Structural changes in the visual cortex were studied in conditions of deranged binocular experience by assessing the sizes (body areas) of callosal cells in fields 17 and 18 in monocularly deprived cats and in cats with convergent strabismus. These cells were detected by injection of horseradish peroxidase into columns in cortical fields 17 and 18 and the fields 17/18 transitional zone. In both groups, the mean size of callosal cells in field 17 was greater than normal, though this difference in field 18 was seen only in monocularly deprived cats. Differences in the mean sizes of field 17 and 18 cells in cats of the study groups were found to be due to the number of large cells. In cats with strabismus, callosal cells of size greater than 200 μm2 accounted for 58% of cells in field 17 and 8% in field 18. In monocularly deprived cats, there was no difference in the proportions of large callosal cells in these fields (28% and 26%, respectively). These data provide evidence that cytoarchitectonic changes occurred in layers of the visual cortex, serving as sources of interhemisphere connections, in conditions of early derangement of binocular experience.
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