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 participation still remains to be clarified. This paper examines the proposal that the basal ganglia may serve to scale the amplitude of limb movements, with basal-ganglia dysfunction leading to the inappropriate scaling of intended motor activity. Several authors have suggested that examining the loss of function in Parkinson's-disease (PD) patients offers perhaps the best way of learning about the role played by the basal ganglia in human motor function. While it has previously been reported that PD patients underscale the transport phase of their reach-to grasp movements, it has generally been assumed that the grasp component is normal. In this paper we demonstrate, using a group of hemiparkinson patients, that the scaling of the grasp component is also underscaled in PD patients.