ABSENCE OF RECOVERY OR DENDRITIC REORGANIZATION AFTER NEONATAL POSTERIOR PARIETAL LESIONS

Rats with bilateral removal of the posterior parietal cortex on Postna tal Day 5 or 10 were compared behaviorally and neuroanatomically to li ttermate control rats. The lesioned rats were impaired at the Morris w ater task but performed the Whishaw reaching task as well as control r ats. Although the lesioned rats learned to find the hidden platform ne arly as quickly as the control animals, their swim paths were less acc urate, reflecting a chronic deficit in orienting the body through spac e. In contrast to the effects of lesions in the frontal or occipital c ortex, posterior parietal lesions were not associated with compensator y dendritic growth in pyramidal cells in adjacent parietal cortex, a r esult that is consistent with an absence of functional recovery. Also in contrast to the effects of frontal lesions, there was no sex differ ence in the effects of posterior parietal lesions on either behavior o r dendritic arborization in nearby parietal cortex. These results impl y that the posterior parietal cortex is fundamentally different in its response to neonatal injury from other neocortical areas such as fron tal, motor, or occipital cortex.