A Contribution to the Mechanism of Vestibular Nystagmus: The Role of Afferent Impulses

Abstract

Lateral ampullary nerve and lateral ampulla were electrically stimulated with a single shock and repetitive shocks in anesthetized and unanesthetized cats with potentials in the vestibular and oculomotor nuclei were observed. The following results were obtained.

1. Evoked potentials recorded in the vestibular and oculomotor nuclei in response to the repetitive shocks differed remarkably from the potentials produced by a single shock. A characteristic negative wave, termed an M wave, was evoked concomitant with the slow phase of nystagmus only by repetitive shocks. With the administration of muscle relaxant the nystagmus and the M waves disappeared at the same time.

2. The possibility of afferent connections from the sensory endings in the extraocular muscles to the midbrain and the brain stem, was seriously considered.

3. It was reasonably interpreted that the accumulation of M waves in the central nervous system was an important factor, which also was coordinated through the neural regulation of the CNS to change the slow phase of nystagmus to the quick phase.