Precision grip deficits in cerebellar disorders in man

Objective: To investigate the effect of a variety of cerebellar pathologies on a functional motor task lifting an object in a precision grip). Methods: The study involved 8 patients with unilateral damage in the region of the posterior inferior cerebellar artery (PICA), 6 with damage in the r egion of the superior cerebellar artery (SUPCA), 12 patients with familiar or idiopathic cortical cerebellar degeneration, and 45 age-matched normal s ubjects. Subjects lifted an object of unpredictable load (internally guided task) or responded to a sudden load increase while holding the object stea dily (externally guided task). Results: Damage to the dentate nucleus (SUPCA) or its afferent input (cereb ellar atrophy) resulted in disruption of the close coordination normally se en between proximal muscles (lifting the object) and the fingers (gripping the object) during a self-paced lift. Both the SUPCA,roup and, more markedl y, the atrophy group, showed exaggerated levels of grip force. All patients showed a normal rate of grip force development. Damage in the PICA region had no significant effect on any of the measured lifting parameters. All pa tient groups retained the ability to scale grip force to different object l oads. The automatic grip force response to unexpected load increase of a ha nd held object showed normal latency and time course in all patient groups. The response was modulated by the rate of the load change. Response magnit ude was exaggerated in the atrophy patients at all 3 rates tested. Conclusions: Disturbances associated with cerebellar disorders differed fro m those seen following damage to the basal ganglia, with no evidence of slo wed rates of grip force development. Disruption of temporal coordination be tween the proximal muscles (lifting) and the fingers (gripping) in a lift w as apparent, supporting the role of the cerebellum in coordinating the timi ng of multi-joint movement sequences. Exaggeration of grip force levels was found in association with damage to the dentate nucleus or, in particular, to its afferent input. This could support a role or the cerebellum in sens orimotor processing, but might also represent a failure to time correctly t he duration of grip force generation. (C) 2001 Elsevier Science Ireland Ltd . All rights reserved.