Olfactory Ability Research Articles

Temperamental Influences on Children’s Olfactory Performance: the Role of Self-Regulation

A body of research predominantly in young adults has suggested a link between olfactory perception, especially sensitivity, and personality characteristics, particularly neuroticism. Nevertheless, it is not clear whether these associations are present outside this particular age range and whether they involve other olfactory abilities, such as odor identification and discrimination, and temperamental differences in reactivity and self-regulation. On the one hand, extrapolating from studies with adults to children, participants scoring high on negative affectivity, which broadly maps onto neuroticism, should outperform the low-scoring ones. On the other hand, well-developed self-regulatory processes, referred to as effortful control, which modulate the expression of such tendencies, might also contribute to better olfactory performance. Thus, the aim of the present study was to investigate the effect of the temperamental factors on olfactory performance. Namely, we hypothesized that superior olfactory performance would be delivered by children scoring relatively higher on negative affectivity but also by those perceived as exhibiting greater self-regulation. Odor identification and discrimination in 143 children (72 boys) aged 6 to 8 years were assessed with the Sniffin‘ Sticks, controlling for verbal fluency. Parents provided reports of their children‘s temperament by means of a short form of the Children‘s Behavior Questionnaire. The potential influence of parental responsiveness and demands on temperamental attributions was controlled for with hypothetical vignettes representing parenting styles. There was an effect of effortful control (but not negative affectivity) on the total identification (but not discrimination) scores. Namely, children who were perceived as more capable of self-regulation exhibited higher odor identification scores. Girls did not outperform boys on either of the olfactory tests, but they were deemed by their parents to show greater self-regulation. Our findings indirectly point to the effect of self-regulatory tendencies on odor identification in young children. However, they did not corroborate the idea that children varying in negative affectivity (underlying neuroticism) differ in terms of olfactory performance. Given the narrow age range of children recruited in the present study, further studies with preadolescent and adolescent participants are needed to gain more insight into the nature of these relationships.

Self-Ratings of Olfactory Performance and Odor Annoyance Are Associated With the Affective Impact of Odor, but Not With Smell Test Results.

Our aim was to explore factors potentially associated with subjective (self-rated) and objective (measured using the Sniffin' Sticks Extended test) olfactory performance in the general population without olfactory disorders. We studied associations between olfactory performance and how important odors were in determining liking for new places, things, and people (measured using the Affective Impact of Odor scale) and the average annoyance caused by odors in 117 adults (83 women, 34 men; age 18-69 years, mean age 32 years). In a subset of 44 participants, we also studied associations between olfactory performance and spice odor identification task scores (14 odors) and the number of herbs and spices consumed. Self-rated olfactory acuity and odor-related annoyance were associated with the Affective Impact of Odor scores, but neither correlated with the smell test results. Instead, the number of spices consumed correlated with spice odor identification score ( r = .50) and the identification (but not threshold nor discrimination) subscore of the Sniffin' Sticks test ( r = .49). Our results suggest that a tendency to perceive odors in affective terms may be associated with overestimation of olfactory abilities and that recurrent exposure to a large variety of spice odors may improve performance on odor identification.

High Fructose Diet inducing diabetes rapidly impacts olfactory epithelium and behavior in mice.

Type 2 Diabetes (T2D), a major public health issue reaching worldwide epidemic, has been correlated with lower olfactory abilities in humans. As olfaction represents a major component of feeding behavior, its alteration may have drastic consequences on feeding behaviors that may in turn aggravates T2D. In order to decipher the impact of T2D on the olfactory epithelium, we fed mice with a high fructose diet (HFruD) inducing early diabetic state in 4 to 8 weeks. After only 4 weeks of this diet, mice exhibited a dramatic decrease in olfactory behavioral capacities. Consistently, this decline in olfactory behavior was correlated to decreased electrophysiological responses of olfactory neurons recorded as a population and individually. Our results demonstrate that, in rodents, olfaction is modified by HFruD-induced diabetes. Functional, anatomical and behavioral changes occurred in the olfactory system at a very early stage of the disease.

Multi-locus phylogenetic inference among New World Vultures (Aves: Cathartidae)

New World Vultures are large-bodied carrion feeding birds in the family Cathartidae, currently consisting of seven species from five genera with geographic distributions in North and South America. No study to date has included all cathartid species in a single phylogenetic analysis. In this study, we investigated the phylogenetic relationships among all cathartid species using five nuclear (nuc; 4060bp) and two mitochondrial (mt; 2165bp) DNA loci with fossil calibrated gene tree (27 outgroup taxa) and coalescent-based species tree (2 outgroup taxa) analyses. We also included an additional four nuclear loci (2578bp) for the species tree analysis to explore changes in nodal support values. Although the stem lineage is inferred to have originated ∼69 million years ago (Ma; 74.5–64.9 credible interval), a more recent basal split within Cathartidae was recovered at ∼14Ma (17.1–11.1 credible interval). Two primary clades were identified: (1) Black Vulture (Coragyps atratus) together with the three Cathartes species (Lesser C. burrovianus and Greater C. melambrotus Yellow-headed Vultures, and Turkey Vulture C. aura), and (2) King Vulture (Sarcoramphus papa), California (Gymnogyps californianus) and Andean (Vultur gryphus) Condors. Support for taxon relationships within the two basal clades were inconsistent between analyses with the exception of Black Vulture sister to a monophyletic Cathartes clade. Increased support for a yellow-headed vulture clade was recovered in the species tree analysis using the four additional nuclear loci. Overall, these results are in agreement with cathartid life history (e.g. olfaction ability and behavior) and contrasting habitat affinities among sister taxa with overlapping geographic distributions. More research is needed using additional molecular loci to further resolve the phylogenetic relationships within the two basal cathartid clades, as speciation appeared to have occurred in a relatively short period of time.

Cortical Plasticity and Olfactory Function in Early Blindness.

Over the last decade, functional brain imaging has provided insight to the maturation processes and has helped elucidate the pathophysiological mechanisms involved in brain plasticity in the absence of vision. In case of congenital blindness, drastic changes occur within the deafferented “visual” cortex that starts receiving and processing non visual inputs, including olfactory stimuli. This functional reorganization of the occipital cortex gives rise to compensatory perceptual and cognitive mechanisms that help blind persons achieve perceptual tasks, leading to superior olfactory abilities in these subjects. This view receives support from psychophysical testing, volumetric measurements and functional brain imaging studies in humans, which are presented here.

Changes in Olfactory discrimination associated to environmental Manganese in Adolescents

Introduction: Olfactory changes are frequently shown in Parkinsonian patients and may be related to dysregulation of Dopaminergic control. While studies have suggested that exposure to manganese (Mn) may be associated with Parkinsonism, there is limited information on Mn exposures and the olfactory function in children. Methods: We measured soil and house dust Mn levels in the household of 389 children in Brescia, Italy. Surface soil was assessed with a Niton pXRF instrument and dust samples were collected by sweeping a measured area with a plastic brush, or using a cyclone vacuum. Mn was determined with ICP-OES. To assess odor identification we used Sniffin’ Sticks-Olfactory Screening 12 test (Burghart Medical Technology). We examined the relationships of soil and indoor-outdoor dust Mn (log-transformed) with olfactory discrimination (log-odds of correct identification) using generalized linear models and generalized additive models, adjusting for age, sex, socioeconomic status index, mother education, smoking and drinking. We also tested the effect of environmental Mn using a generalized linear mixed effects model, that allowed us to estimate the difficulty associated with recognizing each of the 12 odors, taking into account the olfactory ability of each subject Results: We found that soil Mn (estimate=-0.125, p=0.02) indoor dust (-0.06, p=0.045) and outdoor dust Mn (estimate=-0.07, p=0.03) were associated with decreased odds of correct odor identifications. This effect was particularly evident in boys. Cloves (when compared with peppermint) was the most difficult odor to be recognized by boys and girls. Conclusions: Our findings suggest that higher environmental Mn levels measured in household dust, outdoor dust and soil may be associated with worse odor identification. These data support the potential influence of Mn on dopaminergic control of olfactory functions that may represent an early sign of neurotoxicity.

Olfactory Performance in a Large Sample of Early-Blind and Late-Blind Individuals.

Previous examinations of olfactory sensitivity in blind people have produced contradictory findings. Thus, whether visual impairment is associated with increased olfactory abilities is unclear. In the present investigation, I aimed to resolve the existing questions via a relatively large-scale study comprising early-blind (N = 43), and late-blind (N = 41) and sighted (N = 84) individuals matched in terms of gender and age. To compare the results with those of previous studies, I combined data from a free odor identification test, extensive psychophysical testing (Sniffin' Sticks test), and self-assessed olfactory performance. The analyses revealed no significant effects of sight on olfactory threshold, odor discrimination, cued identification, or free identification scores; neither was the performance of the early-blind and late-blind participants significantly different. Additionally, the self-assessed olfactory abilities of the blind people were no different than those of the sighted people. These results suggest that sensory compensation in visually impaired is not pronounced with regards to olfactory abilities as measured by standardized smell tests.

Estradiol-induced neurogenesis in the female accessory olfactory bulb is required for the learning of the male odor.

Odors processed by the main and accessory olfactory bulbs (MOB, AOB) are important for sexual behavior. Interestingly, both structures continue to receive new neurons during adulthood. A role for olfactory neurogenesis in sexual behavior in female mice has recently been shown and gonadal hormones such as estradiol can modulate adult neurogenesis. Therefore, we wanted to determine the role of estradiol in learning the odors of sexual partners and in the adult neurogenesis of female aromatase knockout mice (ArKO), unable to produce estradiol. Female wild-type (WT) and ArKO mice were exposed to male odors during 7days, and olfactory preferences, cell proliferation, cell survival and functional involvement of newborn neurons were analyzed, using BrdU injections, in combination with a marker of cell activation (Zif268) and neuronal fate (doublecortin, NeuN). Behavioral tasks indicated that both WT and ArKO females were able to discriminate between the odors of two different males, but ArKO mice failed to learn the familiar male odor. Proliferation of newborn cells was reduced in ArKO mice only in the dentate gyrus of the hippocampus. Olfactory exposure decreased cell survival in the AOB in WT females, suggesting a role for estradiol in a structure involved in sexual behavior. Finally, newborn neurons do not seem to be functionally involved in the AOB of ArKO mice compared with WT, when females were exposed to the odor of a familiar male, suggesting that estradiol-induced neurogenesis in the AOB is required for the learning of the male odor in female mice. Aromatase knockout mice (ArKO) presented deficits in olfactory preferences without affecting their olfactory discrimination abilities, and showed no functional involvement of newborn neurons in the accessory olfactory bulb (AOB) in response to the odor of a familiar male. These results suggest that estradiol-induced neurogenesis in the female AOB is required for the learning of the male odor.

Investigating Left- and Right-Nostril Olfactory Abilities with Respect to Psychopathy

Introduction Evidence for olfactory lateralization is mixed, although a left-sided benefit for odor identification seems likely. Whether lateralization of function is moderated by variables such as gender and handedness has been previously explored. However, there has been no test of whether psychopathy and empathy—personality characteristics which may themselves affect lateralization and which can affect olfactory function—moderate olfactory lateralization.

Developmental Changes in Adolescents' Olfactory Performance and Significance of Olfaction.

Aim of the current work was to examine developmental changes in adolescents’ olfactory performance and personal significance of olfaction. In the first study olfactory identification abilities of 76 participants (31 males and 45 females aged between 10 and 18 years; M = 13.8, SD = 2.3) was evaluated with the Sniffin Stick identification test, presented in a cued and in an uncued manner. Verbal fluency was additionally examined for control purpose. In the second study 131 participants (46 males and 85 females aged between 10 and 18 years; (M = 14.4, SD = 2.2) filled in the importance of olfaction questionnaire. Odor identification abilities increased significantly with age and were significantly higher in girls as compared to boys. These effects were especially pronounced in the uncued task and partly related to verbal fluency. In line, the personal significance of olfaction increased with age and was generally higher among female compared to male participants.

Mitochondrial Ultrastructure and Glucose Signaling Pathways Attributed to the Kv1.3 Ion Channel.

Gene-targeted deletion of the potassium channel Kv1.3 (Kv1.3−∕−) results in “Super-smeller” mice with a sensory phenotype that includes an increased olfactory ability linked to changes in olfactory circuitry, increased abundance of olfactory cilia, and increased expression of odorant receptors and the G-protein, Golf. Kv1.3−∕− mice also have a metabolic phenotype including lower body weight and decreased adiposity, increased total energy expenditure (TEE), increased locomotor activity, and resistance to both diet- and genetic-induced obesity. We explored two cellular aspects to elucidate the mechanism by which loss of Kv1.3 channel in the olfactory bulb (OB) may enhance glucose utilization and metabolic rate. First, using in situ hybridization we find that Kv1.3 and the insulin-dependent glucose transporter type 4 (GLUT4) are co-localized to the mitral cell layer of the OB. Disruption of Kv1.3 conduction via construction of a pore mutation (W386F Kv1.3) was sufficient to independently translocate GLUT4 to the plasma membrane in HEK 293 cells. Because olfactory sensory perception and the maintenance of action potential (AP) firing frequency by mitral cells of the OB is highly energy demanding and Kv1.3 is also expressed in mitochondria, we next explored the structure of this organelle in mitral cells. We challenged wildtype (WT) and Kv1.3−∕− male mice with a moderately high-fat diet (MHF, 31.8 % kcal fat) for 4 months and then examined OB ultrastructure using transmission electron microscopy. In WT mice, mitochondria were significantly enlarged following diet-induced obesity (DIO) and there were fewer mitochondria, likely due to mitophagy. Interestingly, mitochondria were significantly smaller in Kv1.3−∕− mice compared with that of WT mice. Similar to their metabolic resistance to DIO, the Kv1.3−∕− mice had unchanged mitochondria in terms of cross sectional area and abundance following a challenge with modified diet. We are very interested to understand how targeted disruption of the Kv1.3 channel in the OB can modify TEE. Our study demonstrates that Kv1.3 regulates mitochondrial structure and alters glucose utilization; two important metabolic changes that could drive whole system changes in metabolism initiated at the OB.

The herbicide atrazine induces hyperactivity and compromises tadpole detection of predator chemical cues

The ability to detect chemical cues is often critical for freshwater organisms to avoid predation and find food and mates. In particular, reduced activity and avoidance of chemical cues signaling predation risk are generally adaptive behaviors that reduce prey encounter rates with predators. The present study examined the effects of the common herbicide atrazine on the ability of Cuban tree frog (Osteopilus septentrionalis) tadpoles to detect and respond to chemical cues from larval dragonfly (Libellulidae sp.) predators. Tadpoles exposed to an estimated environmental concentration of atrazine (calculated using US Environmental Protection Agency software; measured concentration, 178 μg/L) were significantly hyperactive relative to those exposed to solvent control. In addition, control tadpoles significantly avoided predator chemical cues, but tadpoles exposed to atrazine did not. These results are consistent with previous studies that have demonstrated that ecologically relevant concentrations of atrazine can induce hyperactivity and impair the olfactory abilities of other freshwater vertebrates. The authors call for additional studies examining the role of chemical contaminants in disrupting chemical communication and the quantification of subsequent impacts on the fitness and population dynamics of wildlife. Environ Toxicol Chem 2016;35:2239-2244. © 2016 SETAC.

Illuminating odors: when optogenetics brings to light unexpected olfactory abilities.

For hundreds of years, the sense of smell has generated great interest in the world literature, oenologists, and perfume makers but less of scientists. Only recently this sensory modality has gained new attraction in neuroscience when original tools issued from physiology, anatomy, or molecular biology were available to decipher how the brain makes sense of olfactory cues. However, this move was promptly dampened by the difficulties of developing quantitative approaches to study the relationship between the physical characteristics of stimuli and the sensations they create. An upswing of olfactory investigations occurred when genetic tools could be used in combination with devices borrowed from the physics of light (a hybrid technique called optogenetics) to scrutinize the olfactory system and to provide greater physiological precision for studying olfactory-driven behaviors. This review aims to present the most recent studies that have used light to activate components of the olfactory pathway, such as olfactory receptor neurons, or neurons located further downstream, while leaving intact others brain circuits. With the use of optogenetics to unravel the mystery of olfaction, scientists have begun to disentangle how the brain makes sense of smells. In this review, we shall discuss how the brain recognizes odors, how it memorizes them, and how animals make decisions based on odorants they are capable of sensing. Although this review deals with olfaction, the role of light will be central throughout.

Weak olfaction increases seed scatter‐hoarding by Siberian chipmunks: implication in shaping plant–animal interactions

Scatter‐hoarding of seeds by animals plays an essential role in seed dispersal of plants and in shaping plant–animal interactions in forest ecosystems, but the function of scatter‐hoarding behavior is still unclear. We hypothesize that weak olfactory cues between seeds and scatter‐hoarding animals would increase scatter‐hoarding. Using a rodent–plant system of Siberian chipmunks Tamias sibiricus and Korean pines Pinus koraiensis, we tested the effects on seed scatter‐hoarding intensity by measuring and modifying the seed odor intensities and the abilities of the animals to detect seed odor. Siberian chipmunks seemed to scatter‐hoard more seeds with weaker odor signals, and Siberian chipmunks with reduced olfactory ability scatter‐hoarded more seeds, supporting our hypothesis. Our studies suggest that olfaction may have played an important role in the evolution of the strength of seed odor and scatter‐hoarding behavior of animals, and in shaping plant–animal interactions.

Chemosensory Abilities in Consumers of a Western-Style Diet.

People vary in their habitual diet and also in their chemosensory abilities. In this study, we examined whether consumption of a Western-style diet, rich in saturated fat and added sugar, is associated with either poorer or different patterns of chemosensory perception, relative to people who consume a healthier diet. Participants were selected based on a food frequency questionnaire, which established whether they were likely to consume a diet either higher or lower in saturated fat and added sugar. Eighty-seven participants were tested for olfactory ability (threshold, discrimination, and identification), gustatory ability (PROP sensitivity, taste intensity, quality, and hedonics), and flavor processing (using dairy fat-sugar-odor mixtures). A Western-style diet was associated with poorer odor identification ability, greater PROP sensitivity, poorer fat discrimination, different patterns of sweetness taste enhancement, and hedonic differences in taste and flavor perception. No differences were evident for odor discrimination or threshold, in perception of taste intensity/quality (excluding PROP) or the ability of fats to affect flavor perception. The significant relationships were of small to moderate effect size, and would be expected to work against consuming a healthier diet. The discussion focuses on whether these diet-related differences precede adoption of a Western-style diet and/or are a consequence of it.

Children’s exposure to odors in everyday contexts predicts their odor awareness

A great degree of interindividual variability has been reported in measures of psychophysical olfactory performance and odor awareness in both children and adults. Previous studies have suggested the possibility that one of the factors that might contribute to this variability could be the degree of odor exposure experienced in everyday contexts. In the present study, we hypothesized that children exposed to a greater variety of odors on a more frequent basis exhibit higher odor identification, discrimination, and odor awareness scores. We have found an effect of odor exposure on one aspect of the children’s olfactory knowledge as reflected in their reports of olfactory behavior, but not olfactory abilities. In so doing, we have replicated some of the previous findings in the literature of the female advantage in the olfactory domain. Namely, we report that girls showed a more profound metacognitive understanding of their sense of smell and a greater degree of olfaction-oriented behavior, which was not accounted for by a gender difference in verbal fluency. Nevertheless, girls did not outperform boys on any of the olfactory tests. Semi-longitudinal and longitudinal studies in verbally proficient children, employing both self- and parental reports of children’s odor exposure and repeated olfactory testing, may provide insight into whether children exposed more frequently to a greater variety of odors over the longer term come to exhibit greater odor awareness and superior performance in olfactory tests.

Mind the cat: Conservation management of a protected dominant scavenger indirectly affects an endangered apex predator

Interspecific interactions are among the key factors influencing the structure of animal communities and have high relevance for conservation. However, managers, conservationists and decision-makers rarely consider the potential side-effects of single-species carnivore management for the conservation of other carnivores. We studied how management of protected brown bears (Ursus arctos) affected interspecific interactions with an endangered apex predator, the Eurasian lynx (Lynx lynx) in Slovenia. Due to large body size and superb olfactory abilities, bears are one of the most important dominant scavengers and regularly usurp kills from other large predators, a process known as kleptoparasitism. At the same time, bears throughout the world are usually actively managed through zone-specific culling regimes, supplemental feeding, and translocations. This can considerably alter bear densities and activity patterns and in turn influence interactions among carnivores. Overall, we observed that bear scavenging pressure resulted in substantial energetic losses for Eurasian lynx. The probability of lynx losing kills to bears ranged from 8 to 74% and strongly depended on local bear densities and monthly bear movement rates. Kleptoparasitic interaction intensity differed almost 3-fold between different bear management zones. Furthermore, the presence of a bear feeding site increased the odds of lynx losing kills by 5-fold compared to areas >1000m from these sites. We suggest that existing bear-feeding regimes should be reconsidered in order to reduce unwanted side-effects of this controversial practice on endangered apex predators. We also call attention to the importance of considering impacts of interspecific interactions in wildlife management and conservation.

The Pig Olfactory Brain: A Primer.

Despite the fact that pigs are reputed to have excellent olfactory abilities, few studies have examined regions of the pig brain involved in the sense of smell. The present study provides an overview of the olfactory bulb, anterior olfactory nucleus, and piriform cortex of adult pigs using several approaches. Nissl, myelin, and Golgi stains were used to produce a general overview of the organization of the regions and confocal microscopy was employed to examine 1) projection neurons, 2) GABAergic local circuit neurons that express somatostatin, parvalbumin, vasoactive intestinal polypeptide, or calretinin, 3) neuromodulatory fibers (cholinergic and serotonergic), and 4) glia (astrocytes and microglia). The findings revealed that pig olfactory structures are quite large, highly organized and follow the general patterns observed in mammals.

Rigorous Training of Dogs Leads to High Accuracy in Human Scent Matching-To-Sample Performance.

Human scent identification is based on a matching-to-sample task in which trained dogs are required to compare a scent sample collected from an object found at a crime scene to that of a suspect. Based on dogs’ greater olfactory ability to detect and process odours, this method has been used in forensic investigations to identify the odour of a suspect at a crime scene. The excellent reliability and reproducibility of the method largely depend on rigor in dog training. The present study describes the various steps of training that lead to high sensitivity scores, with dogs matching samples with 90% efficiency when the complexity of the scents presented during the task in the sample is similar to that presented in the in lineups, and specificity reaching a ceiling, with no false alarms in human scent matching-to-sample tasks. This high level of accuracy ensures reliable results in judicial human scent identification tests. Also, our data should convince law enforcement authorities to use these results as official forensic evidence when dogs are trained appropriately.

Metacognitive knowledge of olfactory dysfunction in Parkinson’s disease

It is well known that patients with Parkinson’s Disease (PD) suffer from olfactory impairments, but it is not clear whether patients are aware of their level of deficit in olfactory functioning. Since PD is a neurodegenerative disorder and its progression may be correlated with olfactory loss (Ansari & Johnson, 1975; but see also Doty, Deems, & Stellar, 1988), it is possible that these patients would be subject to metacognitive errors of over-estimation of olfactory ability (White & Kurtz, 2003). Nineteen non-demented PD patients and 19 age-matched controls were each given an objective measure of olfactory identification (the UPSIT, Doty, Shaman, Kimmelman, & Dann, 1984) and a subjective measure involving a questionnaire that asked them to self-rate both their olfactory function generally and their ability to smell each of 20 odors, 12 of which were assessed on the UPSIT. All of the PD patients showed impaired olfactory ability, as did 7 of the controls, according to the UPSIT norms. Self-rated and performance-based olfactory ability scores were significantly correlated in controls (r=.49, p=.03) but not in patients with PD (r=.20, p=.39). When the 12 odors common to both the self-rated questionnaire and UPSIT were compared, PD patients were less accurate than controls (t(36)=−4.96, p<.01) at estimating their own ability and the number of over-estimation errors was significantly higher (tone-tailed(29)=1.80, p=.04) in PD patients than in the control group, showing less metacognitive awareness of their ability than controls. These results support the idea that olfactory metacognition is often impaired in PD, as well as in controls recruited for normosmic ability (Wehling, Nordin, Espeseth, Reinvang, & Lundervold, 2011), and indicate that people with PD generally exhibit over-estimation of their olfactory ability at a rate that is higher than controls. These findings imply that PD patients, unaware of their olfactory deficit, are at greater risk of harm normally detected through olfaction, such as smoke or spoiled foods.