The bilateral reach-to-grasp movement of Parkinson's disease subjects

The performance of simultaneous movements is said to be disrupted in Parkinson's disease, yet there are some indications that this dysfunction is less evident for bilateral inter-limb actions, as opposed to unilateral simultaneous actions. Focussing specifically upon natural actions, this study uses a three-dimensional kinematics system (ELITE) to assess the movement kinematics of a bilateral non-homologous reach-to-grasp action. The target device consisted of a large cylinder (diameter 8 cm) to which a handle (diameter 0.8 cm) was attached. The task was to reach and grasp the cylinder with one hand (gross grasp) while reaching to grasp the handle with the contralateral hand (precision grasp). Overall the results indicated that Parkinson's disease subjects, like controls, showed independent and appropriate kinematic parameterization of each limb. For example, and as a reflection of task precision requirements, the time taken to decelerate upon the item to be grasped was longer for the limb grasping the handle than for the limb grasping the cylinder. Subtle indications of compensatory mechanisms, in response to left upper limb inadequacies of Parkinson's disease subjects, were suggested by findings of an earlier timing of maximum hand grip aperture for the left than for the right hand, and adjustments to the final transport phase of the left arm under bilateral conditions. It is proposed that left-right hand differences are more evident with basal ganglia dysfunction, but that these differences are compensated for by CNS mechanisms so that natural non-homologous reach-to-grasp actions are performed in a functional, coordinated and appropriate manner.