The effects of early visual experience on the cat's visual cortex and their possible explanation by Hebb synapses.

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Abstract
Kittens were dark-reared until 4-6 wk old, and then for another 4-7 wk with various combinations of cylindrical lenses, monocular occlusion, and normal vision. Single unit recordings from 816 neurons of the visual cortex (area 17) were obtained after the end of exposure. Clear-cut effects on the distributions of the neuron ocular dominance and orientation preference were found yielding close correlations with the rearing conditions. Most cortical neurons prefer vertical stimulus orientations when experience is restricted to vertical contours in both eyes. If the experienced orientations are different in the 2 eyes, each eye dominates over those neurons whose orientation preference corresponds to the orientation this eye has experienced. When 1 eye is covered while the other sees only contours of 1 orientation, the ocular dominance distribution of cortical neurons shows a bias towards the open eye. Neurons dominated by this eye prefer orientations corresponding to the experienced range. Neurons preferring other orientations are shared between both eyes. When vision is unimpaired in 1 eye and restricted to vertical contours in the other, binocularity is common among neurons preferring vertical orientations. Neurons with orientation preferences off the vertical are mainly monocular and dominated by the eye with unrestricted vision. When normal monocular vision of 1 eye precedes restricted monocular vision of the other eye, only a few binocular units are encountered. Reversal of the initial effects of monocular experience is found only in neurons preferring the orientation that has been experienced by the newly opened eye. The other neurons remain dominated by the originally open eye. Complementary distributions of orientation preferences are found for the 2 eyes. A good correlation was found between the amount of orientational experience as determined by the number of orientations exposed and the number of normally tuned neurons. Conversely, the number of neurons responding to all orientations decreases with increasing amount of experience. Between 24-32% of all units analyzed were unresponsive to light stimulation or did not show any preference for a particular stimulus orientation. In all but 1 paradigm the number of non-oriented or unresponsive neurons was smaller than the number to be expected if the bias in the orientation-distribution after selective experience solely resulted from selective deprivation of those neurons committed to non-experienced orientations. These quantitative considerations indicate that the role of visual experience is not only to maintain innate properties of cortical neurons, but also to specify innately unspecific neurons. A mechanism that could account for both roles of visual experience is the matching of patterns of afferent activity with post-synaptic response properties. This is similar to that postulated by Hebb for adaptive synaptic connections.