Oculomotor function in the rhesus monkey after deafferentation of the extraocular muscles

The function of extraocular muscle proprioception in the control of eye mov ements remains uncertain. In this study, we examined the effect of bilatera l proprioceptive deafferentation of the extraocular muscles on eye movement s in two rhesus monkeys. Before and after deafferentation, we analyzed base line ocular alignment, saccades, pursuit, and vestibular eye movements. We also examined visually mediated adaptation of ocular alignment, saccades, a nd pursuit. Deafferentation of the eye muscles did not affect baseline ocul ar motor control, either acutely or over a 5-week period of study. Furtherm ore, visually mediated adaptation of the eye movement subtypes was also una ffected by deafferentation. These results suggest that ocular proprioceptio n in primates is not used in the immediate, on-line control of eye movement s and does not interact with visual cues in the adaptive modification of oc ular motor function. We conclude that the efferent command (efference copy) provides sufficient information about eye kinematics to the brain for accu rate eye movement control in normal monkeys, and that this information is m odified by visual feedback independently of proprioception. We hypothesize that proprioception may be used to calibrate the efference copy during deve lopment and in response to perturbations by signaling potential mismatches between eye movement information derived from the efferent command and the actual motion of the eye transduced by the proprioceptive organs.