Effect of vestibular deafferentation upon positional nystagmus in the squirrel monkey.
Seventeen of eighteen squirrel monkeys, under a restrained condition, showed positional nystagmus in different body positions. Good repeatability and consistency of the nystagmus were found, especially at the left-lateral, right-lateral, and head-hanging positions. Positional nystagmus was not observed after the subject underwent bilateral labyrinthectomy. However, one subject in which part of the crista ampullaris posterior remained, continuously showed a positional nystagmus. Therefore, the existence of a minimal vestibular imput from the crista ampullaris could provoke the nystagmus. Some changes occurred in positional nystagmus after bilateral macular ablation; however, the nystagmus did not completely disappear. Even though imput from the crista ampullaris is essential to provoke positional nystagmus in squirrel monkeys, the positional nystagmus probably results from a central dyscoordination between vestibulo-oculomotor function, spino-oculomotor function, vestibular and brain circulation, and psychological condition.
D000818:Animals; D003714:Denervation; D007758:Ear, Inner / Q000601:surgery; D005133:Eye Movements; D005260:Female; D000882:Haplorhini; D008297:Male; D011187:Posture; D012444:Saccule and Utricle / Q000502:physiology; D012453:Saimiri; D014722:Vestibule, Labyrinth / Q000502:physiology*