Institute for General Kinesiology and Exercise Science, Faculty of Sports Science, University of Leipzig, Leipzig, 04109, Germany; Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, 04103, Germany.
Institute for General Kinesiology and Exercise Science, Faculty of Sports Science, University of Leipzig, Leipzig, 04109, Germany; Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, 04103, Germany.
Neuroscience. 2019 May 15;406:300-313. doi: 10.1016/j.neuroscience.2019.03.029. Epub 2019 Mar 21.
Mirror Activity (MA) is a phenomenon that is characterized by involuntarily occurring muscular activity in homologous contralateral limbs during unilateral movements. Even in neurologically healthy humans, MA of a small extent has been described, which does not directly lead to visible movements, but nonetheless, it is still detectable with surface electromyography (EMG) and therefore defined as physiological MA (pMA). The present study investigated latency- and amplitude-characteristics of pMA during repetitive unimanual isometric contractions with high but constant force requirements (80% maximum force). Here, we show for the first time that pMA is not time-locked to the muscle onset of voluntarily contracting hand muscles but starts with varying and dynamically changing latencies. Following consecutive isometric unilateral contractions, the latency of pMA progressively decreases accompanied by a progressive linear increase in its amplitude possibly as a result of changes in inhibitory mechanisms involved in suppressing involuntarily occurring muscular activity. Overall, the latency and amplitude of pMA show a strong inverse relationship. Furthermore, based on the previously proposed hypothesis of motor overflow, we explored the possibility of pMA modulation through anodal and cathodal transcranial direct current stimulation (tDCS) applied to the ipsilateral primary motor cortex (M1), relative to a voluntarily contracting hand. Neither anodal nor cathodal tDCS is able to modulate amplitude or latency of pMA compared to sham tDCS. In conclusion, our results extend the existing knowledge of pMA occurring due to high-effort unilateral contractions with constant force requirements to the aspect of its latency and the inverse association with its amplitude.
镜像活动（MA）是一种现象，其特征是在单侧运动过程中，同源对侧肢体出现无意识的肌肉活动。即使在神经健康的人中，也已经描述了很小程度的 MA，它不会直接导致可见的运动，但仍然可以通过表面肌电图（EMG）检测到，因此被定义为生理性 MA（pMA）。本研究调查了在高但恒定的力要求（80%最大力）下进行重复单侧等长收缩时 pMA 的潜伏期和幅度特征。在这里，我们首次表明，pMA 与自愿收缩手部肌肉的肌肉起始时间不同步，而是以不同且动态变化的潜伏期开始。在连续进行单侧等长收缩后，pMA 的潜伏期逐渐缩短，其幅度逐渐线性增加，可能是由于抑制涉及抑制无意识肌肉活动的抑制机制发生变化所致。总体而言，pMA 的潜伏期和幅度呈强负相关。此外，基于运动溢出的先前提出的假设，我们探索了通过同侧初级运动皮层（M1）的阳极和阴极经颅直流电刺激（tDCS）调节 pMA 的可能性，与自愿收缩的手相对。与假刺激相比，阳极和阴极 tDCS 均不能调节 pMA 的幅度或潜伏期。总之，我们的结果将具有恒定力要求的高努力单侧收缩引起的 pMA 的现有知识扩展到其潜伏期方面及其与幅度的反比关系。
