Maeda Rodrigo S, Cluff Tyler, Gribble Paul L, Pruszynski J Andrew
Brain and Mind Institute, Western University, London, Ontario, Canada.
Robarts Research Institute, Western University, London, Ontario, Canada.
J Neurophysiol. 2017 Oct 1;118(4):1984-1997. doi: 10.1152/jn.00178.2017. Epub 2017 Jul 12.
Moving the arm is complicated by mechanical interactions that arise between limb segments. Such intersegmental dynamics cause torques applied at one joint to produce movement at multiple joints, and in turn, the only way to create single joint movement is by applying torques at multiple joints. We investigated whether the nervous system accounts for intersegmental limb dynamics across the shoulder, elbow, and wrist joints during self-initiated planar reaching and when countering external mechanical perturbations. Our first experiment tested whether the timing and amplitude of shoulder muscle activity account for interaction torques produced during single-joint elbow movements from different elbow initial orientations and over a range of movement speeds. We found that shoulder muscle activity reliably preceded movement onset and elbow agonist activity, and was scaled to compensate for the magnitude of interaction torques arising because of forearm rotation. Our second experiment tested whether elbow muscles compensate for interaction torques introduced by single-joint wrist movements. We found that elbow muscle activity preceded movement onset and wrist agonist muscle activity, and thus the nervous system predicted interaction torques arising because of hand rotation. Our third and fourth experiments tested whether shoulder muscles compensate for interaction torques introduced by different hand orientations during self-initiated elbow movements and to counter mechanical perturbations that caused pure elbow motion. We found that the nervous system predicted the amplitude and direction of interaction torques, appropriately scaling the amplitude of shoulder muscle activity during self-initiated elbow movements and rapid feedback control. Taken together, our results demonstrate that the nervous system robustly accounts for intersegmental dynamics and that the process is similar across the proximal to distal musculature of the arm as well as between feedforward (i.e., self-initiated) and feedback (i.e., reflexive) control. Intersegmental dynamics complicate the mapping between applied joint torques and the resulting joint motions. We provide evidence that the nervous system robustly predicts these intersegmental limb dynamics across the shoulder, elbow, and wrist joints during reaching and when countering external perturbations.
手臂的移动会因肢体节段之间产生的机械相互作用而变得复杂。这种节段间动力学使得作用于一个关节的扭矩会在多个关节产生运动，反过来，产生单关节运动的唯一方法是在多个关节施加扭矩。我们研究了在自发的平面伸手动作以及对抗外部机械扰动时，神经系统是否考虑了肩部、肘部和腕关节的节段间肢体动力学。我们的第一个实验测试了肩部肌肉活动的时间和幅度是否解释了在不同肘部初始方向和一系列运动速度下的单关节肘部运动中产生的相互作用扭矩。我们发现肩部肌肉活动可靠地先于运动开始和肘部主动肌活动，并且其大小会进行调整以补偿由于前臂旋转而产生的相互作用扭矩的大小。我们的第二个实验测试了肘部肌肉是否补偿单关节腕部运动引入的相互作用扭矩。我们发现肘部肌肉活动先于运动开始和腕部主动肌活动，因此神经系统预测了由于手部旋转而产生的相互作用扭矩。我们的第三个和第四个实验测试了在自发的肘部运动以及对抗导致纯肘部运动的机械扰动时，肩部肌肉是否补偿不同手部方向引入的相互作用扭矩。我们发现神经系统预测了相互作用扭矩的大小和方向，在自发的肘部运动和快速反馈控制过程中适当地调整了肩部肌肉活动的幅度。综合来看，我们的结果表明神经系统有力地考虑了节段间动力学，并且这个过程在手臂从近端到远端的肌肉组织中以及在前馈（即自发的）和反馈（即反射性的）控制之间是相似的。节段间动力学使施加的关节扭矩与产生的关节运动之间的映射变得复杂。我们提供的证据表明，在伸手动作以及对抗外部扰动时，神经系统有力地预测了肩部、肘部和腕关节的这些节段间肢体动力学。
