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

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Abstract
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) 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) in the closed- and open-loop mode. They were capable of generating large amplitude saccades. The amplitude-velocity relation of 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; the program for rapid movement is normal but its execution defective. Horizontal eye movements were 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 .apprx. 50.degree.. 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 head was moved sinusoidally. The neuronal circuitry in the paramedian pontine reticular formation, responsible for the final integration of different types of eye movements, is apparently physiologically normal in Parkinsonism.