Brainstem Commissures and Control of Time Constant of Vestibular Nystagmus

Abstract

Siir)itniin. Sagittal incision of the macaque brainstem near the midline and caudal and ventral to the abducens nuclei induces an oculomotor syndrome which includes reduction of the time constant of vestibular nystagmus. reduction in optokinetic after-nystagmus, polysaccadia. and sometimes impairment of gaze-holding and pursuit. In animals with effective lesions diazepam exerted its usual effect of increasing the time constant and decreasing the gain of vestibular nystagmus. These results suggest that inhibitory commissural fibers in the caudal brainstem influence the neural circuits that transform a short cupular time constant into a long nystagmus time constant.