Age-related changes in effects of monocular deprivation on cat striate cortex neurons

Publisher Website
Google Scholar
Abstract
Acute removal of the experienced eye in monocularly deprived cats produces a rapid increase in the percentage of striate cortex cells that respond to the deprived eye. The relationship of this phenomenon to the age of the animal was studied to assess the changes that occur in the functional inputs from the deprived eye to striate cortex, and in their interaction with inputs from the experienced eye, over the course of development with monocular deprivation. Kittens (32) were reared with monocular deprivation to ages ranging from 4-92 wk. For 20 animals, the experienced eye was enucleated and single-unit recording was carried out in striate cortex immediately afterward (group MD-DE-Immed). The remaining 12 animals served as monocularly deprived controls with no enucleation (group MD). Control experiments also were carried out following acute enucleation of 1 eye in a normal adult cat. In 4-5 wk old MD control kittens, the experienced eye drove 61-82% of the striate cortex cells, while the deprived eye drove only 0-15% of the cells. After acute enucleation of the experienced eye in 4-5 wk old MD-DE-Immed kittens, the deprived eye drove 59-74% of the cells. At 9-10 wk of age (near of the end of the critical period), the percentage of cells responsive to the deprived eye following enucleation decreased to between 7 and 21%. In 35-92 wk old Md-DE-Immed cats, 22-41% of the cells responded to the deprived eye after acute enucleation of the experienced eye. The increased responsiveness to the deprived eye was observed within the first 6 h of recording after the experienced eye was enucleated in MD-DE-Immed animals of all ages. With regard to visual-field eccentricity no differences were revealed in the effects of monocular deprivation, or in the effects of enucleating the experienced eye, for cells with central (0-4.degree.) vs. paracentral (4-10.degree.) receptive fields. Histological analysis showed that cells responsive to the deprived eye in MD-DE-Immed cats were present in all cortical layers, regardless of age. They tended to occur in clusters of responsive cells separated by runs of nonresponsive cells. The clusters of responsive cells are perhaps related to the ocular-dominance columns in striate cortex. At least 2 different mechanisms appear to underlie the effects of monocular deprivation in striate cortex: inhibition between inputs from the experienced and deprived eyes and subsequent loss of some of the inputs from the deprived eye. Although the outward effects of monocular deprivation appear the same at all ages studied, the relative contribution of these 2 mechanisms changes markedly with age.