Plasticity in the Cat Visual System

Abstract

Behavioral and electrophysiological techniques have been used to study plasticity in the cat visual system both during and after the critical period for development of cortical binocularity. Both kittens reared with unilateral or bilateral eye rotation and adult cats given monocular rotations after the critical period showed good visuomotor adaptation to the rearranged visual information. All animals were able to learn a brightness discrimination. However, the three animals with monocular rotations of more than 120[degrees] were unable to learn oriented pattern discriminations although kittens raised with combined bilateral rotations of approximately 160[degrees] were able to learn even the most difficult orientation-discrimination. Apart from this there did not appear to be any significant correlation between rate of learning and angle of rotation. All animals who learned the pattern discriminations showed considerable, though incomplete interocular transfer as assessed by improvement in initial performance and by savings and errors to criterion with the second eye as compared with the first. Electrophysiological examination of area 17, in the kittens raised with monocular or binocular rotations, indicated the involvement of factors other than disparate visual input to the two retinas and asymmetrical eye movements per se in the breakdown of cortical binocularity seen in strabismic animals. Although most of the neuronal properties of area 17 were comparable to those reported previously for animals with unilateral rotations, some evidence for physiological adaptation to monocular and binocular rotation was seen in the corticotectal cells of layer V. A large proportion of the binocular corticotectal cells seen in animals with a total rotation angle of approximately 90 degrees in both experimental groups showed significant shifts in direction selectivity such that the optimal stimulus direction was very similar in both eyes. Plasticity of the visual cortex after the critical period was also examined electrophysiologically and it was found that the cortical effects of early monocular deprivation could be reversed when both the visual input to the brain and the extraocular afferents of the experienced eye were removed. After the combined treatments of pressure blinding and retrobulbar block of the normal eye approximately 50% of the units encountered could be shown to be influenced by the formerly deprived eye.