de Rugy Aymar, Hinder Mark R, Woolley Daniel G, Carson Richard G
Perception and Motor Systems Laboratory, School of Human Movement Studies, Room 424, Building 26, University of Queensland, St Lucia QLD, 4072, Australia.
J Neurophysiol. 2009 May;101(5):2263-9. doi: 10.1152/jn.90898.2008. Epub 2009 Feb 18.
Reaching to visual targets engages the nervous system in a series of transformations between sensory information and motor commands. That which remains to be determined is the extent to which the processes that mediate sensorimotor adaptation to novel environments engage neural circuits that represent the required movement in joint-based or muscle-based coordinate systems. We sought to establish the contribution of these alternative representations to the process of visuomotor adaptation. To do so we applied a visuomotor rotation during a center-out isometric torque production task that involved flexion/extension and supination/pronation at the elbow-joint complex. In separate sessions, distinct half-quadrant rotations (i.e., 45 degrees ) were applied such that adaptation could be achieved either by only rescaling the individual joint torques (i.e., the visual target and torque target remained in the same quadrant) or by additionally requiring torque reversal at a contributing joint (i.e., the visual target and torque target were in different quadrants). Analysis of the time course of directional errors revealed that the degree of adaptation was lower (by approximately 20%) when reversals in the direction of joint torques were required. It has been established previously that in this task space, a transition between supination and pronation requires the engagement of a different set of muscle synergists, whereas in a transition between flexion and extension no such change is required. The additional observation that the initial level of adaptation was lower and the subsequent aftereffects were smaller, for trials that involved a pronation-supination transition than for those that involved a flexion-extension transition, supports the conclusion that the process of adaptation engaged, at least in part, neural circuits that represent the required motor output in a muscle-based coordinate system.
视觉目标的定位会使神经系统在感觉信息和运动指令之间进行一系列转换。尚待确定的是，介导对新环境的感觉运动适应的过程在多大程度上涉及在基于关节或基于肌肉的坐标系中表征所需运动的神经回路。我们试图确定这些不同表征对视觉运动适应过程的贡献。为此，我们在一项中心向外等长扭矩产生任务中应用了视觉运动旋转，该任务涉及肘关节复合体的屈伸和旋前/旋后。在不同的实验环节中，施加了不同的半象限旋转（即45度），这样可以通过仅重新调整各个关节扭矩（即视觉目标和扭矩目标保持在同一象限）或额外要求在一个起作用的关节处扭矩反转（即视觉目标和扭矩目标在不同象限）来实现适应。对方向误差时间进程的分析表明，当需要关节扭矩方向反转时，适应程度较低（约低20%）。此前已经确定，在这个任务空间中，旋前和旋后的转换需要不同的一组肌肉协同肌参与，而在屈伸转换中则不需要这种变化。额外的观察结果表明，与涉及屈伸转换的试验相比，涉及旋前-旋后转换的试验的初始适应水平较低且随后的后效应较小，这支持了这样的结论：适应过程至少部分涉及在基于肌肉的坐标系中表征所需运动输出的神经回路。
