VISUAL PERFORMANCE IN BEHAVING CATS AFTER PRENATAL UNILATERAL ENUCLEATION

Prenatal unilateral enucleation in mammals causes an extensive anatomi cal reorganization of visual pathways. The remaining eye innervates th e entire extent of visual subcortical and cortical areas. Electrophysi ological recordings have shown that the retino-geniculate connections are retinotopically organized and geniculate neurones have normal rece ptive field properties. In area 17 all neurones respond to stimulation of the remaining eye and retinotopy, orientation columns, and directi on selectivity are maintained. The only detectable change is a reducti on in receptive field size. Are these changes reflected in the visual behavior? We studied visual performance in cats unilaterally enucleate d 3 weeks before birth (gestational age at enucleation, 39-42 days). W e tested behaviorally the development of visual acuity and, in the adu lt, the extension of the visual field and the contrast sensitivity. We found no difference between prenatal monocularly enucleated cats and controls in their ability to orient to targets in different positions of the visual field or in their visual acuity (at any age). The major difference between enucleated and control animals was in contrast sens itivity: prenatal enucleated cats present a loss in sensitivity for gr atings of low spatial frequency (below 0.5 cycle per degree) as well a s a slight increase in sensitivity at middle frequencies. We conclude that prenatal unilateral enucleation causes a selective change in the spatial performance of the remaining eye. We suggest that this change is the result of a reduction in the number of neurones with large rece ptive fields, possibly due to a severe impairment of the Y system.