Programming of a movement sequence in Parkinson's disease

The execution of multiple-component movements has been shown to be impaired in Parkinson's disease patients. To determine whether this deficit is attributed to faulty motor programming, a two-segment movement was examined by studying the kinematics of the first segment when the second segment contained variable accuracy requirements. The performance of 15 Parkinson's disease patients was compared with an age-matched control group. Movement precision not only affected the kinematics of the final segment but also the kinematics of the first segment. This 'context effect' was observed in both groups. Since Parkinson's disease patients revealed similar movement patterns to those of controls, their motor programming appears to be intact. Furthermore, correlation analysis for the segment movement-times revealed subjects with high as well as low correlation indices in both groups. The correlation indices were related to the context effect only in the Parkinson's disease patients. Independent of these phenomenon, Parkinson's disease patients showed marked hesitations between the movement segments compared with controls, suggesting that they have difficulty in implementing and/or in switching between motor program steps. Impaired force control and a reduced capacity to terminate movements in Parkinson's disease are discussed as possible explanations of the deficit in motor program implementation.