Abstract
SummaryMedial temporal lobe (MTL) structures including the hippocampus, entorhinal cortex, and perirhinal cortex are thought to be part of a unitary system dedicated to memory [1, 2], although recent studies suggest that at least one component—perirhinal cortex—might also contribute to perceptual processing [3–6]. To date, the strongest evidence for this comes from animal lesion studies [7–14]. In contrast, the findings from human patients with naturally occurring MTL lesions are less clear and suggest a possible functional difference between species [15–20]. Here, both these issues were addressed with functional neuroimaging in healthy volunteers performing a perceptual discrimination task originally developed for monkeys [7]. This revealed perirhinal activation when the task required the integration of visual features into a view-invariant representation but not when it could be accomplished on the basis of simple features (e.g., color and shape). This activation pattern matched lateral inferotemporal regions classically associated with visual processing but differed from entorhinal cortex associated with memory encoding. The results demonstrate a specific role for the perirhinal cortex in visual perception and establish a functional homology for perirhinal cortex between species, although we propose that in humans, the region contributes to a wider behavioral repertoire including mnemonic, perceptual, and linguistic processes.
Highlights
To investigate whether human perirhinal cortex contributes to perception in a manner homologous to that seen in macaques, we conducted a functional neuroimaging study with healthy volunteers performing a visual discrimination task used previously in both animal [7] and human patient studies [15, 16, 18]
Difficult feature trials could be performed on the basis of a single feature, whereas difficult objects required identifying that three different images represented a single object shown from different views
The critical distinction was that only the difficult object condition required objects to be identified at an abstract level and was expected to activate perirhinal cortex
Summary
Stimuli came from four different conditions drawn from a 2 3 2 factorial design that crossed the stimulus type (object versus feature) with the processing level (difficult versus easy). The critical distinction was that only the difficult object condition required objects to be identified at an abstract level and was expected to activate perirhinal cortex.
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