The effects of early visual experience followed by prolonged dark rearing on visual cortex cells of cats.

Five groups of kittens (N = 13) were dark reared for 9.5-20 months following normal binocular exposure of 0-85 days after natural eye opening and 1 month of monocular deprivation. For comparison, kittens monocularly deprived (MD) for 10 months (N = 2) and normal adult cats (N = 13) served as controls. The ocular dominance distribution of cortical cells showed a clear (although small) bias in the first group of kittens which received the minimal exposure. A striking effect was obtained in the proportion of visually unresponsive cells (55.1%) in this first group of cats. Concerning orientation and direction selectivity, the highest proportions of nonselective cells, 16.1% and 33.3%, were obtained in the first two groups of cats respectively. It was concluded that periods of monocular deprivation shorter than that used in the present study (4 weeks) and without any previous visual experience would be ineffective if followed by a year or more of total absence of visual experience. Prolonged dark rearing therefore, masks the effect of prior monocular deprivation to a large extent. In addition, the results emphasize the fact that the age factor is more important than the duration of the monocular visual experience.