Neural mechanisms underlying recognition memory

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The overarching goal of the proposed research is to understand how the brain supports memory. It is well-established that long-term memory relies on a set of heavily interconnected structures deep inside the brain that make up what is called the medial temporal lobe (MTL). Most memory researchers believe that these structures in the MTL form a system that is solely dedicated to long-term memory, meaning that these structures have no role in any other cognitive processes such as perception, attention, or working memory. This view is consistent with a popular paradigm in cognitive neuroscience, in which the brain is understood in terms of neatly segregated regions or cognitive modules that are each responsible for different broad psychological functions. Within this framework, it is argued that separate brain systems account for distinct cognitive processes, like “long-term memory,” “working memory,” or “perception.” The proposed research will suggest that this view is neither the most parsimonious nor the most compelling account of the data. Although it is clear that the structures in the MTL are essential for memory, recent findings indicate that these MTL structures do, in addition, play a critical role in perception – a finding that is fundamentally incompatible with the notion of a dedicated MTL memory system specifically, or cognitive modules more generally. In contrast to a modular view of memory, the proposed research will use neuropsychological and neuroimaging techniques to demonstrate that the functions of brain regions can be better understood in terms of the types of information they represent and the computations they perform. This research will suggest that the MTL should be considered as belonging to the ventral visual stream, a continuous hierarchy of regions that gradually increase in the complexity of information that they process. We propose that whereas regions lower down in the ventral visual stream are responsible for representing the simpler features that make up objects, the perirhinal cortex (PRC) – a key structure of what is currently thought to be the MTL memory system – sits at the peak of this ventral visual stream hierarchy. We argue that a critical function of the PRC is to represent the complex combinations of features that comprise whole objects, and will demonstrate that these complex “object-level” PRC representations are what allow us to make fine-grained distinctions between objects that have similar features. Importantly, we will show that the loss of this ability to discriminate between visually similar objects leads not to memory loss, as is commonly assumed, but rather to a paradoxical false memory for objects that were never seen before. This project stands to redefine current conceptions of memory by shifting the focus away from explaining functions in terms of specialized cognitive modules (e.g., for long-term memory or perception), and instead towards explaining cognitive processes in terms of how the underlying information is represented in the brain. In addition, through the use of convergent techniques – behavioural studies using modern cognitive paradigms and state-of-the-art neuroimaging – this project will provide exceptional research training opportunities that will strengthen Canada’s knowledge-based economy.