The role of the medial temporal lobe in discriminating complex object and scene stimuli

The emergent memory account (EMA) proposes that the medial temporal lobe (MTL), a region implicated in declarative memory, supports perception. EMA hypothesises that the perirhinal cortex (PRC) and hippocampus (HC), form complex conjunctions of objects and scenes, respectively, which can support fine-grained perceptual discriminations. This thesis combined both neuropsychological and functional imaging approaches, to examine the representations supported by the MTL. The final experiment applied one of the tasks in cognitive-genetic neuroimaging of Alzheimer‟s disease (AD). Consistent with EMA, patients with focal HC damage showed impaired learning of spatial, but not object, conjunctions (Chapter 2), and showed specific deficits in scene perception (Chapter 3). A complementary functional imaging study examined contributions of PRC and HC to the detection of object and scene differences, respectively; the predicted effects – PRC activation for object discrimination; HC for scene discrimination – were evident only at a relaxed statistical threshold. Significant MTL effects were demonstrated using an oddity task with items presented from different views (Chapter 4). Increasing object and scene feature overlap, however, did not increase PRC and HC activity; the opposite pattern was evident for scenes, with a novel context by feature overlap interaction for objects. In the final experimental Chapter (Chapter 5), it was found that young healthy adults at increased genetic risk of AD (ApoE-e4 carriers) showed increased scene-related activity in posterior cingulate cortex (PCC); a region affected, structurally, early in AD. The novel contributions of these findings are detailed in the General Discussion (Chapter 6). Briefly, they partially confirm EMA‟s predictions that the HC is necessary for learning conjunctive scenes, and that MTL involvement fractionates according to the stimulus to-be-processed. It also describes limitations of the experiments, proposes future challenges for representational accounts, and outlines experiments to elucidate the effect of ApoE-e4 on scene-related activity in PCC