Dynamic Equilibrium in Squirrel Monkeys after Unilateral and Bilateral Labyrinthectomy

Abstract

The maintenance of dynamic equilibrium in the squirrel monkey, measured by squirrel monkey rail test, was investigated after unilateral, bilateral simultaneous, and bilateral non-simultaneous labyrinthectomy. After unilateral labyrinthectomy, most cases regained the pre-operative threshold level within 40–90 days postoperatively. After bilateral ablation of the peripheral labyrinth, whether simultaneous or not, the performance threshold of the squirrel monkey rail test severely declined. Therefore, it is concluded that the existence of peripheral vestibuIar labyrinth is essential for the maintenance of dynamic equilibrium when the condition requires advanced psychological and/or physical skill. Inasmuch as the dynamic balancing activity in daily life does not usually require advanced psycho-physical training and skill, the animals did not demonstrate any difficulty in their daily activities in the cages.