Recognition memory may be supported by two independent processes, conscious recollection of specific experiences and a sense of familiarity from prior exposure to stimuli. Observations on amnesic patients and functional imaging studies in humans suggest that the hippocampus may be critical to recollection whereas the parahippocampal region supports familiarity. However, these reports are controversial and definitive evidence is beyond the anatomical resolution of studies on humans. Recently, we adopted for studies on animals signal detection techniques originally developed to characterize these recognition processes in humans. Our results showed that recognition memory in rats is consistent with the dual process account and that recollection-like memory is dependent on the hippocampus. Here we propose to extend this animal model to characterize the fundamental nature of recollection and familiarity and to identify the functional circuitry that supports recognition memory. First, we will vary test task parameters to identify the cognitive processes that distinguish recollection and familiarity. These experiments will determine whether recollection-like memory in animals involves a slow, threshold retrieval of items and associated stimuli and context whereas familiarity-like memory involves a fast, continuous, perceptual matching to specific stimuli. Second, we will explore the role of brain structures implicated in recollection and familiarity, specifically subdivisions of the hippocampus, the parahippocampal region, and the prefrontal cortex. These experiments will test a working hypothesis about information processing steps within the cortical-hippocampal system. The combined studies will contribute to the development of animal models that are useful in the assessment of treatments for memory disorder.
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