Criscimagna-Hemminger Sarah E, Bastian Amy J, Shadmehr Reza
Johns Hopkins University School of Medicine, 720 Rutland Ave., 416 Traylor Building, Baltimore, MD 21205, USA.
J Neurophysiol. 2010 Apr;103(4):2275-84. doi: 10.1152/jn.00822.2009. Epub 2010 Feb 17.
Small errors may affect the process of learning in a fundamentally different way than large errors. For example, adapting reaching movements in response to a small perturbation produces generalization patterns that are different from large perturbations. Are distinct neural mechanisms engaged in response to large versus small errors? Here, we examined the motor learning process in patients with severe degeneration of the cerebellum. Consistent with earlier reports, we found that the patients were profoundly impaired in adapting their motor commands during reaching movements in response to large, sudden perturbations. However, when the same magnitude perturbation was imposed gradually over many trials, the patients showed marked improvements, uncovering a latent ability to learn from errors. On sudden removal of the perturbation, the patients exhibited aftereffects that persisted much longer than did those in healthy controls. That is, despite cerebellar damage, the brain maintained the ability to learn from small errors and the motor memory that resulted from this learning was strongly resistant to change. Of note was the fact that on completion of learning, the motor output of the cerebellar patients remained distinct from healthy controls in terms of its temporal characteristics. Therefore cerebellar degeneration impaired the ability to learn from large-magnitude errors, but had a lesser impact on learning from small errors. The neural basis of motor learning in response to small and large errors appears to be distinct.
小错误可能会以与大错误截然不同的方式影响学习过程。例如，针对小扰动调整伸手动作会产生与大扰动不同的泛化模式。对大错误和小错误的反应是否涉及不同的神经机制？在这里，我们研究了小脑严重退化患者的运动学习过程。与早期报告一致，我们发现患者在对大的、突然的扰动做出反应时，在伸手动作过程中调整运动指令方面存在严重障碍。然而，当在多次试验中逐渐施加相同强度的扰动时，患者表现出明显的改善，揭示了从错误中学习的潜在能力。在突然去除扰动后，患者表现出的后效持续时间比健康对照组长得多。也就是说，尽管小脑受损，但大脑仍保持从小错误中学习的能力，并且这种学习产生的运动记忆对变化具有很强的抵抗力。值得注意的是，在学习完成后，小脑患者的运动输出在时间特征方面与健康对照组仍有明显差异。因此，小脑退化损害了从大强度错误中学习的能力，但对从小错误中学习的影响较小。对小错误和大错误做出反应的运动学习的神经基础似乎是不同的。
