Characterizing the Roles of the Perirhinal and Entorhinal Cortices in Configural Object Processing Across the Lifespan

In our environment, we encounter hundreds of objects which vary in their shape, texture, and colour. Critical to our perception and recognition of these objects is the ability to bind the configural arrangement between their constituent features into mental representations. Representational-hierarchical accounts characterize the medial temporal lobes (MTL) by the content and complexity of the representations that its subregions support. Specifically, nonhuman and human lesion studies point to the perirhinal cortex (PRC) as the primary site supporting configural object representations. More recently, however, age-related atrophy of the adjacent anterolateral entorhinal cortex (alERC) was shown to predict impaired configural processing. Anatomical boundaries between the PRC and alERC vary between individuals, making attempts to characterize separable roles of these subregions difficult. In this thesis, I aimed to disentangle the roles of the PRC and alERC in complex object representations, by delineating the MTL with a manual segmentation approach motivated by nonhuman and human histological findings. A large sample of younger and older adults (N = 94) completed a configural processing task while undergoing structural and functional magnetic resonance imaging (fMRI). I began my investigation (Chapter 2) by showing that volumetric changes in the alERC across the lifespan are linked to eye movement patterns reflecting configural processing. In Chapter 3, I leveraged fMRI activation among healthy younger adults to demonstrate how the alERC supports the PRC in distinguishing novel from familiar configural objects. Unlike the posteromedial entorhinal cortex, the PRC and alERC were sensitive to configurally recombined objects compared to repeated ones and also predicted eye movements related to novelty detection. In Chapter 4, I extended these analyses to a sample of community-dwelling older adults and found a marked decline in PRC and alERC activation for novelty. Finally, in Chapter 5, I provided a comparison of Chapters 3 and 4 to directly examine functional activation for configural processing in an aging context. By characterizing the roles of the PRC and alERC in object representations across the lifespan, the results presented in this thesis further critical insights into the organization of the human MTL and provide important implications for our understanding of cognitive aging.

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