California Institute of Technology

Changes in Functional Coupling Across Aging Memory Circuits

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Memory disorders disproportionately affect the aging population. The circuit-level mechanisms underlying these disorders remain poorly understood, hindering the search for effective cures. The hippocampus is a brain area critical for the formation but not the final storage of memories. The current predominant hypothesis is that memories are gradually established across cortical areas under the influence of the hippocampus. A well-documented feature of the hippocampus is its spatial map of the environment, where individual cells respond selectively when the animal is at a specific location in the environment. We aim to understand how the transfer of memories from the hippocampus to cortex takes place, and how aging affects this process as well as the hippocampal spatial maps. To address these questions, we are recording from hippocampal and cortical areas in both young and old animals as they learn a variety of spatial and non-spatial (simple association) learning tasks. As part of a collaborative study in young animals, we demonstrated that the dorsal hippocampus reports only spatial information, even in a non-spatial learning task. Since the hippocampus is necessary for learning this task, we hypothesize that the brain uses spatial information even for learning non-spatial tasks. This conjecture has interesting and testable implications for how learning is affected by aging, when spatial maps become unstable. We are studying how instability in hippocampal spatial maps correlates with inability to learn non spatial tasks in aged animals, and how memory transfer to cortical areas is affected as a result.