fNIRS neuroimaging in olfactory research: A systematic literature review.

There are a number of key features which make olfaction difficult to study; subjective processes of odor detection, discrimination and identification, and individualistic odor hedonic perception and associated odor memories. In this systematic review we explore the role functional near-infrared spectroscopy (fNIRS) has played in understanding olfactory perception in humans. fNIRS is an optical neuroimaging technique able to measure changes in brain hemodynamics and oxygenation related to neural electrical activity. Adhering to PRISMA guidelines, results of this search found that generally the majority of studies involving healthy adult subjects observed increased activity in response to odors. Other population types were also observed, such as infants, individuals with autism, attention deficit hyperactivity disorder (ADHD), post-traumatic stress disorder (PTSD), mild cognitive impairment (MCI) and dysosmia. fNIRS coverage heavily favored the prefrontal cortex, temporal and parietal regions. This review finds that odor induced cortical activation is dependent on multiple factors, such as odorant type, gender and population type. This review also finds that there is room for improvement in areas such as participant diversity, use of wearable fNIRS systems, physiological monitoring and multi-distance channels.

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Copyright © 2022 Gunasekara, Gaeta, Levy, Boot and Tachtsidis.

Déclaration de conflit d'intérêts

Author GG was employed by the company Givaudan; AL and EB were employed by the company Metabolight Ltd.; IT is full time employed at University College London, is the founder of Metabolight Ltd. and a consultant to Givaudan; NG is partially funded by EPSRC and Givaudan. The authors declare that this study received funding from Givaudan. The funder only had involvement during the conception of this literature review, and the decision to publish. The funder had no involvement during data collection, analysis, interpretation or the writing of this article. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.