Nystagmus Induced by Electric Stimulation of Ampullary Nerves

Abstract

This investigation was supported by Research Grant NB-00294 from the National Institute of Neurological Diseases and Blindness. Dr. Suzuki was the recipient of a Fulbright Scholarship and was supported in part by grants from the Dazian and Abramson Foundations. We should like to acknowledge the help of Dr. Kazuyoshi Goto in one of the experiments presented, the technical assistance of Mr. Edward Murray, and helpful criticism of Drs. Julius Korein and Sidney Diamond during the course of this work.

Ampullary nerves were electrically stimulated with square waves in alert or lightly sleeping cats. This stimulus bypassed the ampullary receptor and permitted study of the response of the central vestibulo-oculomotor system to step increases in ampullary nerve frequency. In these animals such stimulation induced typical jerky nystagmus. The pattern of nystagmus was characteristic for each canal nerve stimulated. When two or more canals were simultaneously stimulated, the nystagmus from individual canals summated and nystagmus could be produced in any spatial plane. The electrically-induced nystagmus was recorded isometrically from eye muscles primarily activated by each canal. It was analyzed for amplitude, frequency, and velocity of the slow and fast phase muscle contractions. The sequence of changes in the slow phase contraction rate or amplitude of the nystagmus produced by a step increase in ampullary nerve frequency was similar to that of nystagmus produced by a step increase in angular acceleration. The electrically-induced nystagmus could also be summated with nystagmus induced by damaging the semicircular canals to slow, abolish or reverse it. Despite differences in the types of stimulation, nystagmus induced by electrical stimulation appears to qualitatively and quantitatively resemble nystagmus induced by angular acceleration or caloric stimulation.