VESTIBULAR COMPENSATION - ROLE OF VISUAL-MOTION CUES IN THE RECOVERY OF POSTURO-KINETIC FUNCTIONS IN THE CAT

Vision has long been recognized as a sensorimotor system which plays a major role in substitution for functional deficits induced by unilate ral or bilateral exclusion of primary vestibular afferents. Little is known, however, about the post-lesion influence of visual inputs on th e recovery of posture-kinetic balance in a situation where fine, well- coordinated locomotor adjustments are required. The present study was carried out in order to gain some insight into the role played by moti on vision in the restoration of fine posture-kinetic balance in adult cats subjected to unilateral vestibular neurectomy. Prior to the lesio n, 15 adult animals were trained to cross a beam rotating at various s peeds. Their best global balance performance (highest beam rotation sp eed that did not provoke falling) and their average locomotion speed w ere evaluated. After the lesion, the cats were separated into three gr oups: (1) five animals were placed in a normal environment (animal hou se) (NV cats); (2) four animals were exposed to stroboscopic illuminat ion which eliminated visual motion cues (SV cats) for 2 weeks followin g the lesion; and (3) three animals were placed in a normal environmen t and their training was interrupted for the same period as in the SV cats (NVI cats). The possible influence of the 2-week deprivation of v isual motion cues on posture-kinetic balance was also examined in thre e intact cats. The present behavioral study showed that: (1) early sen sory deprivation caused suspension of the posture-kinetic balance reco very process as long as it was maintained; (2) complete restoration of global balance capacities developed following the vestibular neurecto my after a significant delay in half of the SV cats; (3) the lack of m otion cues resulted in severe alterations of fine posture-kinetic bala nce (inappropriate dynamic motor adjustments and irregular locomotion speed regulation) in all SV cats; and (4) the visual deprivation induc ed a a-week delay in the restoration of fine locomotor balance. These findings provide evidence for a defect in the visual sensory substitut ion processes that normally take place within the first few weeks foll owing exclusion of primary vestibular afferents.