Recovery from early cortical damage in rats. IV. Effects of hemidecortication at 1, 5 or 10 days of age on cerebral anatomy and behavior.

Rats with complete removal of the neocortex of one hemisphere in adulthood (hemidecorticate) were compared behaviorally and anatomically with rats with similar removals at 1, 5, or 10 days of age. There was an unexpected relationship between cortical thickness in adulthood and age at surgery: the earlier the lesion the thicker the cortex. At the two extremes rats hemidecorticated in adulthood had a reduction of up to 10% in the contralateral hemisphere, rats with hemidecortications on the day of birth had cortex that was thicker than adult operates. Behaviorally, the animals were administered several tests including a spatial navigation task, tests of beam walking and swimming, tests of turning bias, and a measure of claw cutting. The main finding was that although the hemidecortication at all ages produced a reliable behavioral change on all measures, the neonatal hemidecorticates performed better than the adults. Further, the earlier the lesion, the better the animals performed. These results are contrasted with the effects of bilateral frontal or parietal neocortical removals in infancy where the earliest lesions have the most severe effect on cortical thickness and behavior. This comparison shows that unilaterality of brain damage is an important factor in predicting recovery or sparing of function from early lesions.