Development of vertical vestibulo-ocular reflex characteristics in intact and flocculectomized rabbits visually deprived from birth.

The vertical vestibulo-ocular reflex (VOR) was recorded in dark-reared rabbits 3 months of age submitted in the dark to lateral sinusoidal oscillations of different frequencies and fixed amplitude. While the phase of the response was perfectly adequate to ensure head movements compensation, the gain values recorded showed a clear reduction with respect to the values obtained in a normally raised control group of the same age. After exposure to light, the visually deprived animals showed a complete and rapid recovery of normal VOR gain values. Another group of animals was flocculectomized prior to light exposure. The bilateral ablation of flocculus and paraflocculus did not affect the VOR characteristics of the deprived animals. After exposure to light, in the flocculectomized animals, no recovery of the VOR gain values was observed. The present results confirm that visual experience in early life is necessary for a correct development of the VOR. If visual deprivation is limited to the first few months of life, the impairment of the reflex characteristics is completely reversible. Finally our data suggest that in the rabbit, the flocculus controls the early life development of the VOR.