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Interactions between the hippocampus, prefrontal cortex and the ventral striatum during spatially-mediated foraging behaviour in the rat Floresco, Stanley Bogdan

Abstract

Numerous studies have implicated the hippocampus in spatial learning and memory. The present series of experiments assessed the role of the ventral CAl/subiculum (vCAl/sub) region of the rat hippocampus in performance of a spatially-mediated radial-arm maze test battery. The role of this structure during foraging was assessed when rats either had, or did not have previous information about the location of food. In addition, the present study investigated the interactions between the vCAl/sub and either the nucleus accumbens (N.Acc.) region of the ventral striatum or the prelimbic (PL) region of the medial prefrontal cortex during performance of these different radial-arm maze tasks. In Experiment 1, bilateral, transient, lidocaine-induced lesions of the vCAl/sub did not disrupt test-phase performance of a delayed spatial win-shift (SWSh) task, when lidocaine was administered prior to the training phase of this task. However, lidocaine infusions did impair foraging during the test phase of this task if lesions were administered prior to the test phase. Similarly, transient lesions of the vCAl/sub impaired performance during a random foraging (RF) task, which required rats to forage for four pellets placed randomly on an eight-arm maze. In Experiment 2, interactions between the vCAl/sub and either the PL or the N.Acc. were examined, using a "disconnection procedure", involving a unilateral lesion of the vCAl/sub and a contralateral lesion of the PL or the N.Acc. prior to either the delayed SWSh task or the RF task. Disconnections between the PL and the vCAl/sub did not disrupt foraging during the RF task, but severely disrupted foraging during the test phase of the delayed SWSh task. Conversely, disconnections between the N.Acc. and the vCAl/sub impaired foraging behavior on the RF task, but not the delayed SWSh task. The results of Experiment 1 suggest that the vCAl/sub region of the hippocampus is not involved in the acquisition of trial-unique spatial information, but is involved in the retrieval of this information following a delay. This region is also involved in foraging on a radial arm maze, in situations in which an animal has no prior information about the location of food in an environment. Furthermore, the results of Experiment 2 support the theory that as the demands of different foraging task vary, the hippocampus interacts with different forebrain structures to guide foraging behavior. During foraging when the animal has no prior information about the location of food, the vCAl/sub appears to interact primarily with the N.Acc. and not the PL to guide this behavior. During delayed foraging, the vCAl/sub interacts primarily with the PL but not the N.Acc. to guide behavior. The present results support the hypothesis that different neural circuits are involved in different types of foraging behavior.

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