Recovery from early cortical damage in rats. IX. Differential behavioral and anatomical effects of temporal cortex lesions at different ages of neural maturation.

Rats were given lesions of the temporal association cortex on postnatal day 4 or 10, or in adulthood. Ninety days later they were trained on two visual tasks (visual-spatial navigation; horizontal-vertical stripes discrimination). Lesion animals were compared behaviorally and neuroanatomically to littermate sham control rats. The day 4 lesions produced a larger deficit in the navigation task than day 10 or adult lesions. There were no deficits in the discrimination task. Analysis of the brains showed that the day 4 lesions produced a smaller brain and thinner cortex than day 10 lesions. The day 10 lesions produced hypertrophy in the dendritic arborization of pyramidal cells in parietal cortex. The results are consistent with the general findings that perinatal cortical injury in rats produces more severe behavioral and morphological effects than similar lesions in the second week of life and that cortical lesions around day 10 lead to an increase in cortical synaptogenesis.