The Critical Period for Corpus Callosum Section to Affect Cortical Binocularity

The period of time during which surgical section of the corpus callosum (CC) is effective in altering the physiological properties of cells in cat striate cortex was investigated. Cats which had the CC transected between 13 days and 24 weeks of age were studied using extracellular, single-unit recording procedures. Analysis of the results from 1,747 cortical units indicate that when the CC was sectioned prior to 19 days of age there was a reduction in the encounter rate of binocularly activated neurons and an increase in the proportion of neurons dominated by the contralateral eye. The decrease in cortical binocularity was observed in both simple and complex cell populations, and at all receptive field eccentricities studied (0-39 degrees). However, when the CC was sectioned after 19 postnatal days, no physiological changes were detected. Thus, in contrast with previous studies (Payne et al. 1980a, b) no changes were found following CC section in adult cats. The results therefore define a critical period which ends before 3 weeks of age during which corpus callosum section reduces striate cortex binocularity. Although the corpus callosum critical period is much shorter than the critical period for experiential alterations in cortical binocularity, the physiologically determined limits of the callosal critical period agree with the behaviorally determined limits previously found for the callosal critical period (Elberger 1984).