The control of bimanual reach-to-grasp movements in hemiparkinsonian patients

The basal ganglia are thought to participate in the control and programming of a variety of motor behaviours. However, the precise nature of this part icipation still remains to be clarified. This paper examines the proposal t hat the basal ganglia may serve to scale the amplitude of limb movements, w ith basal-ganglia dysfunction leading to the inappropriate scaling of inten ded motor activity. Several authors have suggested that examining the loss of function in Parkinson's-disease (PD) patients offers perhaps the best wa y of learning about the role played by the basal ganglia in human motor fun ction. While it has previously been reported that PD patients underscale th e transport phase of their reach-to grasp movements, it has generally been assumed that the grasp component is normal. In this paper we demonstrate, u sing a group of hemiparkinson patients, that the scaling of the grasp compo nent is also underscaled in PD patients.