Pursuit eye movements and their neural control in the monkey

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Abstract
Single units in the 3. and 6. nerve nuclei were recorded, together with the stimulus and eye movements in trained macaques during pursuit eye movements. The relationship between the impulse rate of an oculomotor motoneuron and the corresponding eye movements can be described by a first order differential equation only, if distinctions are made between the modes of the oculomotor system (e.g., fixation or pursuit) and between the agonist phase and the antagonist phase of the corresponding eye muscle. The trained monkeys showed a frequency response during pursuit eye movements, which was comparable to that of humans and which clearly indicates the existence of a predictor mechanism. After sudden stimulus disappearance in the pursuit mode, both the neural impulse rate and the eye movement performed smooth changes for more than 1s. These slow post-pursuit eye movements were related to the time course before stimulus disappearance. Our findings lead to the hypothesis, that pursuit eye movements in primates, if elicited by small moving visual stimuli, are generated by means of a feedback system consisting of apredictor mechanism, the parameters of which are continuously corrected by anupdating process in the afferent visual system.