Smooth pursuit during dose-related on-off fluctuations in Parkinson's disease

Smooth pursuit was studied during predictable L-dopa dose-related "off" periods of morning akinesia and wearing off and during "on" periods in eight patients with idiopathic Parkinson's disease. Smooth pursuit gain was significantly reduced in patients during both on and off phases. Despite marked fluctuations between parkinsonism and periods of near normal skeletal motion, there were no changes in smooth pursuit gain. We conclude that unvarying paresis of smooth pursuit in Parkinson's disease signifies involvement of neural circuits that are distinct from the dopaminergic mechanisms that mediate the on-off phenomenon of somatic motor control.