Central eye nystagmus in the split-brain guinea pig

Abstract

The purpose of the present investigation was to examine the effects of acute, midline, symmetrical splitting of different parts of the brain on eye nystagmus in the guinea pig. Nystagmus was elicited by electrical stimulation of the temporoparietal cortex or of the nystagmogenic corticofugal fibers in the superior colliculus, by thermal stimulation of the labyrinth. Midline, symmetrical division of the corpus callosum and diencephalon, of the mesencephalon, or of the rostral most part of the bulb just caudal to the abducent nuclei did not suppress the nystagmus. However, it was abolished by splitting the whole pontomesencephalic region or, more simply, the pons at the level of or just rostral to the abducent nuclei. In this instance labyrinthine or central stimulation could induce conjugate or monocular eye deviation only occasionally. In the guinea pigs with split mesencephalon, abnormalities of conjugate eye movements were observed during nystagmus, particularly when the vestibular nuclei were ablated together with the cerebellum. Thus, the central eye nystagmus was horizontal in one eye and vertical in the contralateral one; in other cases monocular or convergent nystagmus was noted.