Factors Contributing to Labyrinthine Ataxia

Abstract

Twenty-one normal adults were the subjects of this study. They were instructed to step in the same position with eyes closed for a total of 50 steps under two conditions: i) Immediately after simultaneous irrigation of the right and left auditory canals for 10 s with 30°C water and 44°C water, respectively, and ii) following irrigation of the right auditory canal with 30°C water. The two conditions simulate two different types of imbalance of labyrinthine function: The former physiological and the latter non-phyiological. Under the first condition, 33% of the subjects tended to fall to the right side during stepping. Under the second conditions, 86% showed ataxia. The difference was statistically highly significant, p < 0.01. The results indicate that physiological imbalance does not always cause ataxia. A physiological imbalance occurs during active turning. The motion brings about an ampullopetal lymphatic flow in the ipsilateral horizontal semicircular canal and an ampullofugal flow in the contralateral canal, as under the second condition. The former increases the function of the labyrinth, while the latter decreases it. This results in imbalance but no ataxia.

Key Words:

• vestibulospinal reflex
• caloric stimulation
• semicircular canal