Perception and Motor Systems Laboratory, School of Human Movement Studies, University of Queensland, St Lucia, Brisbane, QLD, 4072, Australia.
Exp Brain Res. 2010 Jun;203(4):701-9. doi: 10.1007/s00221-010-2280-9. Epub 2010 May 9.
When people learn to reach in a novel sensorimotor environment, there are changes in the muscle activity required to achieve task goals. Here, we assessed the time course of changes in muscle directional tuning during acquisition of a new mapping between visual information and isometric force production in the absence of feedback-based error corrections. We also measured the influence of visuomotor adaptation on corticospinal excitability, to test whether any changes in muscle directional tuning are associated with adaptations in the final output components of the sensorimotor control system. Nine right-handed subjects performed a ballistic, center-out isometric target acquisition task with the right wrist (16 targets spaced every 22.5 degrees in the joint space). Surface electromyography was recorded from four major wrist muscles, and motor evoked potentials induced by transcranial magnetic stimulation were measured at baseline, after task execution in the absence of the rotation (A1), after adaptation to the rotation (B), and after a final block of trials without rotation (A2). Changes in the directional tuning of muscles closely matched the rotation of the directional error in force, indicating that the functional contribution of muscles remained consistent over the adaptation period. In contrast to previous motor learning studies, we found only minor changes in the amount of muscular activity and no increase in corticospinal excitability. These results suggest that increased muscle co-activation occurs only when the dynamics of the limb are perturbed and/or that online error corrections or altered force requirements are necessary to elicit a component of the adaptation in the final steps of the transformation between motor goal and muscle activation.
当人们学习在新的感觉运动环境中伸手时，为了达到任务目标，所需的肌肉活动会发生变化。在这里，我们评估了在没有基于反馈的错误校正的情况下，在视觉信息和等长力产生之间建立新映射的过程中，肌肉方向调谐的变化过程。我们还测量了视动适应对视皮质脊髓兴奋性的影响，以测试肌肉方向调谐的任何变化是否与感觉运动控制系统的最终输出组件的适应有关。九名右利手受试者使用右手腕进行了一项弹道式、中心外等距目标采集任务（关节空间中每 22.5 度有 16 个目标）。从四个主要腕部肌肉记录表面肌电图，并在基线、无旋转时执行任务后（A1）、适应旋转后（B）和无旋转最后一轮试验后（A2）测量经颅磁刺激诱导的运动诱发电位。肌肉的方向调谐变化与力的方向误差的旋转密切匹配，这表明在适应期间，肌肉的功能贡献保持一致。与之前的运动学习研究不同，我们发现肌肉活动量只有微小变化，皮质脊髓兴奋性没有增加。这些结果表明，只有当肢体的动力学受到干扰时，肌肉的共同激活才会增加，或者在线错误校正或改变力的要求是必要的，以在运动目标和肌肉激活之间的转换的最后步骤中引起适应的一部分。
