Static cervical-ocular reflex and optokinetic reflex interaction in rabbits

Summary The effect that tonic eye deviations, induced by angular deviation of the torso, have on the characteristics of optokinetic (OK) nystagmus was studied in rabbits. When the slow component of the OK nystagmus moved in the direction of the tonic eye deviation, the amplitude of the slow and fast components of the nystagmus was decreased and their frequency was increased, whereas when the slow component moved in the opposite direction, the amplitude and the frequency of the nystagmus were not different from those when the head and torso were aligned.Under the influence of neck reflexes, the total range of eye movements was double that when the torso was aligned with the head. The place in the orbit where the fast-component is initiated — the so-called fast-component threshold — was deviated in the direction of the neck-reflex-induced tonic eye deviation. The characteristics of the fast component, however, except for its amplitude, were not affected by the change of location of the fast-component threshold.These data indicate that the OK reflex function, as judged by measurement of the slow component velocity, is not affected by neck-vestibular reflexes. They also show that the fast-component threshold is dependent on parameters other than the actual orbital position and that there must be an internal representation of the range of possible eye movements within the brain to regulate the production of fast components.Abbreviations OK optokinetic - CW clockwise - CCW counterclockwise - CNS central nervous system This work was supported by grants NS07059, NS09823, and NS08335 from the National Institutes of Health