The role of the hippocampus in mnemonic integration and retrieval: complementary evidence from lesion and inactivation studies

Two forms of account have been proposed for how animals form integrated memories for patterns of stimulation: the elemental account holds that the elements that make up the pattern become directly linked to one another, whereas the configural account holds that these elements become bound together through their capacity to activate a separate, shared configural memory. The hippocampus and perirhinal cortex have been linked to both elemental and configural processes. Here, we assessed the role of the rat hippocampus and perirhinal cortex in these distinct ways of processing patterns of sensory stimulation involving auditory, visual context and temporal information. Using selective lesions and inactivation techniques we identified a specific role for the hippocampus in the retrieval of configural memories but not of those that could be encoded elementally; we also identified a role for the rat perirhinal cortex in visual contextual learning. These results, using a novel combination of behavioural assays, provide clear support for the view that patterns of stimulation can be encoded either elementally or configurally, and that disruption of hippocampal function leaves rats reliant on elemental processes.