The basal ganglia, the cerebellum, and error correction in motor control

This dissertation combines methods from robotics, engineering control theory, the calculus of variations, and systems neuroscience to study the nature of the movement disorder in two neurologic illnesses: Huntington's disease (HD) and cerebellar dysfunction. The study of these motor disorders allows the simultaneous pursuit of two lofty goals. The first of these is to provide specific insights about the creation, improvement, or assessment of strategies for prevention, therapy, or rehabilitation of the disease. The second is to provide a better fundamental understanding of not only the disease processes but also of normal function of affected brain areas.; In simple point-to-point arm movements, we found that HD subjects often ended their movements in an irregular, jerky fashion. Analysis revealed that his elevated end-movement jerkiness seemed to be caused by poor online error correction. Specifically, we found that end-movement jerk, which was greatly increased overall in HD, varied substantially from trial to trial, but a large part of this variability was predicted by the magnitude of subtle, self-generated early-movement errors, and that the sensitivity of end-movement jerk to early-movement error was increased in HD. Not only were symptomatic HD subjects affected, but a majority of the clinically asymptomatic individuals gene-positive for HD as well, suggesting that dysfunction in error feedback control begins very early in the disease course, perhaps 7–10 years before clinical onset. When robotically generated force pulses were used to create randomly applied, externally generated perturbations, movements were sometimes completely destabilized in HD subjects but not controls or individuals with cerebellar dysfunction. This suggests the existence of an error feedback control deficit in HD for both internally and externally generated errors.; Subjects with HD displayed unimpaired trial-to-trial motor learning despite disturbed online error correction, while subjects with cerebellar degeneration showed greatly impaired motor learning but unimpaired online error correction. This dissociation indicates that the evaluation of sensory information to determine error is not generally disturbed in either HD or cerebellar dysfunction and suggests the existence of parallel neural pathways for processing error information as well as distinct but complementary roles for the basal ganglia and cerebellum in the control of movement. These data suggest that an important function of basal ganglia structures may be to support the correction of motor errors in flight, while an important function of the cerebellum may be to support the correction of errors form one trial to the next. (Abstract shortened by UMI.)...