Talis V L, Kazennikov O V, Castellote J M, Grishin A A, Ioffe M E
Institute for Information Transmission Problems, Russian Academy of Science, Moscow, Russian Federation,
Exp Brain Res. 2014 Mar;232(3):803-10. doi: 10.1007/s00221-013-3789-5. Epub 2013 Dec 6.
Motor evoked potentials (MEPs) in the right first dorsal interosseous (FDI) muscle elicited by transcranial magnetic stimulation of left motor cortex were assessed in ten healthy subjects during maintenance of a fixed FDI contraction level. Subjects maintained an integrated EMG (IEMG) level with visual feedback and reproduced this level by memory afterwards in the following tasks: stationary FDI muscle contraction at the level of 40 ± 5 % of its maximum voluntary contraction (MVC; 40 % task), at the level of 20 ± 5 % MVC (20 % task), and also when 20 % MVC was preceded by either no contraction (0-20 task), by stronger muscle contraction (40-20 task) or by no contraction with a previous strong contraction (40-0-20 task). The results show that the IEMG level was within the prescribed limits when 20 and 40 % stationary tasks were executed with and without visual feedback. In 0-20, 40-20, and 40-0-20 tasks, 20 % IEMG level was precisely controlled in the presence of visual feedback, but without visual feedback the IEMG and force during 20 % IEMG maintenance were significantly higher in the 40-0-20 task than those in 0-20 and 40-20 tasks. That is, without visual feedback, there were significant variations in muscle activity due to different prehistory of contraction. In stationary tasks, MEP amplitudes in 40 % task were higher than in 20 % task. MEPs did not differ significantly during maintenance of the 20 % level in tasks with different prehistory of muscle contraction with and without visual feedback. Thus, in spite of variations in muscle background activity due to different prehistory of contraction MEPs did not vary significantly. This dissociation suggests that the voluntary maintenance of IEMG level is determined not only by cortical mechanisms, as reflected by corticospinal excitability, but also by lower levels of CNS, where afferent signals and influences from other brain structures and spinal cord are convergent.
在十名健康受试者维持固定的右手第一背侧骨间肌（FDI）收缩水平期间，评估了经颅磁刺激左侧运动皮层所诱发的右侧FDI肌肉的运动诱发电位（MEP）。受试者通过视觉反馈维持肌电图积分（IEMG）水平，并在随后的任务中凭记忆重现该水平：FDI肌肉在其最大自主收缩（MVC）的40±5%水平进行静态收缩（40%任务），在20±5%MVC水平进行静态收缩（20%任务），以及在20%MVC之前分别为无收缩（0 - 20任务）、更强的肌肉收缩（40 - 20任务）或先有一次强烈收缩后无收缩（40 - 0 - 20任务）的情况。结果表明，在有和没有视觉反馈的情况下执行20%和40%静态任务时，IEMG水平均在规定范围内。在0 - 20、40 - 20和40 - 0 - 20任务中，在有视觉反馈时，20%IEMG水平得到精确控制，但在没有视觉反馈时，40 - 0 - 20任务中20%IEMG维持期间的IEMG和力量显著高于0 - 20和40 - 20任务。也就是说，在没有视觉反馈时，由于不同的收缩既往史，肌肉活动存在显著差异。在静态任务中，40%任务中的MEP波幅高于20%任务。在有和没有视觉反馈的情况下，在不同肌肉收缩既往史的任务中维持20%水平期间，MEP没有显著差异。因此，尽管由于不同的收缩既往史肌肉背景活动存在差异，但MEP没有显著变化。这种分离表明，IEMG水平的自主维持不仅由皮质机制决定，如皮质脊髓兴奋性所反映的那样，还由中枢神经系统的较低水平决定，在这些较低水平中，传入信号以及来自其他脑结构和脊髓的影响相互汇聚。
