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Poor human olfaction is a 19th-century myth

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Abstract

It is commonly believed that humans have a poor sense of smell compared to other mammalian species. However, this idea derives not from empirical studies of human olfaction but from a famous 19th-century anatomist’s hypothesis that the evolution of human free will required a reduction in the proportional size of the brain’s olfactory bulb. The human olfactory bulb is actually quite large in absolute terms and contains a similar number of neurons to that of other mammals. Moreover, humans have excellent olfactory abilities. We can detect and discriminate an extraordinary range of odors, we are more sensitive than rodents and dogs for some odors, we are capable of tracking odor trails, and our behavioral and affective states are influenced by our sense of smell.

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... encephalization, neurons) mainly including the olfactory bulbs both for model and non-model species (e.g. Ribeiro et al. 2014, McGann 2017. Relative brain volume and other brain proxies, may not always correlate with the actual performance in comparison to more accurate proxies such as neuronal activity or the absolute neuron number (e.g. ...
... Moreover, dogs have twice the number of functional olfactory receptor genes compared to humans (Niimura et al. 2017). On the other hand, some olfactory capacities may be linked to the absolute number of neurons and for example, humans have better discriminatory and sensitivity capacities than dogs for particular odorant molecules , Oliveirapinto et al. 2014, McGann 2017. Experimental studies in dogs and humans suggested that the apparently poor human olfaction may be partially due to the current absence of behavioral demands. ...
... Therefore, are these macrosmatic and microsmatic 19th-century terms (Turner 1890) still valid concepts? Probably not (see also Laska et al. 2000, Smith et al. 2004, McGann 2017. ...
Thesis
In most tetrapods, the nasal cavity houses a bony or a cartilaginous system (i.e. turbinals or turbinates) supporting epithelium and sensory organs involved in either olfaction or heat and moisture conservation. Among extant tetrapods, mammals have on average, the largest turbinals to skull length ratio. Despite some studies in primates, Carnivora, bats, lagomorphs as well asrodents, our understanding of the selective pressures affecting turbinals remains imprecise.This PhD aims to unravel the evolutionary processes responsible for the large anatomical and morphological variations of turbinals among mammals. In the course of our work we acquired an extensive dataset of three-dimensional micro-computed tomography scans (micro-CT) in rodents and other small terrestrial mammals. We were then able to statistically test hypotheses linking turbinal morphology to ecology (e.g. diet or ecotype) and evolutionary patterns such asconvergence or evolutionary trade-off (e.g. conflict for space in the nasal cavity between different organs).The present dissertation provides a non-exhaustive review of the olfaction. In the light of our works, we discussed the methodological and conceptual limits of the field. Indeed, olfaction is a complex function relying on multifactorial processes, under various selective pressures. Olfaction may be tackled by resorting to different approaches (e.g. morphology, histology, genomics) and anatomical proxies (e.g. turbinals, olfactory bulb, vomeronasal organ). In thiscontext, our ongoing projects try to refine current functional hypotheses in studying covariation in olfactory-related organs using different anatomical proxies, immunohistochemistry, and transcriptomic.
... Human olfaction involves complex processes that detect, discriminate, and code thousands of odors (McGann, 2017). Olfactory impairments reflect deficient functionality in the periphery with variable odor thresholds or compromised central processing of the olfactory information resulting in diminished odor discrimination and identification (Frasnelli et al., 2002;Raff et al., 2008;Robles-Osorio et al., 2020;Iacono et al., 2021;Yusuf et al., 2021a). ...
... The OSNs have a lifelong regenerative capacity necessary for adequate olfaction (Lazarini and Lledo, 2011). Reduced tissue maintenance by poor basal stem cell proliferation within the epithelium can generate hyposmia (a significant reduction in olfactory abilities), anosmia (complete loss of olfaction), or olfactory threshold deficiencies due to the lack of neural signals in the OB (Goncalves and Goldstein, 2016;McGann, 2017). ...
... Olfactory disorders are associated with many causes like nasal inflammation, upper olfactory tract abnormalities, neurological pathologies, and aging (Huttenbrink et al., 2013;Schriever et al., 2014;Kar et al., 2015). Moreover, olfaction strongly influences human behavior: a wide range of environmental odors primes our safety (e.g., avoiding fire, gas leakage, or rotten food) but also influences eating behavior (e.g., associating memories and emotions with food) and social interactions (McGann, 2017). Initially, olfactory impairments remain unnoticed, forcing the individuals into situations where they must deal with daily issues like feeding, safety, and social situations, which, in many cases, lead to anxiety and depression (Sivam et al., 2016;Kondo et al., 2020). ...
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Chronic kidney disease (CKD) is a multifactorial pathology that progressively leads to the deterioration of metabolic functions and results from deficient glomerular filtration and electrolyte imbalance. Its economic impact on public health is challenging. Mexico has a high prevalence of CKD that is strongly associated with some of the most common metabolic disorders like diabetes and hypertension. The gradual loss of kidney functions provokes an inflammatory state and endocrine alterations affecting several systems. High serum levels of prolactin have been associated with CKD progression, inflammation, and olfactory function. Also, the nutritional status is altered due to impaired renal function. The decrease in calorie and protein intake is often accompanied by malnutrition, which can be severe at advanced stages of the disease. Nutrition and olfactory functioning are closely interconnected, and CKD patients often complain of olfactory deficits, which ultimately can lead to deficient food intake. CKD patients present a wide range of deficits in olfaction like odor discrimination, identification, and detection threshold. The chronic inflammatory status in CKD damages the olfactory epithelium leading to deficiencies in the chemical detection of odor molecules. Additionally, the decline in cognitive functioning impairs the capacity of odor differentiation. It is not clear whether peritoneal dialysis and hemodialysis improve the olfactory deficits, but renal transplants have a strong positive effect. In the present review, we discuss whether the olfactory deficiencies caused by CKD are the result of the induced inflammatory state, the hyperprolactinemia, or a combination of both.
... Odor, smell, fragrance, scent, aroma, all these words refer to olfactory perception, which has been falsely defined as being poor, crude and useless (McGann, 2017;. ...
... Indeed, a stimulus that is less easily categorized could then undergo a less deep encoding than other easily categorizable stimuli, leading to decreased recognition performance (Craik and Lockhart, 1972;Craik and Tulving, 1975). Another explanation may be that the odor perceptual system is implemented differently than other sensory systems, being for example less tied to semantization processes , or that there is poor olfactory ability linked to a poor general attention to olfaction in everyday life (McGann, 2017). ...
... Odor recognition may be impaired relative to stimuli from other sensory modalities for several reasons. It is possible that the low attention that most humans pay to odors impairs their recognition memory (McGann, 2017). It has indeed been shown that people who are more aware of odors in their everyday life are better able to recognize odors (Arshamian et al., 2011). ...
Thesis
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Episodic memory concerns the re-experience of past personal events anchored in their encoding context. These episodic memories are not fixed: their content is influenced by the sensory modality of the recall cue. For example, memories evoked by smells are known to be less frequent, more surprising, vivid, emotional, and older than memories evoked by images or words. These phenomena are commonly explained by the close and direct anatomical links that exist between the primary olfactory, memory, and emotional brain structures. However, odors have rarely been compared to cues that also possess privileged links to memory, such as music and faces, both behaviorally and functionally. This thesis has two main objectives: 1) To identify and characterize the particularities of episodic memory attributable to the sensory modality of the recall cue (Studies 1 and 2); 2) To study the dynamics of the neural networks underlying episodic recall and more specifically the interactions that are modulated differently according to the sensory modality of the recall cue (Study 3). To test the hypothesis that emotion would be an essential factor in the particularity of olfactory cues to recall a memory, the secondary aim of this thesis is to evaluate the differential effect of emotion of the episodic recall cue as a function of its sensory modality. To meet our objectives and to allow for the study of episodic memory in the most ecological conditions possible, we have developed a non-immersive virtual reality protocol that can be declined in several versions allowing the encoding and recall of complex and multisensory episodes experienced in the laboratory. By using neutral stimuli, the first study showed that the sensory modality of the recall cue influenced recognition and episodic memory performance. Faces were very well recognized and very good cues for episodic memory; smells were less well recognized, but were good cues for episodic memory; musical excerpts, although very well recognized were not good cues for episodic memory. By using emotional stimuli, the second study confirmed the previous results, and clarified the effects of emotion on episodic memory performance by showing that the emotional valence of the recall cue favors globally all memory stages. The most pleasant and unpleasant stimuli, compared to the most neutral ones, were associated with better memory performance. In addition, the pronounced effectiveness of odors in evoking episodic recall was associated with participants’ individual motivation to resample the stimulus. This study also highlighted the importance of the ecological relevance of the stimuli, with the virtualization of faces leading to the suppression of their superiority as a memory cue in comparison to odors and music. The third study, still in progress, confirms the memory strength of odors, when they are pleasant, to recall the different dimensions of an episode. Preliminary data suggest that musical and olfactory cues in episodic memory activate autobiographical memory networks. In conclusion, our studies reveal an effect of the sensory modality of the recall cue on episodic recall and suggest that this effect is associated with the emotion carried by these cues. Odors appear to be singular recall cues, associated with average recognition performance, but favoring accurate recollection of episodic memories. This recollection is driven by the motivation the odors have generated. Music, although very well recognized, leads to less correct recall of associated episodic dimensions. Finally, visual stimuli seem to differ according to their ecological relevance, with more efficient cueing and more complete memory being associated with more ecologically relevant stimuli.
... This statement is largely acknowledged with respect to other terrestrial mammals, but it is often rejected with respect to humans. In humans, the role of olfaction has been denigrated (45) in part because of various social taboos (45), culminating in the view that olfaction is unimportant for human sociality (46). Recent evidence, however, implies a significant role for olfaction in human social interaction. ...
... This statement is largely acknowledged with respect to other terrestrial mammals, but it is often rejected with respect to humans. In humans, the role of olfaction has been denigrated (45) in part because of various social taboos (45), culminating in the view that olfaction is unimportant for human sociality (46). Recent evidence, however, implies a significant role for olfaction in human social interaction. ...
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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.
... The study of our olfactory sense has seen an increase during recent years with the realization that the olfactory system can be a marker of neurodegeneration in aging, neurological and neuropsychiatric disorders (reviewed in Bhatia-Dey and Heinbockel 2021). Our olfactory sense is relevant for dayto-day behavior as well as for our quality of life (Mann, 2002;Croy et al., 2014;McGann, 2017). It has been shown that declining olfactory acuity and olfactory deficits emerge either as very first symptoms or as prodromal symptoms of progressive neurodegeneration. ...
... OSNs with the same receptor protein send their axon to the same location in the brain, namely one of more than 5,000 glomeruli in the human olfactory bulb, compared to about 2000 glomeruli in mice and rats (Maresh et al., 2008;McGann, 2017). The axon terminal of each OSN forms synaptic contacts with dendrites of olfactory bulb interneurons (juxtaglomerular cells) and output neurons, the mitral and tufted cells. ...
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The recent increase in the number of patients with post-viral olfactory dysfunction (PVOD) following the outbreak of COVID-19 has raised the general interest in and concern about olfactory dysfunction. At present, no clear method of treatment for PVOD has been established. Currently the most well-known method to improve the symptoms of olfactory dysfunction is “olfactory training” using essential oils. The essential oils used in olfactory training typically include rose, lemon, clove, and eucalyptus, which were selected based on the odor prism hypothesis proposed by Hans Henning in 1916. He classified odors based on six primary categories or dimensions and suggested that any olfactory stimulus fits into his smell prism, a three-dimensional space. The term “olfactory training” has been used based on the concept of training olfactory sensory neurons to relearn and distinguish olfactory stimuli. However, other mechanisms might contribute to how olfactory training can improve the recovery of the olfactory sense. Possibly, the essential oils contain chemical constituents with bioactive properties that facilitate the recovery of the olfactory sense by suppressing inflammation and enhancing regeneration. In this review, we summarize the chemical constituents of the essential oils of rose, lemon, clove, and eucalyptus and raise the possibility that the chemical constituents with bioactive properties are involved in improving the symptoms of olfactory dysfunction. We also propose that other essential oils that contain chemical constituents with anti-inflammatory effects and have binding affinity with SARS-CoV-2 can be new candidates to test their efficiencies in facilitating the recovery.
... Capitalising on human's highly evolved and sensitive olfactory capabilities (McGann 2017), smells are harnessed to impact the behaviours of those exposed to them. Olfactory cues of a loved one, in this way, may improve sleep (Hofer and Chen 2020) and particular smells are released intentionally both inside and outside shops to nudge consumers into purchasing products (Jellinek 1997;Sandell 2019) by tapping into conditioned pleasant associations. ...
... This approach of attempting to more specifically define social drinking mirrors similar published approaches2017) Content courtesy of Springer Nature, terms of use apply. Rights reserved. ...
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Background It is well known that, owing to associative processing, olfactory cues can impact memory, emotion and behaviour. Research also points to a link between the smells of particular substances and craving. Yet, to date, little research has investigated how smell may impact other cognitive processes that are known to drive alcohol consumption. Aim To assess how exposure to alcohol-related (vodka) relative to neutral (citrus) olfactory cues impacts inhibitory control and attentional bias. Method Participants took part in a go/no-go (Study 1) and Stroop task (Study 2) while wearing masks that were pre-treated with vodka or citrus oil of equivalent intensity. Study 1 results Response error rates were higher in participants in the alcohol-related (versus neutral) olfactory condition, with no interaction between olfactory and visual cue. Study 2 results Responses to alcohol-related versus neutral words were similar, while performance appeared significantly impaired among participants wearing alcohol (relative to citrus) infused masks. Conclusion The smell of alcohol may impair signal detection performance on the go/no-go and Stroop task. As inhibitory control and attentional processes are known to be associated with decisions to drink or exercise restraint, these results may have implications for our understanding of alcohol consumption and for tailoring interventions.
... [33][34][35] When considering how humans and rodents might differ during navigation, differences in sensory perception are important. Although humans have binocular vision, they may differ in olfaction 36 and lack the tactility of whiskers. Meanwhile, rodents have a larger visual field of view, lower visual acuity, and can move their eyes independently. ...
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Much of our understanding of navigation comes from the study of individual species, often with specific tasks tailored to those species. Here, we provide a novel experimental and analytic framework integrating across humans, rats, and simulated reinforcement learning (RL) agents to interrogate the dynamics of behavior during spatial navigation. We developed a novel open-field navigation task (“Tartarus maze”) requiring dynamic adaptation (shortcuts and detours) to frequently changing obstructions on the path to a hidden goal. Humans and rats were remarkably similar in their trajectories. Both species showed the greatest similarity to RL agents utilizing a “successor representation,” which creates a predictive map. Humans also displayed trajectory features similar to model-based RL agents, which implemented an optimal tree-search planning procedure. Our results help refine models seeking to explain mammalian navigation in dynamic environments and highlight the utility of modeling the behavior of different species to uncover the shared mechanisms that support behavior.
... Over the past decades, in the scientific literature on the physiology and genetics of smell, objections have been repeatedly expressed to the classical concepts of attributing humans to the group of microsmatics, i.e. mammals with a poorly developed olfactory analyzer and an insignificant role of odors in everyday life (Schaal, 1988;Shepherd, 2004;McGann, 2017;Roberts et al., 2020). Numerous comparative behavioral studies performed on various mammalian species and in humans have shown that sensitivity to odors is not directly related to the size of the receptor pool and BIOLOGY BULLETIN REVIEWS Vol. ...
... For most mammals, this chemosensory interaction relays vital information to the organism, participating in avoiding danger, finding potential mating partners, or identifying food. Despite a common belief than humans have a poor sense of smell compared with other mammals, recent research has established that human smell is remarkably sophisticated [2]. Odor detection in humans is notably associated with social, emotional, and feeding decisions. ...
Article
Olfactory perception guides daily decisions regarding food consumption, social interactions, and predator avoidance in all mammalian species. Volatile inputs, comprising odorants and pheromones, are relayed to the olfactory bulb (OB) from nasal sensory neurons cells and transferred to secondary processing regions within the brain. Olfaction has recently been shown to shape homeostatic and maladaptive processes of energy intake and expenditure through neuronal circuits involving the medial basal hypothalamus. Reciprocally, gastrointestinal hormones, such as ghrelin and leptin, the secretion of which depends on satiety and adiposity levels, might also influence olfactory sensitivity to alter food-seeking behaviors. Here, in addition to reviewing recent updates on identifying these neuronal networks, we also discuss how bidirectional neurocircuits existing between olfactory and energy processing centers can become dysregulated during obesity.
... While this study was not designed to directly address this hypothesis and may suffer from selection bias, these data support the hypothesis that the primate olfactory gene repertoire has degenerated over time. The functional implications of this degeneration remain unclear [40,41]. ...
Article
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The olfactory system combines input from multiple receptor types to represent odor information, but there are few explicit examples relating olfactory receptor (OR) activity patterns to odor perception. To uncover these relationships, we performed genome-wide scans on odor-perception phenotypes for ten odors in 1000 Han Chinese and validated results for six of these odors in an ethnically diverse population (n = 364). In both populations, consistent with previous studies, we replicated three previously reported associations (β-ionone/OR5A1, androstenone/OR7D4, cis-3-hexen-1-ol/OR2J3 LD-band), but not for odors containing aldehydes, suggesting that olfactory phenotype/genotype studies are robust across populations. Two novel associations between an OR and odor perception contribute to our understanding of olfactory coding. First, we found a SNP in OR51B2 that associated with trans-3-methyl-2-hexenoic acid, a key component of human underarm odor. Second, we found two linked SNPs associated with the musk Galaxolide in a novel musk receptor, OR4D6, which is also the first human OR shown to drive specific anosmia to a musk compound. We noticed that SNPs detected for odor intensity were enriched with amino acid substitutions, implying functional changes of odor receptors. Furthermore, we also found that the derived alleles of the SNPs tend to be associated with reduced odor intensity, supporting the hypothesis that the primate olfactory gene repertoire has degenerated over time. This study provides information about coding for human body odor, and gives us insight into broader mechanisms of olfactory coding, such as how differential OR activation can converge on a similar percept.
... Humans have the best sound localization ability of primates, and among mammals are only outranked by cetaceans (Heffner and Heffner, 2016). On the other hand, visual ability in primates has been proposed to be inversely related to olfactory ability (Gilad et al., 2004) but this relationship is disputed (Gilad et al., 2007;Matsui et al., 2010;McGann, 2017). ...
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Research on the origin of vision and vision loss in naturally “blind” animal species can reveal the tasks that vision fulfills and the brain's role in visual experience. Models that incorporate evolutionary history, natural variation in visual ability, and experimental manipulations can help disentangle visual ability at a superficial level from behaviors linked to vision but not solely reliant upon it, and could assist the translation of ophthalmological research in animal models to human treatments. To unravel the similarities between blind individuals and blind species, we review concepts of 'blindness' and its behavioral correlates across a range of species. We explore the ancestral emergence of vision in vertebrates, and the loss of vision in blind species with reference to an evolution-based classification scheme. We applied phylogenetic comparative methods to a mammalian tree to explore the evolution of visual acuity using ancestral state estimations. Future research into the natural history of vision loss could help elucidate the function of vision and inspire innovations in how to address vision loss in humans.
... The number of genes expressing odour detection through the nose constitutes one of the largest gene families in the genome (Buck and Axel, 1991, p. 183), perhaps up to 3% of the total genome which would make it second only to the immune system (Haviland-Jones and Wilson, 2010, p. 236). The human sense of smell compares rather favourably with that of dogs and rats (see McGann, 2017, for a review), and its discriminatory powers might be several magnitudes larger than what was previously believed (Bushdid et al., 2014). ...
Article
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The smellscape is the olfactory environment as perceived and understood, consisting of odours and scents from multiple smell sources. To what extent can audiovisual information evoke the smells of a real, complex, and multimodal environment? To investigate smellscape imagination, we compared results from two studies. In the first, onsite participants ( N = 15) made a sensory walk through seven locations of an open-air market. In the second, online participants ( N = 53) made a virtual walk through the same locations reproduced with audio and video recordings. Responses in the form of free-form verbal annotations, ratings with semantic scales, and a ‘smell wheel’, were analysed for environmental quality, smell source type and strength, and hedonic tone. The degree of association between real and imagined smellscapes was measured through canonical correlation analysis. Hedonic tone, as expressed through frequency counts of keywords in free-form annotations was significantly associated, suggesting that smell sources might generally be correctly inferred from audiovisual information, when such imagination is required. On the other hand, onsite ratings of olfactory quality were not significantly associated with online ratings of audiovisual reproductions, when participants were not specifically asked to imagine smells. We discuss findings in the light of cross-modal association, categorisation, and memory recall of smells.
... As diurnal apes, we are 'blinded by vision', studying the sensory modalities for which we have greater conscious awareness [9]. Events in human history have also contributed to human olfaction being underestimated and understudied [20,21]. Naturalistic spatial orientation to odours has been addressed in even fewer studies [22][23][24]. ...
Article
To make maps from airborne odours requires dynamic respiratory patterns. I propose that this constraint explains the modulation of memory by nasal respiration in mammals, including murine rodents (e.g. laboratory mouse, laboratory rat) and humans. My prior theories of limbic system evolution offer a framework to understand why this occurs. The answer begins with the evolution of nasal respiration in Devonian lobe-finned fishes. This evolutionary innovation led to adaptive radiations in chemosensory systems, including the emergence of the vomeronasal system and a specialization of the main olfactory system for spatial orientation. As mammals continued to radiate into environments hostile to spatial olfaction (air, water), there was a loss of hippocampal structure and function in lineages that evolved sensory modalities adapted to these new environments. Hence the independent evolution of echolocation in bats and toothed whales was accompanied by a loss of hippocampal structure (whales) and an absence of hippocampal theta oscillations during navigation (bats). In conclusion, models of hippocampal function that are divorced from considerations of ecology and evolution fall short of explaining hippocampal diversity across mammals and even hippocampal function in humans. This article is part of the theme issue ‘Systems neuroscience through the lens of evolutionary theory’.
... In particular, olfaction is important to humans: it's used to develop object awareness, perceiving the season and atmosphere of a place and a fundamental part of eating. It influences our behavior and offers greater potential for survival by allowing us to detect hazards in food and in the environment [1,2]. Our sense of odor uses the olfactory nerve to connect the external world directly to the limbic system, which is composed of structures in the brain that deal with emotions (e.g., sadness, anger, happiness, fear, the startle reflex [3], voice pitch [4], pain [5], and memory [6,7]. ...
Article
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Olfaction has not been explored in virtual reality environments to the same extent as the visual and auditory senses. Much less research has been done with olfactory devices, and very few of them can be easily integrated into virtual reality applications. The inclusion of odor into virtual reality simulations using a chemical device involves challenges such as possible diffusion into undesired areas, slow dissipation, the definition of various parameters (e.g., concentration, frequency, and duration), and an appropriate software solution for controlling the diffusion of the odor. This paper aims to present a non-intrusive, mobile, low cost and wearable olfactory display, and a software service that allows the developer to easily create applications that include olfactory stimuli integrated with virtual reality headset glasses. We also present a case study conducted with 32 people to evaluate their satisfaction when using the olfactory display. Our findings indicate that our solution works as expected, producing odor properly and being easy to integrate to applications. Supplementary information: The online version contains supplementary material available at 10.1007/s00530-022-00908-8.
... The prominent role of odors in people's life is well known [1], however not all humans pay attention to odors in the environment in the same way [2]. There are individuals that a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 ...
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The degree of attention individuals pay to olfactory cues (called odor awareness) influences the role of odors in everyday life. Particularly, odors produced by the human body (i.e., social odors) are able to carry a wide variety of information and to elicit a broad spectrum of emotional reactions, making them essential in interpersonal relationships. Hence, despite the assessment of awareness toward social odors is crucial, a proper tool is still lacking. Here, we designed and initially validated the Social Odor Scale (SOS), a 12-item scale designed to measure the individual differences in awareness towards different social odors. In Study 1, an exploratory factor analysis (EFA; KMO test: MSA = 0.78; Bartlett’s test: χ ² (78) = 631.34, p < 0.001; Chi-squared test: χ ² (42) = 71.84, p = 0.003) suggests that the three factors structure was the model that best fit with the Italian version of the scale. The confirmatory factor analysis (CFA) supports a second-order model with one higher-order factor representing social odor awareness in general and three lower-order factors representing familiar, romantic partner, and stranger social odors. The final version of the scale presented a good fit (RMSEA = 0.012, SRMR = 0.069, CFI = 0.998, TLI = 0.997). In Study 2, CFA was performed in the German version of the scale confirming the validity of scale structure. Study 3 and 4 revealed that SOS total score and its subscales were positively correlated with other validated olfactory scales, but not with olfactory abilities. Moreover, SOS was found to be related to the gender of the participants: women reported to be more aware to social odors and, specifically, to familiar social odors than men. Overall, the results indicated that SOS is a valid and reliable instrument to assess awareness toward social odors in everyday life.
... The human sense of smell has been demonstrated to be surprisingly good when compared with that of other mammals [48,49]. Several studies have shown that humans even outperform dogs, mice, and rats with regard to their threshold sensitivity with certain odorants [50][51][52]. ...
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Mammalian body odour conveys cues about an individual’s emotional state that can be recognised by conspecifics. Thus far, little attention has been paid to interspecific odour communication of emotions, and no studies have examined whether humans are able to recognise animal emotions from body odour. Thus, the aim of the present study was to address this question. Body odour samples were collected from 16 two-year-old thoroughbred horses in fear and non-fear situations, respectively. The horse odour samples were then assessed by 73 human odour raters. We found that humans, as a group, were able to correctly assign whether horse odour samples were collected under a fear- or a non-fear condition, respectively. Furthermore, they perceived the body odour of horses collected under the fear condition as more intense, compared with the non-fear condition. An open question remains, which is whether humans could simply distinguish between little versus much sweat and between high intensity versus low intensity or were able to recognise horses’ fear and non-fear emotions. These results appear to fit the notion that the ability to recognise emotions in other species may present an advantage to both the sender and the receiver of emotional cues, particularly in the interaction between humans and domesticated animals. To conclude, the present results indicate that olfaction might contribute to the human recognition of horse emotions. However, these results should be addressed with caution in light of the study’s limitations and only viewed as exploratory for future studies.
... Human olfaction has been mistakenly considered as very poor for decades, but recent studies have highlighted that humans actually have very fine olfactory abilities (McGann, 2017). In addition, humans can communicate, through chemosensory cues, socially relevant information, including sickness (e.g., Olsson et al., 2014), emotional state (fear, stress, happiness) (de Groot et al., 2015(de Groot et al., , 2020Mujica-Parodi et al., 2009), or personality traits (Sorokowska, 2013a(Sorokowska, , 2013bSorokowska et al., 2012). ...
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Several physical features influence the perception of how cooperative a potential partner is. While previous work focused on face and voice, it remains unknown whether body odours influence judgements of cooperativeness and if odour‐based judgements are accurate. Here, we first collected axillary odours of cooperative and uncooperative male donors through a public good game and used them as olfactory stimuli in a series of tasks examining whether and how they influence cooperative decision‐making in an incentivized economic game and ratings of cooperativeness. Our results show that having access to the donor's body odours provided a strategic advantage to women during economic decisions (but not to men): with age, women were more likely to cooperate with cooperative men and to avoid interacting with uncooperative men. Ratings of cooperativeness were nonetheless unrelated to the donors’ actual cooperativeness. Finally, while men with masculine and intense body odours were judged less cooperative, we found no evidence that donors’ actual cooperativeness was associated with less masculine or less intense body odour. Overall, our findings suggest that, as faces and voices, body odours influence perceived cooperativeness and might be used accurately and in a non‐aware manner as olfactory cues of cooperativeness, at least by women.
... Makrosmatiker wie z. B. Mäuse, deren Überleben von einem intakten Geruchssinn abhängt) [13]. McGann beschreibt sehr anschaulich, wie der Mythos eines unterentwickelten Geruchssinns beim Menschen in der Wissenschaft und somit auch im Bewusstsein der Bevölkerung verankert wurde. ...
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Zusammenfassung Zunehmende Evidenz belegt, dass der menschliche Geruchssinn eine große Bedeutung für die Gesundheit und Lebensqualität einnimmt sowie eine besondere Leistungsfähigkeit aufweist. Durch die häufig auftretende Riechstörung im Rahmen der Infektion mit SARS-CoV‑2 rückt das klinische Interesse in der Behandlung von Patienten mit Verlust des Geruchs- und Geschmackssinnes in den Vordergrund. Der vorliegende Artikel beleuchtet wichtige Aspekte in der Diagnose und Therapie der chemischen Sinne.
... Humans also have a well-developed sense of olfaction but are not as behaviorally dependent upon their sense of smell to interact with the surrounding world, and to date, there have been no reports of neuroinvasion via inhalation into the NC of humans [1,18,19]. However, there is evidence for prions binding to dust collected from scrapie-affected farms and speculation that the olfactory bulb might serve as an entry site for prion neuroinvasion based on the involvement of olfactory structures in animal and human prion diseases [20][21][22][23][24][25]. ...
Article
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Prion diseases, or transmissible spongiform encephalopathies (TSEs), are a class of fatal neurodegenerative diseases caused by the entry and spread of infectious prion proteins (PrPSc) in the central nervous system (CNS). These diseases are endemic to certain mammalian animal species that use their sense of smell for a variety of purposes and therefore expose their nasal cavity (NC) to PrPSc in the environment. Prion diseases that affect humans are either inherited due to a mutation of the gene that encodes the prion protein, acquired by exposure to contaminated tissues or medical devices, or develop without a known cause (referred to as sporadic). The purpose of this review is to identify components of the NC that are involved in prion transport and to summarize the evidence that the NC serves as a route of entry (centripetal spread) and/or a source of shedding (centrifugal spread) of PrPSc, and thus plays a role in the pathogenesis of the TSEs.
... At least for mammals, the absolute and relative size of the OB as a proxy of the olfactory capability of a species has been questioned [62]. The number of neurons has been proposed as a more reliable parameter to consider [48,60]. ...
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The olfactory system is constituted in a consistent way across vertebrates. Nasal structures allow water/air to enter an olfactory cavity, conveying the odorants to a sensory surface. There, the olfactory neurons form, with their axons, a sensory nerve projecting to the telencephalic zone—named the olfactory bulb. This organization comes with many different arrangements, whose meaning is still a matter of debate. A morphological description of the olfactory system of many teleost species is present in the literature; nevertheless, morphological investigations rarely provide a quantitative approach that would help to provide a deeper understanding of the structures where sensory and elaborating events happen. In this study, the peripheral olfactory system of the Antarctic silverfish, which is a keystone species in coastal Antarctica ecosystems, has also been described, employing some quantitative methods. The olfactory chamber of this species is connected to accessory nasal sacs, which probably aid water movements in the chamber; thus, the head of the Antarctic silverfish is specialized to assure that the olfactory organ keeps in contact with a large volume of water—even when the fish is not actively swimming. Each olfactory organ, shaped like an asymmetric rosette, has, in adult fish, a sensory surface area of about 25 mm2, while each olfactory bulb contains about 100,000 neurons. The sensory surface area and the number of neurons in the primary olfactory brain region show that this fish invests energy in the detection and elaboration of olfactory signals and allow comparisons among different species. The mouse, for example—which is considered a macrosmatic vertebrate—has a sensory surface area of the same order of magnitude as that of the Antarctic silverfish, but ten times more neurons in the olfactory bulb. Catsharks, on the other hand, have a sensory surface area that is two orders of magnitude higher than that of the Antarctic silverfish, while the number of neurons has the same order of magnitude. The Antarctic silverfish is therefore likely to rely considerably on olfaction.
... The olfactive system is highly evolved to translate chemical information in food and our surroundings into essential impressions of beauty, events, or even imminent danger [1][2][3]. The chemical information in the environment is generally sensed through the nose directly (orthonasally), whereas the impact of food aroma is sensed both orthonasally and retronasally (through the back of the throat) [4]. ...
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Predicting the sensory properties of compounds is challenging due to the subjective nature of the experimental measurements. This testing relies on a panel of human participants and is therefore also expensive and time-consuming. We describe the application of a state-of-the-art deep learning method, Alchemite™, to the imputation of sparse physicochemical and sensory data and compare the results with conventional quantitative structure–activity relationship methods and a multi-target graph convolutional neural network. The imputation model achieved a substantially higher accuracy of prediction, with improvements in R2 between 0.26 and 0.45 over the next best method for each sensory property. We also demonstrate that robust uncertainty estimates generated by the imputation model enable the most accurate predictions to be identified and that imputation also more accurately predicts activity cliffs, where small changes in compound structure result in large changes in sensory properties. In combination, these results demonstrate that the use of imputation, based on data from less expensive, early experiments, enables better selection of compounds for more costly studies, saving experimental time and resources.
... Human olfaction is often portrayed as inferior to the olfactory systems of other species (Kolb & Whishaw 2015;McGann 2017) and given the status of a secondary sense. However, human olfaction is powerful, subtle, and complex. ...
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Introduction Previous research suggests that putrescine — the chemical compound that gives decomposing organic matter its distinctive odor — may trigger an inborn evolutionary mechanism that prompts individuals to avoid the smell of decay. The purpose of these two experiments was to investigate the effects of exposure to putrescine on human cognition. Methods Two between-subjects experiments (experiment 1 N = 109; experiment 2 N = 108) compared individuals exposed to either putrescine, ammonia, or water. Experiment 1 measures included odorant ratings (i.e., intensity, familiarity, repugnance, goodness), implicit measures (i.e., word completion task, moral judgment vignettes, and opinions on the death penalty), and explicit measures (i.e., death attitudes, self-esteem, and life satisfaction); experiment 2 measures included odorant ratings and life satisfaction. Results In experiment 1, there were no differences by odorant condition on implicit measures; however, those exposed to putrescine reported higher life satisfaction than those exposed to water. These results were replicated in experiment 2. Conclusions Exposure to putrescine may activate psychological threat management processes, which are then interpreted as higher life satisfaction. Implications Human olfactory perception is sensitive to putrescine, and putrescine may exert some subtle psychological effects on human cognition.
... Olfaction is a major sensory input for mice to explore their surroundings. Although the importance of olfaction for humans has only recently been appreciated 38 , it has been known for a long time that humans rely heavily on their visual and auditory inputs for normal individual and social activities. Of note, IGF1 signalling is enriched in and important for the integrity of visual and hearing systems 39,40 . ...
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Animals constantly receive various sensory stimuli, such as odours, sounds, light and touch, from the surrounding environment. These sensory inputs are essential for animals to search for food and avoid predators, but they also affect their physiological status, and may cause diseases such as cancer. Malignant gliomas—the most lethal form of brain tumour1—are known to intimately communicate with neurons at the cellular level2,3. However, it remains unclear whether external sensory stimuli can directly affect the development of malignant glioma under normal living conditions. Here we show that olfaction can directly regulate gliomagenesis. In an autochthonous mouse model that recapitulates adult gliomagenesis4–6 originating in oligodendrocyte precursor cells (OPCs), gliomas preferentially emerge in the olfactory bulb—the first relay of brain olfactory circuitry. Manipulating the activity of olfactory receptor neurons (ORNs) affects the development of glioma. Mechanistically, olfaction excites mitral and tufted (M/T) cells, which receive sensory information from ORNs and release insulin-like growth factor 1 (IGF1) in an activity-dependent manner. Specific knockout of Igf1 in M/T cells suppresses gliomagenesis. In addition, knocking out the IGF1 receptor in pre-cancerous mutant OPCs abolishes the ORN-activity-dependent mitogenic effects. Our findings establish a link between sensory experience and gliomagenesis through their corresponding sensory neuronal circuits. A mouse model of gliomagenesis reveals that olfaction can directly regulate the genesis of gliomas, showing that sensory experience and gliomagenesis are linked and providing insight into the neural circuitry involved.
... Specifically, the analysis of this number of receptors (or gas sensors) used in eNoses is still quite distant from their biological inspiration [19]. An exception was the contribution of Marco et al. [20], who in 2014 proposed the largest eNose reported, which was based on the combination of 96 MOX gas sensors (including 12 different sensor types) and four arrays of up to 4096 chemical gas sensors, with the objective of exploring the development of neuro-bio-inspired computation. ...
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The use of electronic noses (eNoses) as analysis tools are growing in popularity; however, the lack of a comprehensive, visual representation of how the different classes are organized and distributed largely complicates the interpretation of the classification results, thus reducing their practicality. The new contributions of this paper are the assessment of the multivariate classification performance of a custom, low-cost eNose composed of 16 single-type (identical) MOX gas sensors for the classification of three volatiles, along with a proposal to improve the visual interpretation of the classification results by means of generating a detailed 2D class-map representation based on the inverse of the orthogonal linear transformation obtained from a PCA and LDA analysis. The results showed that this single-type eNose implementation was able to perform multivariate classification, while the class-map visualization summarized the learned features and how these features may affect the performance of the classification, simplifying the interpretation and understanding of the eNose results.
... A smell or odour can induce strong emotional feelings, alter behaviour and can act as a stimulus to the retrieval of autobiographical memory [2][3][4][5]. However, in the hierarchy of human senses, smell or olfaction is often underappreciated and inappropriately considered inferior when compared with olfactory performance of other mammals and to the other human sense modalities [6]. ...
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Virtual reality (VR) headsets provide immersive audio-visual experiences for users, but usually neglect to provide olfactory cues that can provide additional information about our environment in the real world. This paper examines whether the introduction of smells into the VR environment enhances users’ experience, including their sense of presence through collection of both psychological and physiological measures. Using precise odour administration with an olfactometer, study participants were exposed to smells while they were immersed in the popular PlayStation VR game “Resident Evil 7”. A within-subject study design was undertaken where participants (n = 22) walked-through the same VR environment twice, with or without the introduction of associated congruent odour stimuli. Directly after each gameplay, participants completed a questionnaire to determine their sense of presence from the overall gameplay and their sense of immersion in each of the virtual scenes. Additionally, physiological measurements (heart rate, body temperature and skin electrodermal activity) were collected from participants (n = 11) for each gameplay. The results showed the addition of odours significantly increased participants’ sense of spatial presence in the VR environment compared to VR with no odour. Participants also rated the realism of VR experience with odour higher compared to no odour, however odour addition did not result in change in emotional state of participants (arousal, pleasure, dominance). Further, the participants’ physiological responses were impacted by the addition of odour. Odour mediated physiological changes were dependent on whether the VR environment was novel, as the effect of odour on physiological response was lost when participants experienced the aroma on the second gameplay. Overall, the results indicate the addition of odours to a VR environment had a significant effect on both the psychological and physiological experience showing the addition of smell enhanced the VR environment. The incorporation of odours to VR environments presents an opportunity to create a more immersive experience to increase a person’s presence within a VR environment. In addition to gaming, the results have broader applications for virtual training environments and virtual reality exposure therapy.
... The rodent olfactory bulb is a crucial part of a neuronal circuit whose sensory functionality can determine the animal's immediate survival via activities such as foraging, predator recognition, social interaction, reproduction, and many other aspects of behavior (21). Neurons present in the olfactory bulb form several connections with various structures of the brain (22). Through efferent connections to the amygdala and hippocampus, the olfactory bulb sends information to limbic structures where the modulation and orchestration of emotional and behavioral responses occur (21). ...
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Epidemiological evidence shows that clinical features and comorbidities in temporal lobe epilepsy (TLE) may have different manifestations depending on the sex of patients. However, little is known about how sex-related mechanisms can interfere with the processes underlying the epileptic phenomenon. The findings of this study show that male rats with epilepsy in the pilocarpine model have longer-lasting and more severe epileptic seizures, while female rats have a higher frequency of epileptic seizures and a greater number of seizure clusters. Significant sex-linked pathological changes were also observed: epileptic brains of male and female rats showed differences in mass reduction of 41.8% in the amygdala and 18.2% in the olfactory bulb, while loss of neuronal cells was present in the hippocampus (12.3%), amygdala (18.1%), and olfactory bulb (7.5%). Another important sex-related finding was the changes in non-neuronal cells with increments for the hippocampus (36.1%), amygdala (14.7%), and olfactory bulb (37%). Taken together, our study suggests that these neuropathological changes may underlie the differences in the clinical features of epileptic seizures observed in male and female rats.
... Direct distribution through the nasal cavity may be a potential pathway to the brain. However, the relative size of the olfactory bulb compared to the rest of the brain is very small in primates including humans, composing about 0.01% of the human brain by volume compared to 2% of the mouse brain 21 . Whether the same can happen in humans is a topic of future research. ...
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Turmerones (α-turmerone, β-turmerone, and ar-turmerone) are the major volatile compounds in turmeric (Curcuma longa), a perennial herb of the ginger family. We previously reported that inhaled volatile turmerones could be transferred in the blood and organs. However, the difference between the two pathways, oral administration and inhalation, and the effect of inhaled turmerones on biological activities remain unknown. In this study, we compared the distribution patterns of turmerones after oral administration and inhalation. The relative levels (concentrations of turmerones in each organ/serum) in the lung, olfactory bulb, brain, heart, kidney, and epididymal fat in the inhalation group tended to be, or are significantly, higher than in the oral administration group. The relative levels of brown adipose tissue in the inhalation group were lower than in the oral administration group. Long-term (50 days) inhalation to volatile turmerones suppressed weight gain and hypertrophy of adipocytes in the epididymal fat of mice fed a high-fat diet. These results suggest that inhaled turmerones can be incorporated into the organs of mice via different pathway from as to those from oral administration and can affect the biological function of the organs under certain conditions.
... Foci of bleeding (defined as spots/mm 3 ) were ~100-fold greater in the OB than the brain. For these calculations, the size of mouse OB was assumed to be ~2% of the brain by volume (McGann, 2017). The elevated bleeding in the OB is consistent with the fact that VSV is most abundant in this brain region following intranasal inoculation. ...
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Central nervous system (CNS) infections are a major cause of human morbidity and mortality worldwide. Even patients that survive CNS infections can have lasting neurological dysfunction resulting from immune and pathogen induced pathology. Developing approaches to noninvasively track pathology and immunity in the infected CNS is crucial for patient management and development of new therapeutics. Here, we develop novel MRI-based approaches to monitor virus-specific CD8+ T cells and their relationship to cerebrovascular pathology in the living brain. We studied a relevant murine model in which a neurotropic virus (vesicular stomatitis virus) was introduced intranasally and then entered the brain via olfactory sensory neurons - a route exploited by many pathogens in humans. Using T2*-weighted high-resolution MRI, we identified small cerebral microbleeds as an early form of pathology associated with viral entry into the brain. Mechanistically, these microbleeds occurred in the absence of peripheral immune cells and were associated with infection of vascular endothelial cells. We monitored the adaptive response to this infection by developing methods to iron label and track individual virus specific CD8+ T cells by MRI. Transferred antiviral T cells were detected in the brain within a day of infection and were able to reduce cerebral microbleeds. These data demonstrate the utility of MRI in detecting the earliest pathological events in the virally infected CNS as well as the therapeutic potential of antiviral T cells in mitigating this pathology.
... Flavor evokes a unitary percept, despite originating from the contributions of three sensory modalities. Chemosensory perception is enriched by information from other sensory modalities, memory, and cognition (see e.g., Gottfried et al. (2004), ), but it also plays a crucial role in emotion regulation (e.g., Kontaris et al., 2020), social interaction (e.g., Lübke and Pause, 2015), nutrition, and overall well-being (e.g., McGann, 2017;Boesveldt and Parma, 2021). Functional connectome studies further help us to understand the central processing of chemosensory signals. ...
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Ecological chemosensory stimuli almost always evoke responses in more than one sensory system. Moreover, any sensory processing takes place along a hierarchy of brain regions. So far, the field of chemosensory neuroimaging is dominated by studies that examine the role of brain regions in isolation. However, to completely understand neural processing of chemosensation, we must also examine interactions between regions. In general, the use of connectivity methods has increased in the neuroimaging field, providing important insights to physical sensory processing, such as vision, audition, and touch. A similar trend has been observed in chemosensory neuroimaging, however, these established techniques have largely not been rigorously applied to imaging studies on the chemical senses, leaving network insights overlooked. In this article, we first highlight some recent work in chemosensory connectomics and we summarize different connectomics techniques. Then, we outline specific challenges for chemosensory connectome neuroimaging studies. Finally, we review best practices from the general connectomics and neuroimaging fields. We recommend future studies to develop or use the following methods we perceive as key to improve chemosensory connectomics: (1) optimized study designs, (2) reporting guidelines, (3) consensus on brain parcellations, (4) consortium research, and (5) data sharing.
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The human sense of smell plays an important role in appetite and food intake, detecting environmental threats, social interactions, and memory processing. However, little is known about the neural circuity supporting its function. The olfactory tracts project from the olfactory bulb along the base of the frontal cortex, branching into several striae to meet diverse cortical regions. Historically, using diffusion magnetic resonance imaging (dMRI) to reconstruct the human olfactory tracts has been prevented by susceptibility and motion artifacts. Here, we used a dMRI method with readout segmentation of long variable echo-trains (RESOLVE) to minimize image distortions and characterize the human olfactory tracts in vivo We collected high-resolution dMRI data from 25 healthy human participants (12 male and 13 female) and performed probabilistic tractography using constrained spherical deconvolution (CSD). At the individual subject level, we identified the lateral, medial, and intermediate striae with their respective cortical connections to the piriform cortex and amygdala (AMY), olfactory tubercle (OT), and anterior olfactory nucleus (AON). We combined individual results across subjects to create a normalized, probabilistic atlas of the olfactory tracts. We then investigated the relationship between olfactory perceptual scores and measures of white matter integrity, including mean diffusivity (MD). Importantly, we found that olfactory tract MD negatively correlated with odor discrimination performance. In summary, our results provide a detailed characterization of the connectivity of the human olfactory tracts and demonstrate an association between their structural integrity and olfactory perceptual function.SIGNIFICANCE STATEMENT This study provides the first detailed in vivo description of the cortical connectivity of the three olfactory tract striae in the human brain, using diffusion magnetic resonance imaging (dMRI). Additionally, we show that tract microstructure correlates with performance on an odor discrimination task, suggesting a link between the structural integrity of the olfactory tracts and odor perception. Lastly, we generated a normalized probabilistic atlas of the olfactory tracts that may be used in future research to study its integrity in health and disease.
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Several studies report that olfactory cues play an important role in human life; humans are essentially able to recognize other family members and friends by their odors. Moreover, recent studies report that humans are also able to identify odors of non-conspecifics. The aim of this study was to determine whether dog owners are able to identify their dogs by smell and distinguish the odor of their own dogs from those of other dogs. A total of 53 dog owners (40 females and 13 males of different ages) volunteered to take part in this study. A number of the participants (17) owned 2 dogs; these owners took part in the study twice (i.e., working with only one dog at a time). Sterile gauze pads were used to collect odor samples from the dogs. Each pad was placed in its own sterile glass jar (750 ml) with a twist off lid until the experiment commenced. Participants were asked to identify their own dog´s odor from a line-up of 6 glass containers. This experiment demonstrated that dog owners are capable of identifying their dogs by smell on a significant level. Results of this study additionally suggested that male owners outperformed their female counterparts in the identification process. Moreover, dog owners whose dogs were housed outside had a higher success rate in identification than did participants who kept their dogs indoors with them. The dog owners found it easier to identify dogs that had been neutered, fed dry dog food and bathed less frequently. In general, younger dog owners tended to have more success when attempting to identify their dogs than did their older counterparts.
Article
Androstenol has been reported to influence judgements of attractiveness and to affect participants’ mood. In the present study, participants were asked to sniff androstenol or a control odour (pure ethanol) unilaterally with the left or right nostril. Subsequently, they rated the attractiveness of photographs of the opposite sex and their own feelings on four mood scales. Participants rated the photographs as significantly more attractive after sniffing androstenol compared with the control odour. This did not depend upon androstenol being perceived as pleasant. Androstenol made male participants feel more lively, and both male and female participants more sexy, when sniffed through the right compared with the left nostril. Participants rated themselves as more irritable and aggressive when exposed to androstenol through the left nostril. The findings are discussed in relation to the effects of arousal on attraction and in the context of current theories of hemispheric differences in emotion.
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Olfaction could influence how people respond to threats or select a partner. To investigate, researchers need to design experiments that can capture its effects. Olfaction could influence how people respond to threats or select a partner. To investigate, researchers need to design experiments that can capture its effects.
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Background The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected over 100 million people causing over 2.4 million deaths over the world, and it is still expanding. Although, ACE2 has been identified as the principal host cell receptor of 2019-nCoV, and it is thought to play a critical role in the virus's entrance into the cell and subsequent infection, many cells can be infected by COVID-19 while also expressing little or no ACE2. Unlike other viral infections, COVID-19 is characterized by widespread and severe systemic manifestations, immune dysregulation and multi-organ involvement. In addition, the range of serious inflammatory, neuropsychiatric and autoimmune diseases called post-COVID syndromes are now left behind as disease tables. This wide and diverse spectrum of diseases seen in COVID-19 cannot be explained by the mechanism of viral tropism mediated by ACE2 and TMPRSS2 receptors. It is possible that different receptor and signaling mechanisms that cannot be explained by the viral tropism mechanism play a role in the pathogenesis of acute systemic effects and chronic post-COVID syndromes in COVID-19. It was showed that COVID-19 infection leads to a loss of smell (anosmia) but the COVID-19 entry receptors, angiotensin-converting enzyme 2 (ACE2), is not expressed in the receptor of olfactory neurons, or its generation is limited to a minor fraction of these neurons. Moreover It was demonstrated that COVID-19 could infect lymphocyte through its ACE2 receptors, but numerous studies found that lymphocytes don't express ACE2 receptors or express it with a little, insufficient amount. It is clear from the information and findings presented and addressed in our article that COVID-19 not only binds to ACE2, but also to additional receptors, leading to more disease lethality and existence of covid-19 symptoms which remain unexplained. As a result, discovering and identifying these receptors could lead to the development of new treatments that could suppress COVID-19 and reduce its severity and pathogenicity. Herein, we insilico discovered that blocking of STRA6 by the SARS-CoV-2 spike protein could disrupt the retinoid signaling mechanism and leads to pathogenetic consequences through some other inflammatory pathways. Methods The STRA6 receptor protein were submitted to the server for functional interaction associated network between partners for the STRING (Research Online of Interacting Genes/Proteins Data Basis version 10.0)13 .Docking study of each Spike -ACE 2 and STRA6 receptor protein were carried out using HDOCK server (http://hdock.phys.hust.edu.cn/). The binding mode of Spike -ACE 2 and STRA6 receptor protein is retrieved form the PDB https://www.rcsb.org/ with accession number (7DMU , 5sy1) Results Our results showed that COVID-19 Spike protein exhibited a high binding affinity for human STRA6 and a low binding energy with it. The docking score of COVID-19 spike protein with STRA6( -354.68) kcal/mol was higher than the docking score of spike protein with ACE2 (-341.21 ) kcal/mol. Spike protein Receptor Binding Domain(RDB) of COVID-19 strongly and efficiently binds to STRA6 receptor, definitely to the RDB vital residues of RBP-binding motif located in STRA6 receptor. The docking of STRA6 target protein with spike viral protein revealed the involvement of the spike protein into the extracellular and membrane part of the STRA6 receptor and amino acids residues of STRA6 along with spike protein which make interactions and play an important role in formation of complexes. The corresponding distances about the residue contacts between proteins STRA6- Spike protein complex are documented here where the STRA6- Spike protein complexes binding site are the RDB of the CHOLESTEROL in STRA6 receptor which bind with interface residue( ARG 511A , VAL 512A THR 515A ALA 516A ASN 519A with interface residue degree (2.965 , 3.595 , 3.286 , 4.592 , and 4.235) representatively, also the ability of the spike to bind to RDB of the STRA 6 protein in the ILE 131C , MET 145C , HIS 86A with interface residue( 4.961 , 4.953 and 3.271) representatively. STRA6- Spike protein complex with PDB ID (5SY1 , 6LZG). Conclusions STRA6 is a critical regulator of many biological processes thorough initiating cellular retinol uptake, in different organs and tissues as in immune cells for improving the immune system homeostasis in various populations. Our docking study reveals that COVID-19 spike protein binds directly to the integral membrane receptor (STRA6) in addition to its binding sites of the cholesterol. STRA6 mediates cellular uptake of retinol (vitamin A) by recognizing a molecule of RBP-retinol to trigger release and internalization of retinol . Therefore COVID-19 may leads to downregulation of STRA6 receptor leading to inhibition the regulatory function of retinoic acid and cholesterol helping in existing symptoms and complications including lymhopenia, Nuerogical disorders, Ineffective RIG-I pathway, Interferon inhibition, Cytokine storm, Diabetes, Hormonal imbalance, Thrombosis, and Smell loss. Therefore, we believe that this novel discovery that STRA6 receptor acts as a novel binding receptor for COVID-19 could explain COVID-19 severity and its common symptoms with unknown aetiology . Moreover, retinoic acid metabolism was found to be defective in COVID-19 (cytokine storm), sepsis, ARDS and SIRS .As a result reconstitution of the retinoid signaling may prove to be a valid strategy for COVID-19 management. We suggest that Vitamin A metabolites ,especially, retinoic acid will be promising and effective treatments for COVID-19 infection and its unknown aetiology symptoms. It worth mentioning that aerosolized all- trans retinoic acid and 13 cis retinoic acid is currently under clinical investigation (ClinicalTrials.gov Identifier: NCT05002530, NCT04353180)
Thesis
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Odor perception is an essential function in humans, allowing for hazard prevention, food detection and social communication. However, this sense is often underestimated, especially regarding the ability to identify and describe odors through language. In this PhD, we aimed to better understand the subjective experience of smell, its diversity, and its neural correlates. To this end, we first introduced olfaction with its specificities and the importance of hedonics in odor perception. Then, we investigated interindividual variability in olfaction through a series of studies and showed that olfactory perception comprises both a shared and a diverse component depending on the odorants, with little effect of common factors of variation like age or sex. Also, we showed that the relation between chemical structure, receptors and perception of odors is influenced by the degree of interindividual variability, a finding important for the ongoing stimulus-percept issue in olfactory research. Through this bibliographic and experimental work, we show that there is a lack of reflection on the way we measure perception, and that its subjective nature has been under considered in contemporary research. We thus discuss the place of subjectivity in science and several methodologies that were proposed to better integrate first-person reports in experimental protocols. From these approaches, we set up a new study collecting unbiased subjective reports of odors, to construct a descriptive model of olfactory experience. We found that contrary to common belief, people can talk about odors, using references to diverse categories, including associated memories, qualitative description, source, impact, use and difficulty. With data mining, we were also able to get a fine-grained characterization a few perceptual profiles for the odors. Next, we considered the ongoing debate around the neural basis of consciousness, and the proposed methodologies to relate first-person data with cerebral activity measurements. Another study thus attempted to relate the subjective experience of odors with the evoked brain activity. The results open new ways to construct imaging protocols with a better inclusion of first-person accounts. In conclusion, we argue that subjective data has an important place in experimental research that it must be rigorously collected to fully understand human perception. We also emphasize the importance of integrating different disciplinary approaches to get a global picture of our objects of study.
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In recent decades, the trend or the need for an experience of the effect of immersion into theatre events, other branches of art, tourism, everyday business and private life has become quite evident. We are used to audio-visual communication, which, from the Renaissance onwards, became the dominant channel for delivering messages, while other senses became less important. Until the middle of the 20th century, the role of smell in theatre practices was neglected, and more important senses took over the place of communication and staging. Rarely it was used as a direct prop, but always very carefully, because, according to many experts, it cannot be controlled like sound and light. However, we have forgotten that the smell, especially in combination with the sound, can have a strong emotional impact on a spectator. Like the other senses, the scent recreates the context of memories and can evoke an intense reliving of emotions and events. It can also provoke an evaluation or re-evaluation of the past, thereby affecting the perception of the present. Reality is perceived through the adaptation of sensory information, which is shaped and interpreted under the influence of past experiences. Experiences create expectations, and expectations create our subjective reality considering everyday life and theatrical performance. This relationship is especially noticeable in sensorial theatre. In the last decade, an effort has been made to bring scents and other tools of sensorial theatre back to the stage, just as – according to foreign sources – they were an important part of events in antiquity. In this way, the stage can be enriched with an additional dimension of communication and expression. The paper presents various methods and experiments on the use of scent and other tools of sensorial theatre, evaluating their phenomenology and effectiveness from the perspective of the performing arts and psychological science.
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During two retreats in 2017 and 2020, a group of international scientists convened to explore the Human-Animal Bond. The meetings, hosted by the Wallis Annenberg PetSpace Leadership Institute, took a broad view of the human-dog relationship and how interactions between the two may benefit us medically, psychologically or through their service as working dogs (e.g. guide dogs, explosive detection, search and rescue, cancer detection). This Frontiers’ Special Topic has collated the presentations into a broad collection of 14 theoretical and review papers summarizing the latest research and practice in the historical development of our deepening bond with dogs, the physiological and psychological changes that occur during human-dog interactions (to both humans and dogs) as well as the selection, training and welfare of companion animals and working dogs. The overarching goals of this collection are to contribute to the current standard of understanding of human-animal interaction, suggest future directions in applied research, and to consider the interdisciplinary societal implications of the findings.
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Problem imenovanja ni kateri koli filozofski problem, pač pa je osrednjega pomena za klasično ontologijo, ki se opira na koncept imen (onomata) kot oprijemajočih se reči (pragmata) v njihovi bistveni biti. Kot tako je bilo ime tradicionalno zvezano s konceptom resnice kot adequatio, tj. resnice kot ujemanja med vednostjo in bitjo, intelektom in rečjo ali propozicijo in realnostjo. Na tem mestu bomo vrgli pogled s strani na ta masivni filozofski problem, tako da se ga bomo lotili s posebnega vidika vonjav in njihovega osupljivega razmerja do jezika.
Chapter
Even though the human sense of smell provides critical information for one’s health and well-being, it is still often considered a vestigial sense, and, as a result, it does not receive the attention necessary to avoid negative clinical outcomes. Appropriately investigating the sense of smell allows us to identify early indicators for the presence of disease, as well as mapping the course of disease. Here, we review screening and assessment measures that can be used to investigate the sense of smell, provide an analysis of pros and cons in different situations, and report the clinical scenarios in which the tests have been used. We argue for the use of smell testing in routine clinical practice across developmental stages, in particular using cost-effective, and time-sensitive methods.
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Decomposition in seafood products in the United States is monitored by the Food and Drug Administration (FDA) laboratories using sensory testing, which requires highly trained analysts. A large‐volume headspace (LVHS) gas chromatography/mass spectrometry (GC/MS) method was developed to generate analytical results that can be directly compared to sensory evaluation. Headspace vapor was withdrawn from a 1‐L vial containing 50 g seafood sample using a large volume headspace autosampler. Various volatile compounds were collected simultaneously. Analytes were preconcentrated by a capillary column trapping system and then sent through a cryo‐focuser mounted onto the GC injector. A selected ion monitoring (SIM) MS acquisition method was used to selectively monitor 38 compounds of interest. Samples of red snapper, croaker, weakfish, mahi‐mahi, black tiger shrimp, yellowfin tuna, and sockeye salmon that have been assessed and scored by an FDA National Seafood Sensory Expert (NSSE) were used for method performance evaluation. Characteristic compounds potentially associated with seafood quality deterioration for each seafood species were identified by quantitative analysis using pooled matrix‐matched calibrations and two‐sample t‐test statistical analysis. Classification of fresh and decomposed samples was visualized on the analysis of variance (ANOVA)–principal component analysis (PCA) score plots. The results determined that the LVHS‐GC/MS technique appeared promising as a screening tool to identify compounds representative of sensory analysis. Large volume headspace GC/MS generated analytical results that can be directly compared to sensory evaluation. Classification of fresh and decomposed seafood samples was successful. VOCs relating to seafood decomposition were identified.
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Recognition of olfactory-induced electroencephalogram (EEG) signals can provide an effective means for the research on disorder diagnostics and human–machine interaction. A novel triangular hashing (TH) approach is proposed for EEG signal recognition. The TH approach consists of a triangular feature construction and a hash inspired coding idea, which makes effective use of the feature differences between EEG electrodes. Firstly, a triangular feature set with N layers is constructed based on power-spectral density (PSD) features extracted from N electrodes for each frequency band of each olfactory EEG sample. Subsequently, the electrode orders, i.e. the TH codes for each layer of the constructed feature set are obtained by arranging the feature values in ascending order. Finally, the prediction type of the testing sample is determined by finding the most similar TH codes between EEG types and the testing sample. Experimental results reveal that for the recognition of olfactory EEG signals acquired from eleven subjects, the proposed TH recognition approach yields the considerably high accuracy of 93.0%, significantly superior to the other eight traditional methods. Besides, the EEG dataset with 5005 samples used in this study is made public through the website presented in this paper. In this way, the proposed TH method combined with the published EEG dataset may provide new perspectives for further study in olfactory EEG research.
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Silver fir trees have cycles of low and high seed production, and thus it is necessary to collect seeds in high production years to save them for low production years to ensure the continuity of nursery production. Tree seeds can be stored loosely in piles or containers, but they need to be checked for viability before planting. The objective of this study was to find a quick and inexpensive method to determine the suitability of seed lots for planting. The working hypothesis was that an electronic nose device could be used to detect odors from fungi or from decomposing organic material, and thus aid in determination of whether seeds could be sown or discarded. To affirm and supplement results from the electronic nose, we used gas chromatography–mass spectrometry (GC-MS) to detect volatile secondary metabolites such as limonene and cadienes, which were found at the highest concentrations in both, infected and uninfected seeds. Uninfected seeds contained exceptionally high concentrations of pinene, which are known to be involved in plant resistance responses. Statistically higher levels of terpineol were found in infected seeds than in uninfected seeds. A prototype of our electronic nose partially discriminated between healthy and spoiled seeds, and between green and white fungal colonies grown on incubated seeds. These preliminary observations were encouraging and we plan to develop a practical device that will be useful for forestry and horticulture.
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Background Olfaction is a versatile sensory mechanism for detecting thousands of volatile odorants. Although molecular basis of odorant signaling is relatively well understood considerable gaps remain in the complete charting of all relevant gene products. To address this challenge, we applied RNAseq to four well-characterized human olfactory epithelial samples and compared the results to novel and published mouse olfactory epithelium as well as 16 human control tissues. ResultsWe identified 194 non-olfactory receptor (OR) genes that are overexpressed in human olfactory tissues vs. controls. The highest overexpression is seen for lipocalins and bactericidal/permeability-increasing (BPI)-fold proteins, which in other species include secreted odorant carriers. Mouse-human discordance in orthologous lipocalin expression suggests different mammalian evolutionary paths in this family.Of the overexpressed genes 36 have documented olfactory function while for 158 there is little or no previous such functional evidence. The latter group includes GPCRs, neuropeptides, solute carriers, transcription factors and biotransformation enzymes. Many of them may be indirectly implicated in sensory function, and ~70 % are over expressed also in mouse olfactory epithelium, corroborating their olfactory role.Nearly 90 % of the intact OR repertoire, and ~60 % of the OR pseudogenes are expressed in the olfactory epithelium, with the latter showing a 3-fold lower expression. ORs transcription levels show a 1000-fold inter-paralog variation, as well as significant inter-individual differences. We assembled 160 transcripts representing 100 intact OR genes. These include 1–4 short 5’ non-coding exons with considerable alternative splicing and long last exons that contain the coding region and 3’ untranslated region of highly variable length. Notably, we identified 10 ORs with an intact open reading frame but with seemingly non-functional transcripts, suggesting a yet unreported OR pseudogenization mechanism. Analysis of the OR upstream regions indicated an enrichment of the homeobox family transcription factor binding sites and a consensus localization of a specific transcription factor binding site subfamily (Olf/EBF). Conclusions We provide an overview of expression levels of ORs and auxiliary genes in human olfactory epithelium. This forms a transcriptomic view of the entire OR repertoire, and reveals a large number of over-expressed uncharacterized human non-receptor genes, providing a platform for future discovery.
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Morphometric parameters of olfactory brain components show species-dependent variations. However, the association of these parameters with olfactory function vis-à-vis ecological and evolutionary behaviors is poorly understood. In this study, a morphometric analysis of the olfactory bulb, tract and stria was carried out in three ecologically diverse animals comprising humans (primate), dogs (carnivore) and goats (herbivore) to elucidate differences in morphometry in relation to olfactory function. Using formalin-fixed brains, volumes and linear measurements of the olfactory structures were determined and correlated with those of cerebrum and the whole brain. The volume of the olfactory bulb was greatest in dogs, followed by goats and humans and constituted 0.31%, 0.18% and 0.01%, respectively, of the brain volume. Similarly, the ratio of volume of the bulb, tract and stria to that of brain was 1.95% in the dog, 0.77% in the goat and 0.03% in the human. The width of the bulb was greatest (p< 0.05) in dogs (10.80±1.64 mm) compared to goats (8.25±0.96 mm) and humans (5.50±0.71 mm), and accounted for a hemisphere breadth of 42.91%, 29.73% and 8.94% respectively. Interestingly though, the total length of the olfactory bulb, tract and striae increased in the order of goat (34.5±1.30 mm), human (36.25±1.70 mm) and dog (48.20±1.92 mm), and constituted 21.47%, 51.87% and 72.30%, respectively, of the hemisphere length. These results suggest that the morphometric adaptations of the olfactory components to olfactory function decline from the dog,to goat, to human, and this may be indicative of the varied olfactory functional needs in regard to the ecological diversity of these species.
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Effects of smells on stress have been demonstrated in animals and humans, suggesting that inhaling certain odorants may counteract the negative effects of stress. Because stress plays a key role in cerebral aging, the present study set out to examine whether positive odor effects on perceived stress can be achieved in elderly individuals. To this end, two groups of aged individuals (n = 36 women, aged from 55 to 65 years), were tested. The first group was exposed for 5 days to a pleasant and, by end of exposure, familiar odor ("exposure odor"), whereas the other was exposed to a non-scented control stimulus. Stress and mood states were assessed before and after the 5-day odor exposure period. Psychophysiological markers were also assessed at the end of exposure, in response to the "exposure odor" and to a "new odor." Results revealed that stress on this second exposure was decreased and zygomatic electromyogram activity was increased specifically in the group previously exposed to the odor (p < 0.05). Taken as a whole, these findings offer a new look at the relationship between perceived stress, olfaction and normal aging, opening up new research perspectives on the effect of olfaction on quality of life and well-being in aged individuals.
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Why we like or dislike certain products may be better captured by physiological and behavioral measures of the autonomic nervous system (ANS) than by conscious or classical sensory tests. Responses to pleasant and unpleasant food odors presented in varying concentrations were assessed continuously using facial expressions and responses of the ANS. Results of 26 young and healthy female participants showed that the unpleasant fish odor triggered higher heart rates and skin conductance responses, lower skin temperature, fewer neutral facial expressions and more disgusted and angry expressions (p < 0.05). Neutral facial expressions differentiated between odors within 100 ms, after the start of the odor presentation followed by expressions of disgust (180 ms), anger (500 ms), surprised (580 ms), sadness (820 ms), scared (1020 ms), and happy (1780 ms) (all p-values < 0.05). Heart rate differentiated between odors after 400 ms, whereas skin conductance responses differentiated between odors after 3920 ms. At shorter intervals (between 520 and 1000 ms and between 2690 and 3880 ms) skin temperature for fish was higher than that for orange, but became considerable lower after 5440 ms. This temporal unfolding of emotions in reactions to odors, as seen in facial expressions and physiological measurements supports sequential appraisal theories.
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In applied olfactory cognition the effects that olfactory stimulation can have on (human) behavior are investigated. To enable an efficient application of olfactory stimuli a model of how they may lead to a change in behavior is proposed. To this end we use the concept of olfactory priming. Olfactory priming may prompt a special view on priming as the olfactory sense has some unique properties which make odors special types of primes. Examples of such properties are the ability of odors to influence our behavior outside of awareness, to lead to strong affective evaluations, to evoke specific memories, and to associate easily and quickly to other environmental stimuli. Opportunities and limitations for using odors as primes are related to these properties, and alternative explanations for reported findings are offered. Implications for olfactory semantic, construal, behavior and goal priming are given based on a brief overview of the priming literature from social psychology and from olfactory perception science. We end by formulating recommendations and ideas for a future research agenda and applications for olfactory priming.
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The central nervous system rapidly learns that particular stimuli predict imminent danger. This learning is thought to involve associations between neutral and harmful stimuli in cortical and limbic brain regions, though associative neuroplasticity in sensory structures is increasingly appreciated. We observed the synaptic output of olfactory sensory neurons (OSNs) in individual mice before and after they learned that a particular odor indicated an impending foot shock. OSNs are the first cells in the olfactory system, physically contacting the odor molecules in the nose and projecting their axons to the brain's olfactory bulb. OSN output evoked by the shock-predictive odor was selectively facilitated after fear conditioning. These results indicate that affective information about a stimulus can be encoded in its very earliest representation in the nervous system.
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In the last years, an increasing interest has been paid to the olfactory system, particularly to its abilities of plasticity and its potential continuous neurogenesis throughout adult life. Although mechanisms underlying adult neurogenesis have been largely investigated in animals, to some degree they remain unclear in humans. Based on human research findings, the present review will focus on the olfactory bulb as an evidence of the astonishing plasticity of the human olfactory system.
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Long-term plasticity in sensory systems is usually conceptualized as changing the interpretation of the brain of sensory information, not an alteration of how the sensor itself responds to external stimuli. However, here we demonstrate that, in the adult mouse olfactory system, a 1-week-long exposure to an artificially odorized environment narrows the range of odorants that can induce neurotransmitter release from olfactory sensory neurons (OSNs) and reduces the total transmitter release from responsive neurons. In animals heterozygous for the olfactory marker protein (OMP), this adaptive plasticity was strongest in the populations of OSNs that originally responded to the exposure odorant (an ester) and also observed in the responses to a similar odorant (another ester) but had no effect on the responses to odorants dissimilar to the exposure odorant (a ketone and an aldehyde). In contrast, in OMP knock-out mice, odorant exposure reduced the number and amplitude of OSN responses evoked by all four types of odorants equally. The effect of this plasticity is to preferentially sparsen the primary neural representations of common olfactory stimuli, which has the computational benefit of increasing the number of distinct sensory patterns that could be represented in the circuit and might thus underlie the improvements in olfactory discrimination often observed after odorant exposure (Mandairon et al., 2006a). The absence of odorant specificity in this adaptive plasticity in OMP knock-out mice suggests a potential role for this protein in adaptively reshaping OSN responses to function in different environments.
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In many animal species, social communication and mate choice are influenced by cues encoded by the major histocompatibility complex (MHC). The mechanism by which the MHC influences sexual selection is a matter of intense debate. In mice, peptide ligands of MHC molecules activate subsets of vomeronasal and olfactory sensory neurons and influence social memory formation; in sticklebacks, such peptides predictably modify the outcome of mate choice. Here, we examine whether this evolutionarily conserved mechanism of interindividual communication extends to humans. In psychometric tests, volunteers recognized the supplementation of their body odour by MHC peptides and preferred 'self' to 'non-self' ligands when asked to decide whether the modified odour smelled 'like themselves' or 'like their favourite perfume'. Functional magnetic resonance imaging indicated that 'self'-peptides specifically activated a region in the right middle frontal cortex. Our results suggest that despite the absence of a vomeronasal organ, humans have the ability to detect and evaluate MHC peptides in body odour. This may provide a basis for the sensory evaluation of potential partners during human mate choice.
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Increased sensitivity to specific cues in the environment is common in anxiety disorders. This increase in sensory processing can emerge through attention processes that enhance discrimination of a cue from other cues as well as through augmented senses that reduce the absolute intensity of sensory stimulation needed for detection. Whereas it has been established that aversive conditioning can enhance odor quality discrimination, it is not known whether it also changes the absolute threshold at which an odor can be detected. In two separate experiments, we paired one odor of an indistinguishable odor pair with an aversive outcome using a classical conditioning paradigm. Ability to discriminate and to detect the paired odor was assessed before and after conditioning. The results demonstrate that aversive conditioning increases absolute sensory sensitivity to a predictive odor cue in an odor-specific manner, rendering the conditioned odor detectable at a significantly lower (20%) absolute concentration. As animal research has found long-lasting change in behavior and neural signaling resulting from conditioning, absolute threshold was also tested eight weeks later. Detection threshold had returned to baseline level at the eight week follow-up session suggesting that the change in detection threshold was mediated by a transient reorganization. Taken together, we can for the first time demonstrate that increasing the biological salience of a stimulus augments the individual's absolute sensitivity in a stimulus-specific manner outside conscious awareness. These findings provide a unique framework for understanding sensory mechanisms in anxiety disorders as well as further our understanding of mechanisms underlying classical conditioning.
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In this Chapter the abilities of humans and animals to detect odorants and to perceive the strengths of suprathreshold concentrations of odorants are compared and an effort is made to provide conceptual and practical reasons for such comparisons. In addition, current obstacles to more profitable use of psychophysical data for determining the neural mechanisms that underlie human odor perception are discussed. Results from odor psychophysical experiments in humans and animals are then summarized and general conclusions and recommendations for future research are offered.