Spatial deficits and hemispheric asymmetries in the rat following unilateral and bilateral lesions of posterior parietal or medial agranular cortex.

Studies of spatial behavior in both the human and non-human primate have generally focused on the role of the posterior parietal and prefrontal cortices and have indicated that destruction of these regions produce allocentric and egocentric deficits, respectively. The present study examined the role of the rodent analogs of these regions, the posterior parietal (PPC) and medial agranular (AGm) cortices, in egocentric and allocentric spatial processing, and whether spatial processing in rodents is organized in a hemispatial and/or lateralized manner as has been found in the primate. Eighty male rats receiving either a unilateral or bilateral lesion of AGm or PPC were examined on an egocentric (adjacent arm) or an allocentric (cheeseboard) maze task. The results indicated that PPC and AGm have dissociable spatial functions. Bilateral AGm destruction resulted in egocentric spatial deficits, and unilateral AGm operates demonstrated an intermediate deficit. In contrast, bilateral PPC operates demonstrated a severe deficit in allocentric processing. In addition, there were lateralized differences in the performance of unilateral PPC operates. While right PPC lesions resulted in a significant deficit on the allocentric task, no such deficit was seen in left PPC operates. In addition, neither unilateral AGm nor unilateral PPC operates demonstrated a hemispatial impairment on either the egocentric or allocentric tasks.