Prolonged sensitivity to monocular deprivation in dark-reared cats

Abstract

Starting just after birth, kittens were reared in total darkness until they were 4 mo. of age. They were then removed from the dark, and one eye was deprived of vision by suturing the eyelid shut. Subsequently the kittens were allowed varied periods of monocular vision (3 days to 2 mo.) in a normally lighted environment before recording. Recordings of single cells in the striate cortex of these kittens showed that visual stimulation through the nonsutured eye influenced many more cortical cells than did stimulation through the eye that had been deprived of vision. Recordings from control kittens that were reared in the light for 4 mo. and then subjected to 3 mo. of monocular eyelid suture showed that modification of cortical binocular connectivity was still possible in kittens of this age, but the effects of the eyelid suture were much less pronounced in light-reared cats than in the dark-reared cats of the same age. Additional kittens were maintained in the dark until they were 6, 8 or 10 mo. of age before one eyelid was sutured for a 3-mo. period. Irrespective of the kitten''s age, monocular deprivation caused a marked shift of the distribution of cortical ocular dominance in favor of the nonsutured eye. Cortical recordings from light-reared cats monocularly sutured at different ages indicated that the critical period for the effectiveness of monocular deprivation ends between 5 and 8 mo. rather than at 3 mo., as had been throught previously. Clear effects of monocular deprivation in previously dark-reared cats could be obtained after monocular exposures as short as 3 days. The strength of these effects reached asymptote with 2-4 wk of monocular vision. Immediately after dark rearing, most cortical units lack orientation selectively. The incidence of orientation-selective units rises rapidly in kittens allowed subsequent monocular visual exposure and reaches asymptote at near-normal levels after 2-4 wk. The incidence of orientation-selective units with strong influence from the deprived eye increases with increased duration of visual exposure for the nondeprived eye. The capacity for modification of cortical binocular connectivity apparently does not depend solely on the animal''s age. Depriving animals of visual experience before monocular deprivation is instituted appears to permit modification of cortical binocular connectivity irrespective of the animal''s age.