Absence of recovery or dendritic reorganization after neonatal posterior parietal lesions

Abstract

Rats with bilateral removal of the posterior parietal cortex on Postnatal Day 5 or 10 were compared behaviorally and neuroanatomically to littermate control rats. The lesioned rats were impaired at the Morris water task but performed the Whishaw reaching task as well as control rats. Although the lesioned rats learned to find the hidden platform nearly as quickly as the control animals, their swim paths were less accurate, reflecting a chronic deficit in orienting the body through space. In contrast to the effects of lesions in the frontal or occipital cortex, posterior parietal lesions were not associated with compensatory dendritic growth in pyramidal cells in adjacent parietal cortex, a result that is consistent with an absence of functional recovery. Also in contrast to the effects of frontal lesions, there was no sex difference in the effects of posterior parietal lesions on either behavior or dendritic arborization in nearby parietal cortex. These results imply that the posterior parietal cortex is fundamentally different in its response to neonatal injury from other neocortical areas such as frontal, motor, or occipital cortex.