Role of the neocortex in the water maze task in the rat: a detailed behavioral and Golgi-Cox analysis

The role of the neocortex in acquisition of the water maze task was investigated with both detailed behavioral and anatomical analyses. The neocortical areas examined were: (1) primary visual and posterior parietal areas Oc1 and Qc2M, (2) parietal area Par1, and (3) prefrontal areas Cg1, Cg3, IL, and part of Fr2 of Zilles, 1985. In Experiment 1, the effects of lesions in these areas were examined separately in different groups of naive male hooded rats. Additional rats were given water maze strategy pretraining before receiving a lesion, Strategy pretraining was used to separate water maze strategy learning from spatial learning to evaluate the contribution of the neocortical areas to these two components of task acquisition. All groups of naive lesioned rats were impaired in the task. In contrast, corresponding groups of pretrained lesioned rats performed as well as controls on all behavioral measures. In Experiment 2, the same neocortical areas lesioned in Experiment I were examined with the Golgi-Cox method to determine whether water maze training was associated with changes in the dendritic arborization of neocortical pyramidal cells. Contrary to expectations, no anatomical changes that could be ascribed to the behavioral training were seen in the areas and cortical layers examined. The data suggest that (1) these areas contribute to water maze strategy learning in naive rats, (2) none of the areas are crucially required for spatial learning provided rats are familiar with the general behavioral strategies required in the task before the lesion is made, and (3) any changes in neuronal morphology that occur as a consequence of the training may be subtle and widely distributed. (C) 2002 Elsevier Science B.V. All rights reserved.