Odors as Reactivation Cues During Sleep:  An Investigation of Memory Outcomes and Neural Mechanisms

Shanahan, Laura Kathleen

doi:https://doi.org/10.21985/n2-bvqt-ny34

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Odors as Reactivation Cues During Sleep: An Investigation of Memory Outcomes and Neural Mechanisms

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For years, neuroscientists have strived to understand memory consolidation, where salient memories are sorted and organized into distributed cortical networks for long-term storage. A large body of sleep research suggests that slow-wave sleep is an optimal opportunity for memory consolidation, and that consolidation is driven, at least in part, by a memory replay mechanism, where the same neural activity that occurs during memory encoding comes back online during sleep. Recently, scientists have demonstrated that sleep-borne sensory cues can be used to direct memory consolidation. Specifically, when memory encoding occurs in the presence of odor or sound cues, delivery of the same cues during subsequent sleep (i.e., reactivation) reinforces the associated memories, enhancing retrieval for those memories upon waking. Recent studies suggest that reactivation cues might promote consolidation by inducing replay of the associated material, but direct evidence for such mechanisms is scant, and the relevant brain regions supporting these processes are poorly understood. Here, we address these gaps by developing a novel olfactory reactivation paradigm, which included simultaneous EEG-fMRI recording in human subjects. We find that odor cues presented during sleep improved performance on an object-location memory task. Using multivariate pattern analysis of fMRI data, we also find that these memory gains are supported by neural replay of category-level information in ventromedial prefrontal cortex and visual associative cortex. In identifying the potential mechanisms by which odor cues selectively modulate memory consolidation, our findings bring unique insights into how memories are stored and preserved in the sleeping human brain.

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