Neural mechanisms of specificity and generalization learning

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Project summary Memory-based cognition depends on both the ability to remember specific details of individual experiences (specificity) and the ability to combine information across experiences to derive new knowledge (generalization). It is well established that the hippocampus rapidly encodes specific events, but the mechanisms of memory generalization are less clear. Traditionally, a division of labor has been postulated between the hippocampus, learning rapidly to support specificity, and other memory systems, learning slowly and incrementally to support generalization. More recent research has also shown a role of the hippocampus in rapid generalization, where new knowledge is derived by combining information across a small number of events. It is currently debated whether the hippocampal contribution to generalization is fully explainable by its role in storing specific experiences or whether the hippocampus integrates information across experiences to form generalized knowledge. Furthermore, it is unclear whether generalization learning proceeds at the expense of memory for specific details or whether multiple types of memory representations form and co-exist to serve multiple forms of cognition. The current project tests the hypotheses that representations at distinct levels of specificity form in parallel along the long axis of the hippocampus through interactions with distinct cortical regions. More anterior generalized representations inform generalization. More posterior specific representations support memory specificity but can also inform generalization decisions under circumstances when generalized representations have not been formed. To test these hypotheses, the proposed studies use functional MRI in humans during concept-learning tasks in which both specificity and generalization learning is indexed using (1) behavioral methods, (2) cognitive modeling and model-based fMRI, and (3) neural pattern similarity analyses. The studies will determine the mechanism(s) of memory generalization and how it relates to memory for specific events, the degree to which the formation of distinct representation is under strategic control, and the hippocampal-cortical interactions that contribute to specificity and generalization learning. The results will reveal whether specificity and generalization are two behavioral expressions supported by a single neural representation, a single neural system that can form different types of memory representations under different task demands, or distinct neural systems that form distinct representations. The results will inform current theories of memory function and help reconcile a decades-long debate regarding the nature of concept representations. The basic science knowledge obtained here will help shed light on the memory and generalization mechanisms that may go awry in many neuropsychiatric disorders.