XXIV Effects of Labyrinthectomy on Canal Sickness in Squirrel Monkey

Abstract

Six healthy squirrel monkeys, which readily developed canal sickness when exposed to slow rotation, were divided into two groups. One group was subjected to a unilateral left labyrinthectomy, the other group to a bilateral labyrinthectomy. Following surgery both groups of animals demonstrated evidence of vestibular dysfunction in unsteadiness of gait. This unbalance disappeared within six weeks following unilateral labyrinthectomy but persisted with gradual improvement in the bilateral labyrinthectomized animals. Following bilateral labyrinthectomy all three monkeys developed a complete insensitivity to canal sickness which remained throughout the four month period of observation. A similar lack of symptoms from rotation was seen initially in the three monkeys subjected to a unilateral labyrinthectomy; however, this behavior proved to be temporary, and by six months the animals had nearly returned to the pre-surgical level of sensitivity to canal sickness. Caloric tests done before and after surgery indicated complete loss of canal function in the operated ears; there was a slight rise in sensitivity in the non-operated ears.