Odor exposure causes long-lasting effects on resting-state networks in the human brain

Abstract Most brain imaging studies on olfaction focus on short-term odorant stimuli, with few examining long-lasting odor exposure or its after-effects. This study utilized resting-state fMRI (rsfMRI) to investigate the effects of prolonged odorant exposure on brain activity and whether these effects persist post-exposure. Fourteen healthy females underwent two fMRI sessions on different days in a randomized order. Each session included rsfMRI scans before, during, and up to two hours after a 14-minute exposure to either lavender essential oil or a non-odorant control. Independent Component Analysis identified the salience network (SN) and default mode network (DMN) as the most consistent resting-state networks. A two-factorial ANOVA revealed significant time-varying interaction effects between SN and DMN. During odor exposure, functional connectivity (FC) within the SN increased, and a negative correlation with the DMN appeared, which intensified immediately after exposure. Two hours post-exposure, the FC between SN and DMN turned positive. These findings demonstrate that prolonged odorant exposure induces long-lasting brain effects detectable up to two hours afterward, suggesting new possibilities for exploring aromatherapy or odor exposure interventions on brain activity.