Learning in people with cerebellar damage

While damage to the cerebellum can make control of movements very difficult, this report provides new evidence that even the damaged cerebellum has a latent mechanism of learning: it learns better when movement errors are kept small, but is quite impaired if the errors are large.

Program Grant holders Shigeru Kitazawa and Reza Shadmehr and colleagues
authored on Tue, 01 December 2015

Over the past two decades, it has been established that the human cerebellum is critical for motor adaptation. As the cerebellum degrades because of genetic or vascular damage, patients exhibit numerous motor disorders, for which there are currently no effective therapies. A potential therapy has been rehabilitation, but because the cerebellum is necessary for motor adaptation, even this therapy is not available to the cerebellar patients.

Figure:  Healthy people and individuals with cerebellar disease were instructed to reach for a target while viewing it through computer controlled prism glasses.  A. The distortion caused by the prism glasses was abruptly introduced on trial number 30.  Whereas the healthy individuals adapted to this distortion, the patients were severely impaired.  B. The distortion was introduced gradually.  The cerebellar patients were much less impaired in adapting to this perturbation.

Here, the authors report that patients with cerebellar damage can learn to improve their movements, but only if the patterns of training are restricted to small errors.  Therefore, the damaged cerebellum could preferentially learn from small errors.  Importantly, the study was able to uncover the mechanism with which the cerebellar patients were benefiting from the small errors.  Mathematical analysis of the data demonstrated that the patients, as well as healthy controls, increased their error-sensitivity when faced with small errors, but down-regulated error-sensitivity when the errors became larger.                                      

From a basic science perspective, this work provides evidence that despite cerebellar damage, the brain can perform motor learning.  From a clinical perspective, the work points to a rehabilitation strategy that will be of particular benefit to patients for whom there are currently no effective therapies.

People who suffer from cerebellar disease often face a bleak perspective: there are currently no effective drugs to halt progression of the disease.  A possibility to slow the progression of the disease is rehabilitation, but even this approach is difficult in cerebellar disease because motor learning, the basis of rehabilitation, can be severely impaired with cerebellar dysfunction.  In this paper, we find that motor learning can be improved in cerebellar disease under certain conditions which involve reduction of the motor errors.  If these results are confirmed and expanded, it may result in new rehabilitation approaches for treatment of cerebellar disorders.

Reference

Modulation of error-sensitivity during a prism adaptation task in people with cerebellar degeneration. Ritsuko Hanajima, Reza Shadmehr, Shinaya Ohminami, Ryosuke Tsutsumi, Yuichiro Shirota, Takahiro Shimizu, Nobuyuki Tanaka, Yasuo Terao, Shoji Tsuji, Yoshikazu Ugawa, Motoaki Uchimura, Masato Inoue, and Shigeru Kitazawa (2015) Journal of Neurophysiology, 114:2460-2471.

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