Neural Substrates of Stimulus Recognition and Association Memory

National Institute Of Mental Health

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Abstract

The hippocampus and perirhinal cortex are both broadly implicated in memory; nevertheless, their relative contributions to visual item recognition and location memory remain disputed. Neuropsychological studies that experimentally damage medial temporal lobe structures report various levels of memory impairmentranging from minor deficits to profound amnesia. The discrepancies in published findings have complicated efforts to determine the exact magnitude of visual item recognition and location memory impairments following damage to the hippocampus and/or perirhinal cortex. To provide the most accurate estimate to date of the overall effect size, we use meta-analytic techniques on data aggregated from 26 publications that assess visual item recognition and/or location memory in animals with and without selective neurotoxic lesions of the hippocampus or perirhinal cortex. We estimated the overall effect size, evaluated the relation between lesion extent and effect size, and investigated factors that may account for between-study variation. Grouping studies by lesion target and testing method, separate meta-analyses indicated that perirhinal cortex damage produced the largest impairment on tests of visual item recognition; by contrast, hippocampal damage produced the largest impairment on the subset of location memory tests that relied on spatial navigation. For the most part, meta-regressions indicated that greater impairment corresponds with greater lesion extent; paradoxically, however, hippocampal lesions predicted smaller impairments on tests of visual item recognition. We conclude the perirhinal cortex makes a larger contribution than the hippocampus to visual item recognition, and the hippocampus predominately contributes to spatial navigation.