Hanajima Ritsuko, Shadmehr Reza, Ohminami Shinya, Tsutsumi Ryosuke, Shirota Yuichiro, Shimizu Takahiro, Tanaka Nobuyuki, Terao Yasuo, Tsuji Shoji, Ugawa Yoshikazu, Uchimura Motoaki, Inoue Masato, Kitazawa Shigeru
Department of Neurology, University of Tokyo Hospital, Tokyo, Japan; Department of Neurology, Kitasato University School of Medicine, Sagamihara, Kanagawa, Japan;
Laboratory for Computational Motor Control, Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, Maryland; and.
J Neurophysiol. 2015 Oct;114(4):2460-71. doi: 10.1152/jn.00145.2015. Epub 2015 Aug 26.
Cerebellar damage can profoundly impair human motor adaptation. For example, if reaching movements are perturbed abruptly, cerebellar damage impairs the ability to learn from the perturbation-induced errors. Interestingly, if the perturbation is imposed gradually over many trials, people with cerebellar damage may exhibit improved adaptation. However, this result is controversial, since the differential effects of gradual vs. abrupt protocols have not been observed in all studies. To examine this question, we recruited patients with pure cerebellar ataxia due to cerebellar cortical atrophy (n = 13) and asked them to reach to a target while viewing the scene through wedge prisms. The prisms were computer controlled, making it possible to impose the full perturbation abruptly in one trial, or build up the perturbation gradually over many trials. To control visual feedback, we employed shutter glasses that removed visual feedback during the reach, allowing us to measure trial-by-trial learning from error (termed error-sensitivity), and trial-by-trial decay of motor memory (termed forgetting). We found that the patients benefited significantly from the gradual protocol, improving their performance with respect to the abrupt protocol by exhibiting smaller errors during the exposure block, and producing larger aftereffects during the postexposure block. Trial-by-trial analysis suggested that this improvement was due to increased error-sensitivity in the gradual protocol. Therefore, cerebellar patients exhibited an improved ability to learn from error if they experienced those errors gradually. This improvement coincided with increased error-sensitivity and was present in both groups of subjects, suggesting that control of error-sensitivity may be spared despite cerebellar damage.
小脑损伤会严重损害人类的运动适应性。例如，如果伸手动作突然受到干扰，小脑损伤会损害从干扰引起的误差中学习的能力。有趣的是，如果在多次试验中逐渐施加干扰，小脑损伤患者可能会表现出更好的适应性。然而，这一结果存在争议，因为并非所有研究都观察到了逐渐与突然方案的不同效果。为了研究这个问题，我们招募了因小脑皮质萎缩导致单纯小脑共济失调的患者（n = 13），并要求他们在通过楔形棱镜观察场景的同时伸手去够一个目标。棱镜由计算机控制，使得在一次试验中突然施加全部干扰或在多次试验中逐渐增加干扰成为可能。为了控制视觉反馈，我们使用了快门眼镜，在伸手过程中去除视觉反馈，从而使我们能够逐次试验地测量从误差中学习的能力（称为误差敏感性）以及运动记忆的逐次试验衰退（称为遗忘）。我们发现，患者从逐渐方案中显著受益，相对于突然方案，他们在暴露阶段表现出更小的误差，在暴露后阶段产生更大的后效，从而提高了表现。逐次试验分析表明，这种改善是由于逐渐方案中误差敏感性的增加。因此，如果小脑患者逐渐经历这些误差，他们从误差中学习的能力会得到改善。这种改善与误差敏感性的增加同时出现，并且在两组受试者中都存在，这表明尽管小脑受损，但误差敏感性的控制可能未受影响。
