Perirhinal cortex tracks degree of recent as well as cumulative lifetime experience with object concepts

Publication date: Available online 31 January 2017
Source:Cortex
Author(s): Devin Duke, Chris B. Martin, Ben Bowles, Ken McRae, Stefan Köhler
Evidence from numerous sources indicates that recognition of the prior occurrence of objects requires computations of perirhinal cortex (PrC) in the medial temporal lobe. Extant research has primarily probed recognition memory based on item exposure in a recent experimental study episode. Outside the laboratory, however, familiarity for objects typically accrues gradually with learning across many different episodic contexts, which can be distributed over a lifetime of experience. It is currently unknown whether PrC also tracks this cumulative lifetime experience with object concepts accrued outside the laboratory. To address this issue, we conducted an fMRI experiment in healthy individuals in which we compared judgments of the perceived lifetime familiarity with object concepts, a task that has previously been employed in many normative studies on concept knowledge, with frequency judgments for recent laboratory exposure in a study phase. Guided by neurophysiological data showing that neurons in primate PrC signal prior object exposure at multiple time scales, we predicted that PrC responses would track perceived prior experience in both types of judgments. Left perirhinal cortex and a number of cortical regions that are often co-activated as part of the default-mode network showed an increase in BOLD response in relation to increases in the perceived cumulative lifetime familiarity of object concepts. These regions included the left hippocampus, left mid-lateral temporal cortex, as well as anterior and posterior cortical midline structures. Critically, left PrC was found to be the only region that showed this response in combination with the typically observed decrease in signal for perceived recent exposure in the experimental study phase. These findings provide, to our knowledge, the first evidence tying signals in human PrC to variations in cumulative lifetime experience with object concepts. These results offer a new link between its role in recognition memory and a broader role in conceptual processing.



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