) isometric elbow flexor contractions at 25 % of maximal torque. During each contraction, transmastoid stimulation was delivered in isolation to elicit an unconditioned CMEP and at interstimulus intervals (ISIs) ranging from 50 to 150 ms after TMS to elicit a conditioned CMEP. Stimulus intensities for TMS and transmastoid stimulation were set to elicit a silent period of ~200 ms and an unconditioned CMEP of 15, 50, or 85 % of the maximal compound muscle action potential (Mmax), respectively. At all ISIs and intensities of transmastoid stimulation, the conditioned CMEP was significantly smaller than the unconditioned CMEP (p < 0.001). However, suppression of the conditioned CMEP was significantly less at 85 % compared to 15 or 50 % Mmax (p = 0.001). Contrary to published H-reflex data, the conditioned CMEP did not recover within 50–80 ms, remaining significantly suppressed at the longest ISI tested (150 ms). These data suggest the spinal portion of the TMS-evoked silent period is considerably longer than reported previously. Transmastoid stimulation, unlike peripheral nerve stimulation, does not impact proprioceptive inflow to motoneurons. Hence, relative to the H-reflex, the CMEP will be subjected to greater afferent-mediated disfacilitation and inhibition due to the TMS-induced muscle twitch.