The Hippocampal System and Relational (Declarative) Memory Processes

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DESCRIPTION (provided by applicant): The overall goal of the proposed research is to enhance our understanding of the relational nature of declarative memory, its dependence on the hippocampus and associated medial temporal-lobe (MTL) structures, and its role in supporting various aspects of human performance. The proposed work combines neuropsychological, eye movement, ERP, and fMRI studies, in a converging methods approach, to address a set of specific theory-driven claims and data-inspired questions about the nature, scope, and time course of relational memory processing. It also tests critical ideas about differential roles played by hippocampus vs other MTL memory structures. There are six specific aims: (1) To show that the hippocampus is centrally involved in relational memory binding of all manner of relations, including spatial, non-spatial co-occurrence, and temporal-sequential relations, above and beyond memory for the items themselves; (2) To show that although it plays a critical role in supporting conscious recollection and may participate in the detection or processing of novelty, the hippocampus supports relational memory, independent of conscious recollection, and even when item novelty is controlled for; (3) To show that the hippocampus is centrally involved in memory for relations among perceptually distinct objects, but not among features within objects; (4) To show that although it is involved in the formation of memory for all manner of relations, the hippocampus is necessary (only) for memory for arbitrary, accidental relations, not for non-arbitrary, derivable relations; (5) To show that the hippocampus is critical for relational memory even at the shortest lags or delays, i.e., even on the timescale of working memory; and (6) To examine the time course of aspects of relational memory processing. The memory system mediated by the hippocampus supports the particular form of memory that underlies remembering of the events and demands of everyday life, and, at the same time, the particular form of memory that is especially vulnerable to memory dysfunction in amnesia, in Alzheimer's disease, and even in the course of normal aging. Moreover, the hippocampus has been implicated not only in these instances of memory loss, but also in schizophrenia and depression. A better understanding of this critical system will have great significance.