Learning manual pursuit tracking skills in patients with Parkinson's disease

Evidence from a number of sources identifies the putamen and its ultimate cortical projection sites as forming a possible substrate for motor learning. The present paper describes two experiments which explored motor learning of a pursuit tracking task under first (position) and second (velocity) order control dynamics, in patients with Parkinson's disease on and off (experiment 2 only) their normal dopaminergic medication. In neither experiment did the medicated patients show evidence of significant impairment in learning the tasks. In the velocity tracking task, however, the patients off medication showed significantly less improvement in performance with practice. The discussion considers a number of possible interpretations of this finding. Contemporary cognitive theories of motor learning consider behavioural change with practice to be the combined action of an automatic procedural system, together with input from a conscious declarative system. Development of declarative knowledge about the task may have changed the nature of the process involved, from a visually guided task to a more predictive one based upon an internal representation. Evidence from various sources suggests that patients with Parkinson's disease have particular problems with this mode of control, thus making the task more difficult. It is suggested that motor control deficits have not been adequately considered in previous studies on motor learning, and that the evidence from clinical studies for a role of the putamen/supplementay motor area in motor learning remains equivocal.