Contribution of eye muscle proprioception to velocity-response characteristics of eye movements: involvement of the cerebellar flocculus.

The vestibulo-ocular reflex (VOR) and optokinetic nystagmus (OKN) were examined in alert pigmented rabbits following interruption of proprioceptive afferents from the extraocular muscles in one eye by surgical section of the ophthalmic branch of the trigeminal nerve (V1 nerve). Deficits were mainly produced in movement dynamics of the ipsilateral eye including reduction of (1) the VOR gain at a high frequency of head rotation, (2) the OKN gain and (3) the velocity of quick eye movements in the OKN. In some of the rabbits examined, the cerebellar flocculus was lesioned by local injection of kainic acid before severance of the V1 nerve. No significant additional reductions of VOR or OKN gains were produced by V1 nerve section in the flocculus-lesioned rabbits. These results suggest that proprioceptive signals from eye muscles act to improve VOR and OKN dynamics through the neuronal mechanisms involving the cerebellar flocculus.