Smell perception plays an important role in eating behavior and might be involved in body weight gain. Since a body of literature implies that olfactory perception and function is hampered in obesity, we here investigate neuroanatomical correlates of this phenomenon. We assessed olfactory bulb (OB) volume with magnetic resonance imaging in 67 healthy participants with a body mass index (BMI) from 18.9 to 45.4 kg/m2 (mean = 28.58 ± 6.64). Moreover, we obtained psychophysiological data on olfactory ability (Sniffin’ Sticks, Food associated odor test) and self-report measurements on eating behavior. Additionally, we collected parameters associated with metabolic health in obesity (waist-hip ratio, waist-height ratio, leptin levels, body fat percentage, fat mass index, insulin resistance) to investigate recently proposed mechanistic explanatory models of why olfaction may be altered in obesity. We showed that OB volume was significantly lower in participants with obesity when compared to those of normal weight. Moreover, we found weak to moderate negative correlations between OB volume and BMI and related measures of metabolic health, especially leptin, body fat percentage, waist-height ratio and insulin resistance. However, neither OB volume nor BMI were related to olfactory function in our young and healthy sample. Nevertheless, our results provide first indications that obesity is associated with brain anatomical changes in the OBs.

Variability in human olfactory sensitivity has been attributed to individual-level factors such as genetics, age, sex, medical history of infections and trauma, neurogenerative diseases, and emotional disorders. Scarce evidence exists on the cross-cultural variation in olfactory sensitivity. Hence, we performed 2 studies to estimate the variability in olfactory threshold as a function of location and environment. Study 1 involved 11 laboratories from 4 continents (N ϭ 802). In each location, in a designated laboratory, approximately 80 subjects underwent olfactory sensitivity testing with custom-made tests with eucalyptol and phenylethanol (PEA) odors. Tests were based on the Threshold subtest of the Sniffin' Sticks battery.In Study 2, we compared olfactory sensitivity and suprathreshold perception of PEA and eucalyptol in 2 Chinese (N ϭ 160) and 2 Indian (N ϭ 92) populations-one based in their native country and the other in Germany. Both studies present large-scale evidence that olfactory sensitivity varies as a function of geographical location and suggest that environmental factors play an important role in shaping olfactory sensitivity and suprathreshold olfactory perception. We delineate further steps necessary to identify specific factors underlying uncovered variability and the relationship between olfactory sensitivity and suprathreshold odor perception.

Background- Nasal cycle (NC) is a rhythmic change of lateralized nasal airflow mediated by the autonomous nervous system. Previous studies reported the dependence of NC dominance on handedness and hemispheric cerebral activity. Objective- We aimed to investigate firstly, the possible lateralized effect of NC dominance on olfactory bulb volume: the first cerebral region processing olfactory information, and secondly, the association of NC dominance with the lateralized cerebral dominance in terms of olfactory processing. Methods- Thirty- five subjects (22 women, mean age 26 ± 3 years) participated in the study. NC dominance was ascertained using a portable rhino-flowmeter, the “Nasal Holter” for a duration of 24 h, out of which 22 subjects had right-dominant NC and 13 subjects had left-sided dominance. Structural and functional brain measurements were assessed using a 3T MR scanner (Siemens). Vanillin odor was presented during functional scans using a computer-controlled olfactometer. Results and Conclusions- NC dominance was found to be independent of the lateralization of olfactory bulb volumes. Also, cerebral activations were found independent of the NC during odor perception. NC dominance is not associated with lateralized structural or functional differences in the cerebral olfactory system.

No abstract