Effects of visual deprivation and strabismus on the response of neurons in the visual cortex of the monkey, including studies on the striate and prestriate cortex in the normal animal

Abstract The response characteristics of neurons in the striate and prestriate cortex of normal macaque monkeys and those that had been raised under conditions of form deprivation or strabismus were studied with naturally presented visual stimuli. Most of these neurons were best activated by stimuli that had elongated borders of light and darkness which were moved through the receptive fields of the cells perpendicular to the long axis of the stimulus. The responses depended on the size, shape and orientation of the stimuli. In the normal animals most of the cells could be driven from either eye, although in the striate cortex 23% of the neurons were monocular, and in prestriate cortex there were 4% monocular cells. In both striate and prestriate cortex a small number of neurons did not respond to visual stimuli and others did not require an oriented-edge stimulus. Binocular stimulation of binocular cells revealed two classes of neurons. In the first class were those cells that gave a binocular response almost equivalent to the monocular response from the dominant eye and for which variation in the relative position (the ocular disparity) of the stimuli on the two retinas produced little change in the response. This type of neuron was seen in both striate and prestriate cortex. In the second class of binocular cell, seen only in prestriate cortex, the number of action potentials evoked by the stimuli depended on ocular disparity, and for a majority of these cells the response was markedly facilitated over a narrow range of disparities. The form deprived and strabismic animals had undergone eye surgery shortly after birth, producing monocular esotropia, exotropia or form deprivation by closure of the lid of one eye. The acuity in both eyes of each animal was tested during adult life. In general, the neurophysiological results demonstrated changes at the single neuron level which paralleled the degree of the behavioral changes: in animals with very poor acuity in the deprived or deviate eye (the form deprived and one esotropic animal), only a small number of neurons were driven from the operated eye; in one esotrope and the exotropic animal, which had good acuity in the operated eye, many neurons received an input from that eye, but only a small number of these were binocular. Finally, histological examination of the lateral geniculate nuclei of the form deprived animals revealed smaller, paler staining cells in those layers connected with the deprived eye.