Neural Correlates of Both Perception and Memory for Objects in the Rodent Perirhinal Cortex.

Despite its anatomical positioning as an interface between the perceptual and memory systems, the perirhinal cortex (PER) has long been considered dedicated for object recognition memory. Whether the PER is also involved in object perception has been intensely debated in recent studies, but physiological evidence has been lacking. We recorded single units from the PER while the rat made categorical responses immediately after sampling a visual object as the originally learned objects were ambiguously morphed to varying degrees. Some neurons in the PER  changed their firing rates monotonically following the gradual changes across the morphed objects as if they coded perceptual changes of the object stimuli. However, other neurons abruptly changed their firing rates according to the response categories associated with the morphed objects, seemingly responding to the learned relationships between the stimulus and its associated choice response. The gradual and abrupt changes in object-tuning properties were also found at the neural population level. Furthermore, the object-associated tuning characteristics of neurons in the PER were more readily observable in correct trials than in error trials. Our findings suggest that neurons in the PER represent perceptual details of an object in addition to its mnemonic identity.