Olfactory spatial memory: a systematic review and meta-analysis

Abstract

The human sense of smell is extraordinarily sensitive, and some argue that a main purpose of olfaction is to localize food sources. Yet, little is known about human spatial memory for odors and the existing literature has never been systematically summarized. In this systematic review and meta-analysis, we evaluated the evidence regarding human abilities to memorize arrangements of objects or routes based on olfactory cues, and compared results to those of other senses. We followed the PRISMA guidelines, searching three databases (PubMed, WoS, Scopus). Using manual and automated (ASReview) screening methods, we identified 24 articles that complied with our inclusion criteria (e.g., olfactory spatial memory task, healthy human adults). Four key results emerged. First, odors can be used as landmarks in the formation of neuro-cognitive maps in both sensory and cognitive brain areas, providing a foundation for spatial memory and navigation abilities. Second, the human ability to memorize locations of odors, especially cues signaling high-calorie food, is indicative of its presumed evolutionary role in foraging. Third, odor-recognition and odor-context-place association might stem from overlapping memory processes. Fourth, olfactory targeted training enhances olfactory spatial memory and shows transfer to other modalities and cognitive domains. Seven articles that compared performances in olfactory versus visual spatial memory were eligible for meta-analysis. The analysis was carried out using the standardized mean difference (i.e., Glass's estimator) as the outcome measure. A random-effects model was fitted to the data. Results showed that olfactory spatial memory is less effective than visual memory ( mu (<^>) = -0.48, 95% CI [ - 0.77, - 0.19]). Notably, two studies exhibiting the largest differences between sensory modalities were either evaluated as of moderate quality or included older participants. Furthermore, all included studies varied in the methods and materials used. Thus, we suggest that addressing methodological variations across studies and investigating the neural mechanisms will be pivotal for further advancing this research field.