Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, USA.
J Neurophysiol. 2013 Jul;110(2):322-33. doi: 10.1152/jn.00745.2012. Epub 2013 Apr 17.
Cerebellar damage impairs the control of complex dynamics during reaching movements. It also impairs learning of predictable dynamic perturbations through an error-based process. Prior work suggests that there are distinct neural mechanisms involved in error-based learning that depend on the size of error experienced. This is based, in part, on the observation that people with cerebellar degeneration may have an intact ability to learn from small errors. Here we studied the relative effect of specific dynamic perturbations and error size on motor learning of a reaching movement in patients with cerebellar damage. We also studied generalization of learning within different coordinate systems (hand vs. joint space). Contrary to our expectation, we found that error size did not alter cerebellar patients' ability to learn the force field. Instead, the direction of the force field affected patients' ability to learn, regardless of whether the force perturbations were introduced gradually (small error) or abruptly (large error). Patients performed best in fields that helped them compensate for movement dynamics associated with reaching. However, they showed much more limited generalization patterns than control subjects, indicating that patients rely on a different learning mechanism. We suggest that patients typically use a compensatory strategy to counteract movement dynamics. They may learn to relax this compensatory strategy when the external perturbation is favorable to counteracting their movement dynamics, and improve reaching performance. Altogether, these findings show that dynamics affect learning in cerebellar patients more than error size.
小脑损伤会影响在进行伸臂运动时对复杂动力学的控制，也会影响通过基于误差的过程来学习可预测的动力学干扰。之前的研究表明，基于误差的学习涉及到不同的神经机制，这些机制取决于所经历的误差大小。这部分基于这样一个观察结果，即小脑退化的人可能具有从较小误差中学习的完整能力。在这里，我们研究了特定动力学干扰和误差大小对小脑损伤患者伸臂运动学习的相对影响。我们还研究了在不同坐标系（手坐标系与关节坐标系）内学习的泛化。与我们的预期相反，我们发现误差大小并不能改变小脑损伤患者学习力场的能力。相反，力场的方向影响了患者学习的能力，而与力干扰是逐渐引入（小误差）还是突然引入（大误差）无关。患者在有助于补偿与伸臂运动相关的运动动力学的力场中表现最佳。然而，他们表现出的泛化模式比对照组要局限得多，这表明患者依赖于不同的学习机制。我们认为，患者通常使用补偿策略来抵消运动动力学。当外部干扰有利于抵消他们的运动动力学时，他们可能会学会放松这种补偿策略，并提高伸臂表现。总之，这些发现表明，动力学对小脑损伤患者的学习影响比误差大小更大。
