van den Bos Mehdi A J, Geevasinga Nimeshan, Menon Parvathi, Burke David, Kiernan Matthew C, Vucic Steve
Sydney Medical School, University of Sydney, Sydney, Australia.
Department of Neurology, Westmead Hospital, New South Wales, Australia.
J Neurophysiol. 2017 Mar 1;117(3):1156-1162. doi: 10.1152/jn.00832.2016. Epub 2016 Dec 28.
Voluntary contraction leads to facilitation of motor-evoked potentials (MEPs) producing greater amplitude, shorter onset latency, and prolonged duration of the electromyography potential. Whereas hyperexcitability of spinal motoneurons and changes in descending corticospinal volleys have been proposed as putative mechanisms for changes in MEP amplitude and onset latency, a contribution of propriospinal interneurons, exerting modulatory effects on α-motoneurons, has been proposed as a potential explanation for prolongation of MEP duration. The aim of the present study is to gain further insight into the physiological processes underlying changes in MEP duration. Transcranial magnetic stimulation (TMS) studies were undertaken on 30 healthy controls, using a 90-mm circular coil, with MEPs recorded at rest and during facilitation, produced by contraction of abductor pollicis brevis. In the same experiment, short interval-intracortical inhibition (SICI) was recorded at rest. Facilitation resulted in a significant prolongation of MEP duration, which increased with stimulus intensity and was accompanied by an increase in MEP amplitude. The main effect (TMS intensity × activation state) was correlated with MEP duration ( = 10.9, < 0.001), whereas TMS intensity ( = 30.5, < 0.001) and activation state ( = 125.8, < 0.001) in isolation were correlated with MEP amplitude. There was a significant inverse relationship between SICI and MEP duration at rest (R = 0.141, = 0.041) and during facilitation (R = 0.340, = 0.001). The present findings suggest that similar physiological processes mediate changes in the facilitated MEP duration and amplitude and that both cortical and nonpropriospinal spinal mechanisms contribute to changes in MEP duration. Muscle contraction is associated with a significant increase in motor-evoked potential (MEP) duration and amplitude. Whereas the increase in MEP duration was linear, the amplitude increase exhibited a ceiling effect. Importantly, the MEP duration increase strongly correlated with short interval-intracortical inhibition, a biomarker of motor cortical function. This suggests that whereas similar physiological processes contribute to changes in facilitated MEP duration and amplitude, cortical mechanisms appear to contribute to MEP duration changes.
自主收缩会导致运动诱发电位（MEP）的易化，使肌电图电位的幅度增大、起始潜伏期缩短且持续时间延长。虽然脊髓运动神经元的兴奋性过高以及皮质脊髓下行冲动的变化被认为是MEP幅度和起始潜伏期变化的潜在机制，但脊髓中间神经元对α运动神经元发挥调节作用，被认为是MEP持续时间延长的一个潜在解释。本研究的目的是进一步深入了解MEP持续时间变化背后的生理过程。对30名健康对照者进行经颅磁刺激（TMS）研究，使用90毫米圆形线圈，在静息状态和由拇短展肌收缩产生的易化过程中记录MEP。在同一实验中，静息时记录短间隔皮质内抑制（SICI）。易化导致MEP持续时间显著延长，其随刺激强度增加而增加，并伴有MEP幅度增加。主要效应（TMS强度×激活状态）与MEP持续时间相关（r = 10.9，P < 0.001），而单独的TMS强度（r = 30.5，P < 0.001）和激活状态（r = 125.8，P < 0.001）与MEP幅度相关。静息时（R = 0.141，P = 0.041）和易化过程中（R = 0.340，P = 0.001），SICI与MEP持续时间之间存在显著的负相关关系。目前的研究结果表明，相似的生理过程介导了易化MEP持续时间和幅度的变化，并且皮质和非脊髓性脊髓机制都对MEP持续时间的变化有贡献。肌肉收缩与运动诱发电位（MEP）持续时间和幅度的显著增加有关。虽然MEP持续时间的增加是线性的，但幅度增加呈现出天花板效应。重要的是，MEP持续时间的增加与短间隔皮质内抑制密切相关，短间隔皮质内抑制是运动皮质功能的一个生物标志物。这表明，虽然相似的生理过程导致了易化MEP持续时间和幅度的变化，但皮质机制似乎对MEP持续时间变化有贡献。
