Highlights d How the human brain supports navigation in an odorous landscape is poorly understood d Subjects learn to orient within a 2D intensity space defined by two different odors d Odor navigation elicits grid-cell-like activity in prefrontal and entorhinal cortices d Findings suggest a mechanism by which the brain constructs olfactory cognitive maps

Slow-wave sleep is an optimal opportunity for memory consolidation: when encoding occurs in the presence of a sensory cue, delivery of that cue during sleep enhances retrieval of associated memories. Recent studies suggest that cues might promote consolidation by inducing neural reinstatement of cue-associated content during sleep, but direct evidence for such mechanisms is scant, and the relevant brain areas supporting these processes are poorly understood. Here, we address these gaps by combining a novel olfactory cueing paradigm with an object-location memory task and simultaneous EEG-fMRI recording in human subjects. Using pattern analysis of fMRI ensemble activity, we find that presentation of odor cues during sleep promotes reactivation of category-level information in ventromedial prefrontal cortex that significantly correlates with post-sleep memory performance. In identifying the potential mechanisms by which odor cues selectively modulate memory in the sleeping brain, these findings bring unique insights into elucidating how and what we remember.

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Growing evidence suggests that internal factors influence how we perceive the world. However, it remains unclear whether and how motivational states, such as hunger and satiety, regulate perceptual decision-making in the olfactory domain. Here, we developed a novel behavioral task involving mixtures of food and nonfood odors (i.e., cinnamon bun and cedar; pizza and pine) to assess olfactory perceptual decision-making in humans. Participants completed the task before and after eating a meal that matched one of the food odors, allowing us to compare perception of meal-matched and non-matched odors across fasted and sated states. We found that participants were less likely to perceive meal-matched, but not non-matched, odors as food dominant in the sated state. Moreover, functional magnetic resonance imaging (fMRI) data revealed neural changes that paralleled these behavioral effects. Namely, odor-evoked fMRI responses in olfactory/limbic brain regions were altered after the meal, such that neural patterns for meal-matched odor pairs were less discriminable and less food-like than their non-matched counterparts. Our findings demonstrate that olfactory perceptual decision-making is biased by motivational state in an odor-specific manner and highlight a potential brain mechanism underlying this adaptive behavior.

The olfactory system—and odor perception by extension—is susceptible to state-dependent influences. This review delves into human behavioral research in this area, and also touches on mechanistic evidence and examples from animal work. The review summarizes studies on the impact of satiety state on olfaction, highlighting the robust effects of food intake on the perceived pleasantness of food odors and olfactory decision-making. The impacts of other behavioral states on olfaction are also discussed. While research in this area is more limited, preliminary evidence suggests that odor perception is altered by circadian state, sleep deprivation, and mood. The flexibility in olfactory function described here can be considered adaptive, as it serves to direct behavior toward stimuli with high state-dependent value.