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Research shows that sniffing causes oscillation activity in the olfactory bulb of the cortex, leading to piriform cortex stimulation. The amount of oxygen in the blood stream directly affects the degree of piriform response that sniffing achieves, according to nuclear magnetic resonance imaging experiments. The piriform cortex of the temporal lobe is one of the brain areas most affected by the sniffing response.

Olfaction is often referred to as a multidimensional sense. It is multidimensional in that approximately 1000 different receptor types, each tuned to particular odor aspects, together contribute to the olfactory percept. In humans, however, this percept is nearly unidimensional. Humans can detect and discriminate countless odorants, but can identify few by name. The one thing humans can and do invariably say about an odor is whether it is pleasant or not. We argue that this hedonic determination is the key function of olfaction. Thus, the boundaries of an odor object are determined by its pleasantness, which--unlike something material and more like an emotion--remains poorly delineated with words. [ABSTRACT FROM AUTHOR]

Background: Breathing patterns may inform on health. We note that the sites of earliest brain damage in Parkinson's disease (PD) house the neural pace-makers of respiration. We therefore hypothesized that ongoing long-term temporal dynamics of respiration may be altered in PD., Methods: We applied a wearable device that precisely logs nasal airflow over time in 28 PD patients (mostly H&Y stage-II) and 33 matched healthy controls. Each participant wore the device for 24 h of otherwise routine daily living., Results: We observe significantly altered temporal patterns of nasal airflow in PD, where inhalations are longer and less variable than in matched controls (mean PD = -1.22 ± 1.9 (combined respiratory features score), Control = 1.04 ± 2.16, Wilcoxon rank-sum test, z = -4.1, effect size Cliff's δ = -0.61, 95% confidence interval = -0.79 - (-0.34), P = 4.3 × 10 -5 ). The extent of alteration is such that using only 30 min of recording we detect PD at 87% accuracy (AUC = 0.85, 79% sensitivity (22 of 28), 94% specificity (31 of 33), z = 5.7, p = 3.5 × 10 -9 ), and also predict disease severity (correlation with UPDRS-Total score: r = 0.49; P = 0.008)., Conclusions: We conclude that breathing patterns are altered by H&Y stage-II in the disease cascade, and our methods may be further refined in the future to provide an indication with diagnostic and prognostic value., Competing Interests: Competing interests The authors declare the following competing interests: The Weizmann Institute of Science and the Tel Aviv Sourasky Medical Center are applying for patent authored by co-authors M.A.G., K.S., D.H., A.W., T.S., A.R., L.G., N.H., A.E., T.G., and N.S., for “classifying PD by nasal airflow”. K.S., D.H., A.W., and N.S. have applied for patent on the device used to measure nasal airflow (the Nasal Holter) and together with author L.P. have financial interests in a startup company developing this device. The startup company had no link to this study, and has no link or interests in PD., (© 2024. The Author(s).)

Olfaction may play a restricted role in human behavior, yet paradoxically, its absence in anosmia is associated with diverse deleterious outcomes, culminating in reduced life expectancy. The mammalian nose serves two purposes: olfaction and breathing. Because respiratory patterns are impacted by odors, we hypothesized that nasal respiratory airflow may be altered in anosmia. We apply a wearable device that precisely logs nasal airflow for 24-hour-long sessions in participants with isolated congenital anosmia and controls. We observe significantly altered patterns of respiratory nasal airflow in anosmia in wake and in sleep. These differences allow classification of anosmia at 83% accuracy using the respiratory trace alone. Patterns of respiratory airflow have pronounced impact on health, emotion and cognition. We therefore suggest that a portion of the deleterious outcomes associated with anosmia may be attributed to altered patterns of respiratory nasal airflow rather than a direct result of lost odor perception per se., (© 2024. The Author(s).)

An ongoing debate exists regarding the feasibility of placing self-expanding metallic stents (SEMS) within 5 cm of the anal verge. Traditionally, SEMS have been considered contraindicated for patients with a malignant rectal obstruction within this region due to potential impact on the anorectal ring or anal canal, which can cause incontinence, proctalgia, and tenesmus. However, in the case of a 63-year-old female who presented with distention, abdominal pain, and diminishing stool output, the rectal exam identified a bulky fixed mass. Imaging studies revealed large bowel obstruction and high-grade stricture, with a minuscule residual lumen. Endoscopy identified a bulky mass obscuring the lumen at 5 cm from the anal verge, and biopsy confirmed adenocarcinoma. Despite the traditionally held contraindication, a 2.5 cm × 9.0 cm colonic stent was successfully deployed, leading to brisk colonic decompression. This allowed the patient to promptly undergo chemoradiotherapy., Competing Interests: No conflicts of interest were reported., (Published by Oxford University Press and JSCR Publishing Ltd. © The Author(s) 2023.)

Terrestrial mammals identify conspecifics by body odor. Dogs can also identify humans by body odor, and in some instances, humans can identify other humans by body odor as well. Despite the potential for a powerful biometric tool, smell has not been systematically used for this purpose. A question arising in the application of smell to biometrics is which bodily odor source should we measure. Breath is an obvious candidate, but the associated humidity can challenge many sensing devices. The armpit is also a candidate source, but it is often doused in cosmetics. Here, we test the hypothesis that the ear may provide an effective source for odor-based biometrics. The inside of the ear has relatively constant humidity, cosmetics are not typically applied inside the ear, and critically, ears contain cerumen, a potent source of volatiles. We used an electronic nose to identify 12 individuals within and across days, using samples from the armpit, lower back, and ear. In an identification setting where chance was 8.33% (1 of 12), we found that we could identify a person by the smell of their ear within a day at up to ~87% accuracy (~10 of 12, binomial P < 10-5), and across days at up to ~22% accuracy (~3 of 12, binomial P < 0.012). We conclude that humans can indeed be identified from the smell of their ear, but the results did not imply a consistent advantage over other bodily odor sources., (© The Author(s) 2024. Published by Oxford University Press.)

Rodent tears contain social chemosignals with diverse effects, including blocking male aggression. Human tears also contain a chemosignal that lowers male testosterone, but its behavioral significance was unclear. Because reduced testosterone is associated with reduced aggression, we tested the hypothesis that human tears act like rodent tears to block male aggression. Using a standard behavioral paradigm, we found that sniffing emotional tears with no odor percept reduced human male aggression by 43.7%. To probe the peripheral brain substrates of this effect, we applied tears to 62 human olfactory receptors in vitro. We identified 4 receptors that responded in a dose-dependent manner to this stimulus. Finally, to probe the central brain substrates of this effect, we repeated the experiment concurrent with functional brain imaging. We found that sniffing tears increased functional connectivity between the neural substrates of olfaction and aggression, reducing overall levels of neural activity in the latter. Taken together, our results imply that like in rodents, a human tear-bound chemosignal lowers male aggression, a mechanism that likely relies on the structural and functional overlap in the brain substrates of olfaction and aggression. We suggest that tears are a mammalian-wide mechanism that provides a chemical blanket protecting against aggression., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Agron et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Nonhuman terrestrial mammals sniff themselves and each other to decide who is friend or foe. Humans also sniff themselves and each other, but the function of this is unknown. Because humans seek friends who are similar to themselves, we hypothesized that humans may smell themselves and others to subconsciously estimate body odor similarity, which, in turn, may promote friendship. To test this, we recruited nonromantic same-sex friend dyads and harvested their body odor. We found that objective ratings obtained with an electronic nose, and subjective ratings obtained from independent human smellers converged to suggest that friends smell more similar to each other than random dyads. Last, we recruited complete strangers, smelled them with an electronic nose, and engaged them in nonverbal same-sex dyadic interactions. We observed that dyads who smelled more similar had more positive dyadic interactions. In other words, we could predict social bonding with an electronic nose. We conclude that there is indeed chemistry in social chemistry.

In terrestrial mammals, body volatiles can effectively trigger or block conspecific aggression. Here, we tested whether hexadecanal (HEX), a human body volatile implicated as a mammalian-wide social chemosignal, affects human aggression. Using validated behavioral paradigms, we observed a marked dissociation: Sniffing HEX blocked aggression in men but triggered aggression in women. Next, using functional brain imaging, we uncovered a pattern of brain activity mirroring behavior: In both men and women, HEX increased activity in the left angular gyrus, an area implicated in perception of social cues. HEX then modulated functional connectivity between the angular gyrus and a brain network implicated in social appraisal (temporal pole) and aggressive execution (amygdala and orbitofrontal cortex) in a sex-dependent manner consistent with behavior: increasing connectivity in men but decreasing connectivity in women. These findings implicate sex-specific social chemosignaling at the mechanistic heart of human aggressive behavior.