Z'Graggen W J, Humm A M, Durisch N, Magistris M R, Rösler K M
Department of Neurology, Inselspital, University of Berne, Freiburgstrasse, CH-3010 Bern, Switzerland.
Clin Neurophysiol. 2005 Jul;116(7):1628-37. doi: 10.1016/j.clinph.2005.03.012.
To quantify repetitive discharges of spinal motor neurons (repMNDs) in response to single transcranial magnetic stimuli (TMS). To assess their contribution to the size of motor evoked potentials (MEPs).
We combined the triple stimulation technique (TST) with an additional nerve stimulus in the periphery (= quadruple stimulation; QuadS). The QuadS eliminates the first action potential descending on each axon after TMS, and eliminates effects on response size induced by desynchronization of these discharges, thereby allowing a quantification of motor neurons (MNs) discharging twice. In some instances, a quintuple stimulation (QuintS) was used, to quantify the number of MNs discharging three times. Recordings were from the abductor digiti minimi of 14 healthy subjects, using two different stimulation intensities and three different levels of facilitatory muscle pre-contractions.
The threshold to obtain repMNDs was high. Their maximal size differed markedly between subjects, ranging from 8 to 52% of all MNs. Stimulation intensity and facilitatory muscle contraction, but not resting motor threshold, correlated with the amount of repMNDs. QuintS never yielded discernible responses, hence all observed repMNDs were double discharges. RepMNDs contributed to the MEP areas, but did not influence MEP amplitudes.
QuadS and QuintS allow precise quantification of repMNDs. The threshold of repMNDs is high and varies considerably between subjects.
repMNDs have to be considered when MEP areas are measured. Their analysis may be of interest in neurological disorders, but standardized stimulation parameters appear essential.
量化脊髓运动神经元的重复性放电（repMNDs）对单次经颅磁刺激（TMS）的反应。评估它们对运动诱发电位（MEP）大小的贡献。
我们将三重刺激技术（TST）与外周额外的神经刺激相结合（即四重刺激；QuadS）。QuadS消除了TMS后每个轴突上下降的第一个动作电位，并消除了这些放电去同步化对反应大小的影响，从而能够量化放电两次的运动神经元（MNs）。在某些情况下，使用五重刺激（QuintS）来量化放电三次的MNs数量。记录来自14名健康受试者的小指展肌，使用两种不同的刺激强度和三种不同水平 的促进性肌肉预收缩。
获得repMNDs的阈值较高。它们的最大大小在受试者之间差异显著，范围为所有MNs的8%至52%。刺激强度和促进性肌肉收缩与repMNDs的数量相关，但静息运动阈值与之无关。QuintS从未产生可辨别的反应，因此所有观察到的repMNDs都是双重放电。repMNDs对MEP面积有贡献，但不影响MEP幅度。
QuadS和QuintS允许精确量化repMNDs。repMNDs的阈值较高，且在受试者之间差异很大。
在测量MEP面积时必须考虑repMNDs。它们的分析可能对神经系统疾病有意义，但标准化的刺激参数似乎至关重要。
