The effects of hippocampal lesions on two neotic choice tasks

Abstract

We report two experiments in which rats with hippocampal lesions were tested in two neotic choice tasks that provided a clear distinction between novel and familiar alternatives. In the first experiment, rats with either dorsal or complete lesions were tested in an emergence task in which they were permitted to enter and explore a novel alley from a familiar nest box. Hippocampal animals did not differ from cortical controls on either the latency to enter the novel alley, the duration of time spent in the alley, or the total number of rearings in the alley during the 1 hour test. However, animals with complete hippocampal lesions were more active than cortical controls; they showed a perseverative tendency to repeatedly return to the familiar nest box. In the second experiment, rats with complete hippocampal lesions and cortical controls were tested in a two-bottle taste neophobia task using their familiar tap water and a novel saccharin solution. There were no differences between the groups in either the initial avoidance of the novel saccharin solution or the subsequent increase in saccharin preference across repeated tests. In both experiments, hippocampal animals showed the same initial neophobic avoidance followed by the same exploratory habituation as the cortical controls. We discuss the similarity of the hippocampal perseveration to behavior found in other exploratory tasks and conclude that the hippocampus is not essential for neotic information processing.