Tomita Yosuke, Feldman Anatol G, Levin Mindy F
School of Physical and Occupational Therapy, McGill University, Montreal, Quebec, Canada.
Centre for Interdisciplinary Research in Rehabilitation of Greater Montreal, Jewish Rehabilitation Hospital, Laval, Quebec, Canada.
J Neurophysiol. 2017 Jan 1;117(1):303-315. doi: 10.1152/jn.00292.2016. Epub 2016 Oct 26.
Motor actions may result from central changes in the referent body configuration, defined as the body posture at which muscles begin to be activated or deactivated. The actual body configuration deviates from the referent configuration, particularly because of body inertia and environmental forces. Within these constraints, the system tends to minimize the difference between these configurations. For pointing movement, this strategy can be expressed as the tendency to minimize the difference between the referent trajectory (R) and actual trajectory (Q) of the effector (hand). This process may underlie motor equivalent behavior that maintains the pointing trajectory regardless of the number of body segments involved. We tested the hypothesis that the minimization process is used to produce pointing in standing subjects. With eyes closed, 10 subjects reached from a standing position to a remembered target located beyond arm length. In randomly chosen trials, hip flexion was unexpectedly prevented, forcing subjects to take a step during pointing to prevent falling. The task was repeated when subjects were instructed to intentionally take a step during pointing. In most cases, reaching accuracy and trajectory curvature were preserved due to adaptive condition-specific changes in interjoint coordination. Results suggest that referent control and the minimization process associated with it may underlie motor equivalence in pointing.
NEW & NOTEWORTHY: Motor actions may result from minimization of the deflection of the actual body configuration from the centrally specified referent body configuration, in the limits of neuromuscular and environmental constraints. The minimization process may maintain reaching trajectory and accuracy regardless of the number of body segments involved (motor equivalence), as confirmed in this study of reaching from standing in young healthy individuals. Results suggest that the referent control process may underlie motor equivalence in reaching.
运动动作可能源于参考身体构型的中枢变化，参考身体构型定义为肌肉开始激活或失活时的身体姿势。实际身体构型会偏离参考构型，尤其是由于身体惯性和环境力的影响。在这些限制条件下，系统倾向于使这些构型之间的差异最小化。对于指向运动，这种策略可以表示为使效应器（手）的参考轨迹（R）和实际轨迹（Q）之间的差异最小化的倾向。这一过程可能是运动等效行为的基础，该行为可保持指向轨迹，而不论所涉及的身体节段数量。我们测试了这样一个假设，即最小化过程用于使站立的受试者产生指向动作。受试者闭眼，从站立姿势伸向一个位于手臂长度之外的记忆目标。在随机选择的试验中，意外地阻止了髋部屈曲，迫使受试者在指向过程中迈出一步以防止摔倒。当指示受试者在指向过程中故意迈出一步时，重复该任务。在大多数情况下，由于关节间协调的适应性特定条件变化，伸手准确性和轨迹曲率得以保留。结果表明，参考控制及其相关的最小化过程可能是指向运动中运动等效的基础。
在神经肌肉和环境限制范围内，运动动作可能源于实际身体构型相对于中枢指定的参考身体构型的偏差最小化。如在这项针对年轻健康个体站立伸手的研究中所证实的，最小化过程可能保持伸手轨迹和准确性，而不论所涉及的身体节段数量（运动等效）。结果表明，参考控制过程可能是伸手运动中运动等效的基础。
