Our long-range goal is to understand the role of the cerebellum in the control of reaching to grasp an object. The reach to grasp an object is a basic movement used in daily activities and production of a coordinated reach to grasp is highly dependent upon cerebellar function. Analyzing cerebellar participation in the reach to grasp will lead to much better understanding or the organization of the entire motor system and may provide valuable guidance to the design of prosthetic devices attempted to compensate for impaired motor control. We have discovered that cerebellar circuitry is specialized for the control of a reach to grasp. Simple movements of the forelimb do not activate cerebellar circuitry, but the coordinated action of reaching and grasping elicits high rates of neural discharge. We have also discovered that regions of the cerebellum are specialized for the control of specific components of the reach to grasp. Limb-related cerebellar output neurons only participate in the control of the grasping component and not the transport component of the movement. For a reach to grasp to accurately accomplish its behavioral goal, gras- related control signals need to be integrated with visual information concerning the spatial location and external features of the object to be grasped. This requires precise coordination between eye-related and limb- related neural networks. The working hypothesis that forms the basis for the proposed experiments is that the cerebellum is a critical part of the neural substrate underlying such coordination. Specifically, the experiments will test the idea that eye movement-relate cerebellar output neurons located ventrolaterally in posterior interpositus and adjacent parts of ventral dentate nucleus provide limb-related neural networks with information concerning the spatial location of the target to be grasped that is critical for the transport component of the reach to grasp to be accurate.
