Prolonged practice is of scarce benefit in improving motor performance in Parkinson's disease

Many studies have addressed practice effects in motor sequences in Parkinson's disease (PD). Most studied short-term practice and showed that treated patients with mild-to-moderate disease achieve normal or slightly abnormal improvement. Less attention has focused on practice effects after prolonged training (days), and the results are inconclusive. Here, we studied the kinematic changes induced by prolonged practice in a group of medicated patients with mild-to-moderate PD and a healthy control group. We did so by analyzing an internally determined sequential arm movement performed as fast and accurately as possible before and after a 2-week training period. After 1-day's practice, movement duration, pause duration, and movement accuracy improved similarly in patients and controls, indicating that patients benefitted normally from short-term practice. After 1-week's practice, movement and pause duration improved further in both groups, whereas movement accuracy remained unchanged. After 2-weeks' practice, healthy controls continued to improve but patients did not, indicating reduced prolonged practice benefit in PD. Because short-term practice benefit on motor performance is thought to be mediated predominantly by cerebellar activation, whereas long-term practice benefit relies predominantly on the basal ganglia, we attribute our findings to the underlying basal ganglia dysfunction in PD. Our study may be relevant for planning and executing rehabilitation programs in these patients.