Studies of parkinsonian movement: 1. Programming and execution of eye movements

Rapid voluntary eye movements in bradykinetic parkinsonian patients and normal subjects were recorded when the movement was executed with visual feedback (closed-loop mode) and in darkness without visual feedback (open-loop mode). The patients had a tendency to generate abnormal saccades consisting of multiple small steps (multiple step saccade), both in the closed-loop and open-loop mode. They were, however, also capable of generating large amplitude saccades. The amplitude-velocity relation of both the small step saccades and the large saccades was normal. The presence of multiple step saccades in the open loop mode suggests that the patients used internal rather than external (visual) feedback to compare the actual eye position with the desired (programmed) eye position and the program for rapid movement is normal but its execution is defective. Horizontal eye movements were also recorded when the head was stationary with a target moving sinusoidally, and when the target was stationary with the head rotated sinusoidally. In both cases the amplitude of the eye movement relative to the head was about 50 degrees. The patients were observed to generate irregular, saccadic eye movements in pursuit of a slowly moving target when the head was stationary, but their eyes could follow a stationary target smoothly when their eyes could follow a stationary target smoothly when their head was moved sinusoidally. These findings suggest that the neuronal circuitry in the paramedian pontine reticular formation, responsible for the final integration of different types of eye movements, is physiologically normal in Parkinsonism.