Department of Neurophysiology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo 187-8502, Japan;
Department of Developmental Physiology, National Institute for Physiological Sciences, Aichi 444-8585, Japan.
Proc Natl Acad Sci U S A. 2017 Aug 8;114(32):8643-8648. doi: 10.1073/pnas.1704328114. Epub 2017 Jul 24.
Grasping is a highly complex movement that requires the coordination of multiple hand joints and muscles. Muscle synergies have been proposed to be the functional building blocks that coordinate such complex motor behaviors, but little is known about how they are implemented in the central nervous system. Here we demonstrate that premotor interneurons (PreM-INs) in the primate cervical spinal cord underlie the spatiotemporal patterns of hand muscle synergies during a voluntary grasping task. Using spike-triggered averaging of hand muscle activity, we found that the muscle fields of PreM-INs were not uniformly distributed across hand muscles but rather distributed as clusters corresponding to muscle synergies. Moreover, although individual PreM-INs have divergent activation patterns, the population activity of PreM-INs reflects the temporal activation of muscle synergies. These findings demonstrate that spinal PreM-INs underlie the muscle coordination required for voluntary hand movements in primates. Given the evolution of neural control of primate hand functions, we suggest that spinal premotor circuits provide the fundamental coordination of multiple joints and muscles upon which more fractionated control is achieved by superimposed, phylogenetically newer, pathways.
抓握是一种高度复杂的运动，需要多个手部关节和肌肉的协调。肌肉协同作用被认为是协调这种复杂运动行为的功能构建块，但对于它们在中枢神经系统中是如何实现的知之甚少。在这里，我们证明灵长类动物颈脊髓中的运动前神经元（PreM-INs）是在自愿抓握任务中手肌肉协同作用的时空模式的基础。通过对手部肌肉活动的尖峰触发平均，我们发现 PreM-INs 的肌肉区域不是均匀分布在手肌肉上，而是分布为与肌肉协同作用相对应的簇。此外，尽管单个 PreM-INs 具有不同的激活模式，但 PreM-INs 的群体活动反映了肌肉协同作用的时间激活。这些发现表明，脊髓 PreM-INs 是灵长类动物自愿手部运动所需的肌肉协调的基础。鉴于灵长类动物手部功能的神经控制的进化，我们认为脊髓运动前回路提供了多个关节和肌肉的基本协调，通过叠加的、进化更新的途径实现了更细分的控制。
