Deficits in sensorimotor control during precise hand movements in Huntington's disease.

OBJECTIVES To investigate the performance of patients with Huntington's disease (HD) while manipulating objects using a precision grip. METHODS The grip forces developed by the fingers were studied while subjects lifted an object of unpredictable weight in the hand. The ability to stabilize grip force after externally imposed weight change was also studied. RESULTS Patients used higher grip forces than the normal subjects in both the lifting and holding phases, particularly with a lighter weight. Lift timing was slowed in the patients, most markedly with a lighter weight. Increased levels of inter-trial variation were observed only with a light weight. This indicates that the slowing in HD differs from that in Parkinson's disease, which remains constant regardless of object load, and that the slowing in HD is not due to involuntary antagonist muscle activity resulting from an underlying chorea. The grip force response to sudden weight change was normal, but appeared after a delay which increased at lower rates of weight change. CONCLUSIONS Disturbances in precision grip timing and magnitude in HD may result from a reduced ability to process relevant tactile afferent input. The delay in the adaptive response suggests an increased threshold for detection of weight change in HD. Alternatively, this delay may arise from mediation of the response over an additional cerebellar pathway to compensate for damage to the basal ganglia.