Adaptive mechanisms in the control of interlimb coordination during locomotion

当在不断变化的环境中航行时，肢体间协调对于动态稳定性和改变运动速度至关重要，涉及中枢神经系统不同水平的复杂动态相互作用和肌肉骨骼系统的紧急特性。尽管肢体间协调的动态控制具有明显的重要性，但在陆地哺乳动物中却定义不清。我的研究计划的长期目标是阐明运动过程中控制肢体间协调的神经生理学和生物力学机制。为了实现这一目标，训练猫在具有四个独立表面的跑步机上行走，从而独立地控制前肢和后肢或左侧和右侧的速度。皮带可以以相同的速度（系紧皮带运动）或不同的速度（分裂皮带运动）运行。因此，肢体之间的速度或速度差异可以被系统地操纵，以挑战肢体间的协调，揭示适应机制。慢性运动被用来记录肌肉活动和唤起反射，而三维运动捕捉获取详细的运动运动学。在完整的和脊髓横断的猫进行比较，以确定在协调四肢的脊柱机制的贡献。第一个目标是表征在系带和分裂带运动期间的反射调制。反射对于快速适应外部干扰至关重要。我们假设，反射幅度1）将调制任务和2）将是一步一步的基础上，在分裂带运动。我们还假设，结果将是相似的，在完整的和脊髓猫，表明反射调制主要是在脊髓水平。第二个目的是描述捆绑带和分裂带运动过程中肌肉活动的模式。我们假设：1）肌肉协同作用利用了某些肌肉的双功能性质，2）协同作用可以扩展到不止一个肢体，3）它们主要在脊柱水平控制。第三个目标是描述束缚带和分裂带运动中肢体内部和之间的动态协调。我们假设，interlimb协调自我组织时，调整速度和限制施加在interlimb模式。这项研究将为控制运动过程中肢体间协调的神经力学机制提供新的理解深度。这是特别重要的，因为知识的神经和生物力学系统如何相互作用，以动态协调肢体在真实的运动是至关重要的设计生物逼真的机器人和有效的神经假肢设备，以及最大限度地提高运动性能和运动康复。

Interlimb coordination is essential for dynamic stability when navigating in an ever-changing environment and to change locomotor speed, involving complex dynamic interactions at different levels of the central nervous system and emergent properties of the musculoskeletal system. Despite its obvious importance, the dynamic control of interlimb coordination is poorly defined in terrestrial mammals. The long-term goal of my research program is to elucidate neurophysiological and biomechanical mechanisms that control interlimb coordination during locomotion. To accomplish this goal, cats are trained to step on a treadmill with four separate surfaces whereby the speed of the forelimbs and hindlimbs or of the left and right sides are independently controlled. The belts can operate at the same speed (tied-belt locomotion) or at different speeds (split-belt locomotion). Thus, speed or speed differences between limbs can be systematically manipulated to challenge interlimb coordination, revealing adaptive mechanisms. Chronic implantations are used to record muscle activity and evoke reflexes while three-dimensional motion capture acquires detailed locomotor kinematics. Comparisons are made in intact and spinal-transected cats to define the contribution of spinal mechanisms in coordinating the limbs. The FIRST OBJECTIVE is to characterize reflex modulation during tied-belt and split-belt locomotion. Reflexes are essential to quickly adjust to external perturbations. We hypothesize that reflex amplitude 1) will be modulated with task and 2) will be less variable on a step-by-step basis during split-belt locomotion. We also hypothesize that results will be similar in intact and spinal cats, indicating that reflex modulation is primarily determined at a spinal level. The SECOND OBJECTIVE is to characterize patterns of muscle activity during tied-belt and split-belt locomotion. We hypothesize that 1) muscle synergies make use of the bifunctional nature of some muscles, 2) synergies can extend to more than one limb and 3) they are primarily controlled at a spinal level. The THIRD OBJECTIVE is to characterize the dynamic coordination within and between limbs during tied-belt and split-belt locomotion. We hypothesize that interlimb coordination self-organizes when adjusting to speed and to constraints imposed on the interlimb pattern. The proposed research will provide a new depth of understanding on the neuromechanical mechanisms that control interlimb coordination during locomotion. This is of particular significance because knowledge of how the neural and biomechanical systems interact to dynamically coordinate the limbs during real movements is crucial for designing biologically realistic robots and efficient neuroprosthetic devices as well as for maximizing athletic performance and motor rehabilitation.