Menstrual cycle-modulated intrinsic connectivity enhances olfactory performance during periovulatory period*

Background: Olfactory capacity increases during the period of ovulation, perhaps as an adjunct to mate selection; however, researchers have yet to elucidate the neural underpinning of menstrual cycle-dependent variations in olfactory performance. Methodology: A cohort of healthy volunteers (n = 88, grand cohort) underwent testing for gonadal hormone levels and resting-state functional magnetic resonance imaging with a focus on intrinsic functional connectivity (FC) in the olfactory network based on a priori seeds (piriform cortex and orbitofrontal cortex) during the periovulatory (POV) and menstrual (MEN) phases. A subcohort (n = 20, olfaction cohort) returned to the lab to undergo testing of olfactory performance during the POV and MEN phases of a subsequent menstrual cycle. Results: Olfactory performance and FC were both stronger in the periovulatory phase than in the menstrual phase. Enhanced FC was observed in the network targeting the cerebellum in both the grand and olfaction cohorts, while enhanced FC was observed in the middle temporal gyrus, lingual gyrus, dorsal medial prefrontal cortex, and postcentral gyrus in the grand cohort. Periovulatory progesterone levels in the grand cohort were positively correlated with FC in the network targeting the insula and paracentral lobule. Conclusions: Our analysis revealed that superior olfactory function in the periovulatory period is associated with enhanced intrinsic connectivity in the olfactory network. These findings can be appreciated in the context of evolutionary biology.