THE BILATERAL REACH-TO-GRASP MOVEMENT OF PARKINSONS-DISEASE SUBJECTS

The performance of simultaneous movements is said to be disrupted in P arkinson's disease, yet there are some indications that this dysfuncti on is less evident for bilateral inter-limb actions, as opposed to uni lateral simultaneous actions. Focussing specifically upon natural acti ons, this study uses a three-dimensional kinematic system (ELITE) to a ssess the movement kinematics of a bilateral non-homologous reach-to-g rasp 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 reac hing to grasp the handle with the contralateral hand (precision grasp) . Overall the results indicated that Parkinson's disease subjects, lik e controls showed independent and appropriate kinematic parameterizati on each limb. For example, and as a reflection of task precision requi rements, 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 t o left upper limb inadequacies of Parkinson's disease subjects, were s uggested by findings of an earlier timing of maximum hand grip apertur e for the left than for the right hand, and adjustments to the final t ransport phase of the left arm under bilateral conditions. It is propo sed that left-right hand differences are more evident with basal gangl ia dysfunction, bur that these differences are compensated for by CNS mechanisms so that natural non-homologous reach-to-grasp actions are p erformed in a functional, coordinated and appropriate manner.