Motion imagery in Parkinson's disease.

Patients with Parkinson's disease fail to fully profit from advance information about a target's movement in tracking tasks, possibly indicating deficient anticipation of the target's movement. Time estimation has been claimed to be deficient in Parkinson's disease. On the background of these studies, we tested the hypothesis that motion imagery is impaired in Parkinson's disease. Eleven non-demented patients with Parkinson's disease and nine age-matched controls participated in experiments testing their ability to anticipate trajectories of moving points (prediction whether two moving points would crash or not) and to estimate the time needed for completion of an invisible target's movement (a point moving around a circle). In addition, mirror drawing, a task involving motor learning and adjustment of movement to incongruent visual feedback, was tested. The Parkinson's disease patients, who failed to improve on mirror drawing, were not impaired on the imagery tasks: they estimated movement time and predicted trajectories with equal precision as the controls. Motion imagery thus appears to be intact in Parkinson's disease. However, Parkinson's disease patients did not accelerate their predictions of trajectories with practice as fast as the controls, a deficit which may be interpreted in terms of the fronto-striatal dysfunction repeatedly demonstrated in Parkinson's disease.