Latash Elizaveta M, Lecomte Charly G, Danner Simon M, Frigon Alain, Rybak Ilya A, Molkov Yaroslav I
Department of Mathematics and Statistics, Georgia State University, Atlanta, GA, United States.
Department of Pharmacology-Physiology, Université de Sherbrooke, Sherbrooke, QC, Canada.
Front Neurosci. 2020 Oct 16;14:598888. doi: 10.3389/fnins.2020.598888. eCollection 2020.
Rhythmic limb movements during locomotion are controlled by central pattern generator (CPG) circuits located in the spinal cord. It is considered that these circuits are composed of individual rhythm generators (RGs) for each limb interacting with each other through multiple commissural and long propriospinal circuits. The organization and operation of each RG are not fully understood, and different competing theories exist about interactions between its flexor and extensor components, as well as about left-right commissural interactions between the RGs. The central idea of circuit organization proposed in this study is that with an increase of excitatory input to each RG (or an increase in locomotor speed) the rhythmogenic mechanism of the RGs changes from "flexor-driven" rhythmicity to a "classical half-center" mechanism. We test this hypothesis using our experimental data on changes in duration of stance and swing phases in the intact and spinal cats walking on the ground or tied-belt treadmills (symmetric conditions) or split-belt treadmills with different left and right belt speeds (asymmetric conditions). We compare these experimental data with the results of mathematical modeling, in which simulated CPG circuits operate in similar symmetric and asymmetric conditions with matching or differing control drives to the left and right RGs. The obtained results support the proposed concept of state-dependent changes in RG operation and specific commissural interactions between the RGs. The performed simulations and mathematical analysis of model operation under different conditions provide new insights into CPG network organization and limb coordination during locomotion.
运动过程中的节律性肢体运动由位于脊髓的中枢模式发生器（CPG）回路控制。据认为，这些回路由每个肢体的单个节律发生器（RG）组成，它们通过多个连合和长脊髓固有回路相互作用。每个RG的组织和运作尚未完全了解，关于其屈肌和伸肌成分之间的相互作用以及RG之间的左右连合相互作用，存在不同的相互竞争的理论。本研究提出的回路组织的核心观点是，随着每个RG兴奋性输入的增加（或运动速度的增加），RG的节律产生机制从“屈肌驱动”节律转变为“经典半中枢”机制。我们使用关于完整和脊髓猫在地面行走或系腰带跑步机（对称条件）或左右带速不同的分裂带跑步机（不对称条件）上站立和摆动阶段持续时间变化的实验数据来检验这一假设。我们将这些实验数据与数学建模结果进行比较，在数学建模中，模拟的CPG回路在类似的对称和不对称条件下运行，对左右RG有匹配或不同的控制驱动。获得的结果支持了所提出的RG运作状态依赖性变化和RG之间特定连合相互作用的概念。在不同条件下对模型运作进行的模拟和数学分析为运动过程中CPG网络组织和肢体协调提供了新的见解。
