Yokoyama Hikaru, Hagio Kohtaroh, Ogawa Tetsuya, Nakazawa Kimitaka
Laboratory of Sports Sciences, Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan.
Japan Society for the Promotion of Science, Chiyoda-ku, Tokyo, Japan.
Physiol Rep. 2017 Nov;5(22). doi: 10.14814/phy2.13504.
Coordinated locomotor muscle activity is generated by the spinal central pattern generators (CPGs), which are modulated by peripheral and supraspinal inputs. The CPGs would consist of multiple motor modules generating basic muscle activity, which are distributed rostrocaudally along the spinal cord. To activate the motor modules in proper sequence, rostrocaudally traveling waves of activation in the spinal cord are important mechanisms in the CPGs. The traveling waves of activation have been observed in nonhuman vertebrates. However, they have not yet been confirmed during human locomotion. Although, rostrocaudal wave-like activations in the spinal cord were observed during walking in humans in a previous study, the propagation shifted rostrally toward the upper lumbar segments at foot contact. Here, using an air stepping task to remove the foot-contact interactions, we examined whether the traveling wave mechanism exists in the human spinal circuits based on the activation sequence of motor modules and their topography. We measured electromyographic activity of lower leg muscles during the air-stepping task. Then, we extracted motor modules (i.e., basic patterns of sets of muscle activations: muscle synergies) from the measured muscle activities using nonnegative matrix factorization method. Next, we reconstructed motoneuron (MN) activity from each module activity based on myotomal charts. We identified four types of motor modules from muscle activities during the air-stepping task. Each motor module represented different sets of synergistic muscle activations. MN clusters innervating each motor module were sequentially activated from the rostral to caudal region in the spinal cord, from the initial flexion to the last extension phase during air-stepping. The rostrocaudally sequential activation of MN clusters suggests the possibility that rostrocaudally traveling waves exist in human locomotor spinal circuits. The present results advance the understanding of human locomotor control mechanisms, and provide important insights into the evolution of locomotor networks in vertebrates.
协调性的运动肌肉活动由脊髓中央模式发生器（CPG）产生，而CPG受外周和脊髓上输入的调节。CPG由多个产生基本肌肉活动的运动模块组成，这些模块沿脊髓前后分布。为了按适当顺序激活运动模块，脊髓中前后传播的激活波是CPG中的重要机制。在非人类脊椎动物中已观察到激活波。然而，在人类运动过程中尚未得到证实。尽管在先前的一项研究中，在人类行走时观察到脊髓中有前后波状激活，但在足部接触时，传播方向向前移向腰上段。在这里，我们使用空中踏步任务来消除足部接触的相互作用，基于运动模块的激活顺序及其拓扑结构，研究人类脊髓回路中是否存在传播波机制。我们测量了空中踏步任务期间小腿肌肉的肌电图活动。然后，我们使用非负矩阵分解方法从测量的肌肉活动中提取运动模块（即肌肉激活集的基本模式：肌肉协同作用）。接下来，我们根据肌节图从每个模块活动中重建运动神经元（MN）活动。我们从空中踏步任务期间的肌肉活动中识别出四种类型的运动模块。每个运动模块代表不同的协同肌肉激活集。在脊髓中，支配每个运动模块的MN簇从头部到尾部区域依次被激活，从空中踏步的初始屈曲阶段到最后伸展阶段。MN簇的前后顺序激活表明人类运动脊髓回路中可能存在前后传播波。目前的结果推进了对人类运动控制机制的理解，并为脊椎动物运动网络的进化提供了重要见解。
