The existence of a separate, brief critical period for the corpus callosum to affect visual development

The critical period for the role of the corpus callosum in visual development was explored in terms of the length of time during which the callosum has any influence on the development of visual acuity. Cats were given a surgical section of the posterior corpus callosum at 1, 2, 3, 4 and 29 weeks of age. These, as well as normal and operated control cats, were behaviorally tested for visual acuity thresholds from 5 through 29 weeks of age. Only the 1, 2 and 3 week callosum-sectioned cats showed deficits in visual acuity; the 4 and 29 week callosum-sectioned cats had acuity thresholds equivalent to those of the control cats. These results define a relatively brief critical period of time during which the corpus callosum effectively interacts with the developing visual system. This critical period ends during the fourth postnatal week; throughout the first postnatal month the corpus callosum's effectiveness in altering subsequent visual development gradually declines. Using the amount of acuity deficit as the measure of alteration of visual development, the input of the corpus callosum during the first postnatal month is as critical to visual development as is normal visual input during the first 4-6 postnatal months.