Perirhinal cortex contributes to accuracy in recognition memory and perceptual discriminations.

The prevailing view of the medial temporal lobe (MTL) holds that its structures are dedicated to long-term declarative memory. Recent evidence challenges this position, suggesting that perirhinal cortex (PRc) in the MTL may also play a role in perceptual discriminations of stimuli with substantial visual feature overlap. Relevant neuropsychological findings in humans have been inconclusive, likely because studies have relied on patients with large and variable MTL lesions. Here, we conducted a functional magnetic resonance imaging study in healthy individuals to determine whether PRc shows a performance-related involvement in perceptual oddball judgments that is comparable to its established role in recognition memory. Morphed faces were selected as stimuli because of their large degree of feature overlap. All trials involved presentation of displays with three faces. The perceptual oddball task required identification of the face least similar to the other display members. The memory task involved forced-choice recognition of a previously studied face. When levels of behavioral performance were matched, we observed comparable levels of activation in right PRc for both tasks. Moreover, right PRc activity differentiated between accurate and inaccurate trials in both tasks. Together these results indicate that declarative memory demands are not a prerequisite for a performance-related engagement of PRc and that the introduction of such declarative memory demands in an otherwise closely matched perceptual task does not necessarily lead to an increase in PRc involvement. As such our findings show that declarative memory and perception are not as clearly separable at the level of MTL functioning as traditionally thought.