Shared Functions of Perirhinal and Parahippocampal Cortices: Implications for Cognitive Aging

A predominant view of perirhinal cortex (PRC) and postrhinal/parahippocampal cortex (POR/PHC) function contends that these structures are tuned to represent objects and spatial information, respectively. However, known anatomical connectivity, together with recent electrophysiological, neuroimaging, and lesion data, indicate that both brain areas participate in spatial and nonspatial processing. Instead of content-based organization, the PRC and PHC/POR may participate in two computationally distinct cortical–hippocampal networks: one network that is tuned to process coarse information quickly, forming gist-like representations of scenes/environments, and a second network tuned to process information about the specific sensory details that are necessary for discrimination across sensory modalities. The available data suggest that the latter network may be more vulnerable in advanced age. Recent data do not support a content-based dissociation of PRC and PHC function. We propose a novel process-based model, rooted in anatomy, which contends that the PRC and PHC interact to support two distinct cortical–hippocampal pathways. One pathway through entorhinal cortex to the dentate gyrus and CA3 supports coarse processing of scenes and environments that quickly form gist-like representations for rapidly informing adaptive behavior. The other pathway is direct from PRC and PHC to CA1, and it enables detailed representations to be associated with gist-like information when a fine-grained analysis is necessary. Contemporary findings in cognitive aging studies in humans and other animals suggest that the PRC/PHC–hippocampal detail pathway is particularly vulnerable to the effects of aging.