Chapter 20 Visual and vestibular control of locomotion in early and late sensory-deprived cats

Abstract

This study focuses on how the vestibular system intervenes in the control of locomotion in the cat, and evaluates the impact of the visual environment on the development and recovery of vestibular functions. Bilateral destruction of the vestibular receptors was therefore combined with selective visual deprivation, both neonatally and in adult animals. The task was specially designed to investigate specific components of goal-directed locomotion, such as dynamic balance, keeping a straight course, and paw guidance during walking, depending on the characteristics of the walking surface. The main criterion of performance was the average walking speed of the animal when subjected to various visual conditions, including stroboscopic illumination. The effects of vestibular deprivation at an early age on locomotion control were found to be no more severe than those of later lesions, which indicates that early developmental processes involving vestibular information do not impinge on nonvestibular functions. As to the vestibular-related functions, they seem to partly develop in conjunction with kinetic visual cues. For instance, navigation in darkness is impaired in strobe-reared subjects. Furthermore, in adult cats, vestibular signals may be used in conjunction with visual reafferent information, since visual paw guidance is impaired in labyrinthectomized cats during walking. However, vestibular control is both necessary and sufficient for dynamic balance, in that it does not depend upon visual experience, and cannot be properly handled by the visual channel in either early or late vestibular-deprived cats. Impairment of this dynamic balance function may partly explain the deficits observed in other components of locomotor control, namely zigzaging or difficulties over irregular ground after labyrinthectomy. The main effect of age in labyrinthectomized cats is visual: in early vestibular-deprived animals, enhanced use is made of positional visual cues to control the direction of locomotion.