Recovery from early cortical lesions in rats. III. Neonatal removal of posterior parietal cortex has greater behavioral and anatomical effects than similar removals in adulthood.

The behavioral, anatomical, and electrophysiological effects of posterior parietal cortex lesions (Krieg's area 7) were compared in rats with removals at 1, 5, or 10 days of age or in adulthood. Behaviorally, the animals were administered several tests including grooming, beam walking, swimming, the Morris water task and a radial arm maze. Lesions at 10 days of age permitted behavioral sparing on most behavioral tasks, whereas lesions at 1 or 5 days of age allowed little sparing and even produced larger deficits than observed in adult operates on some tasks. Anatomical measures showed a direct relationship between cortical thickness and age of lesion: the earlier the lesion, the thinner the cortex. An analysis of postsurgical changes in cortical thickness showed only a small reduction in cortical thickness shortly after the lesions, with the major reduction occurring during adolescence. Electrophysiological recordings of cortical activity showed that rats with 1-day lesions had abnormal neocortical atropine-resistant activity and had an increased incidence of seizures. The results suggest that the neocortex of the rat may be particularly sensitive to perinatal injury.