Parietal cortex lesions do not impair retention performance of rats in a 14-unit T-maze unless hippocampal damage is present

Abstract

Young male F-344 rats, pretrained in a straight runway to avoid shock, were then trained in a shock-motivated 14-unit T-maze. One day after maze acquisition, extensive parietal cortex lesions (PC) or sham operations (CON) were performed to assess possible involvement of parietal cortex in the age-related impairment previously observed in this task. Twelve days after surgery, a first 10-trial retention session in the 14-unit T-maze was conducted. One day later the vibrissae of half the rats in each group were clipped to examine involvement of the damaged barrel cortex field in maze performance of rats with PC lesions. The following day a second 10-trial retention session occurred. Finally, retention of the straight runway avoidance response was tested. Histological verification revealed a group with consistent parietal damage but also a subgroup with relatively small lesions to dorsal or lateral hippocampus in addition to parietal damage (PC+HIP). Behavioral results revealed virtually perfect maze retention for CON and PC rats. In contrast, PC+HIP rats were severely impaired in maze retention performance. Retention of the straight runway avoidance response was perfect in CON and PC rats but was impaired in PC+HIP rats. Vibrissae clipping did not affect error performance in the maze but led to a transitory increase in runtime. Overall, the results indicate that parietal lobe damage shortly after acquisition does not impair retention performance of young rats in the 14-unit T-maze, unless hippocampal damage is also evident. Thus, parietal lobe dysfunction alone would not appear to be involved in the age-related retention impairment previously observed in this task.