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. We recently applied meta-analytic techniques to assess visual item recognition and location memory impairments that follow damage to the hippocampus and/or perirhinal cortex. Our meta-analysis indicated that impairments on tests of visual item recognition were larger after lesions of the perirhinal cortex than after lesions of the hippocampus. In addition, we found an influence of the task used to measure recognition memory. The visual paired comparison task (VPC), which infers object recognition from looking time, was found to be hippocampal dependent. By contrast, the delayed nonmatching-to-sample task (DNMS), which measures recognition through explicit choices, was relatively less hippocampal dependent. We hypothesized that VPC is not a pure measure of recognition memory. Instead, we propose that it reflects habituation and motivation, in addition to novelty preference. In humans, looking preferences can be independent of explicit recognition. Further, failure to show a looking preference cannot be interpreted as a lack of memory. We conclude that explicit tests of recognition memory (e.g., DNMS) should be given more weight than VPC in studies examining the neural bases of recognition memory.