| Summary: | The hippocampus and the prefrontal cortex are two areas of the brain that are fundamental for a wide range of cognitive processes. Studies of both human patients who have incurred damage to these regions, and animals with circumscribed lesions, have led to a variety of theories concerning their contributions to cognitive behaviours. The hippocampus and the prefrontal cortex are connected anatomically, but the behavioural sequelae of experimental lesions have been shown to be dissociable. This thesis investigates the roles of the hippocampus and the prefrontal cortex in the rat, with a focus on delayed matching working memory tasks. Chapter 4 reports on a study which demonstrated a delay-dependent deficit on retention of delayed matching to position (DMTP) in the Skinner box following prefrontal lesions hippocampal lesions left performance intact. Neither lesion impaired the ability to switch between matching and non-matching rules. Chapter 5 describes an experiment which revealed that neither area was involved in postoperative acquisition of DMTP. Next, rats with lesions of the two main hippocampal pathways were assessed on retention of DMTP in Chapter 6. Lesions of the fornix revealed a delay-independent deficit, whereas entorhinal cortex lesions were without effect. Chapter 7 investigated recognition memory using a spontaneous novelty preference task. None of the lesions impaired performance on this task up to a 2 hour delay, however hippocampal lesions showed an impairment when a spatial component was included. Furthermore, there was a suggestion of both prefrontal and hippocampal involvement when memory for relative recency was assessed. Finally, Chapter 8 investigated a novel task in the Skinner box which combined both rules within one session. This task revealed a surprising pattern of results, with hippocampal lesions producing a dramatic impairment, whilst prefrontal lesions were without effect. Additionally, water maze data provided ample support for a hippocampal role in spatial memory.
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