Motor skill learning in Parkinson's disease.

The motor performance of patients with Parkinson's disease is degraded, but it is unclear whether their motor learning (adaptation learning and skill learning) ability is impaired. To assess the ability of these patients to learn motor tasks, we studied nine Parkinson's disease patients and eight age-matched normal (control) subjects who repetitively traced, as rapidly and accurately as possible, irregular geometric patterns with normal and mirror-reversed vision. The outcome was measured by statistical analysis and graphic plotting of values for actual and standardized performance variables and correlation of data from initial and final performance variables with indicators of disease severity. The results showed that, with normal vision, total movement time was reduced in both patients and normal subjects, but movement errors increased with repetition, apparently reflecting a speed-accuracy trade-off and adaptation learning. With mirror-reversed vision, total movement time and movement errors were reduced equally with repetition in both groups. These concomitant improvements in time and accuracy violate the rule of speed-accuracy trade-off and suggest that this behavior reflects true motor skill learning. We conclude that patients with Parkinson's disease do not differ from normal subjects in the processes of motor adaptation and motor skill learning.