Department of Neurology, Johns Hopkins Medical School, Baltimore, Maryland 21205, USA, and Kennedy Krieger Institute, Baltimore, Maryland 21205, USA
Address for correspondence: Amy J. Bastian, Kennedy Krieger Institute, 707 North Broadway, G05, Baltimore, MD 21205. Voice: 443-923-2718; fax: 443-923-2715.
bastian{at}kennedykrieger.org
Ann. N.Y. Acad. Sci. 978: 16-27 (2002).
Our work has been focused on understanding the mechanism of
movement abnormalities associated with cerebellar ataxia. The
hypothesis tested is that the cerebellum acts to modulate muscle
activity across multiple joints in anticipation of the mechanical
interaction torques generated by one's own movement and by external
forces. Individuals with cerebellar damage were studied in two
sets of experiments. In the first experiment, we studied how
cerebellar subjects' movement changed when interaction torques
were present, and then reduced via mechanically constraining
movement to a single joint. Consistent with the hypothesis,
it was found that cerebellar endpoint errors were greatly improved
when interaction torques were reduced. We also found that cerebellar
deficits in the unconstrained condition were not explained by
a general failure of torque timing or magnitude scaling. This
supports the idea that the cerebellum plays a specific and important
role in adjusting for the dynamics of one's own body movements.
In the second experiment, we studied how well cerebellar subjects
could adapt arm movements to external loads. Cerebellar subjects
were tested as they adapted a catching movement to balls of
different weight. It was found that they were slow or unable
to adapt through practice and did not show evidence of storage
of the adaptation. This suggests that the cerebellum is needed
for rapid adaptations for loads in movement. Given these findings,
we think that the cerebellum is important in anticipating and
adjusting for the mechanical demands of movement though trial-and-error
practice.
