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"Olfactory Perception - physiology"
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Chemistry and the sense of smell
\"I cannot recommend this fascinating book highly enough.\" –Simon Cotton, Chemistry & Industry, September 2014
\"In conclusion: A comprehensive introduction to the world of odours, not only for chemists.\" –review in German: Monika Paduch, Gefahrstoffe - Reinhaltung Luft, October 2014 A comprehensive overview of fragrance chemistry
Fragrance materials are universal, from personal care products to household cleaners, laundry products, and more. Although many of the scents themselves are synthesized in a lab, the actual mechanism of odour has long baffled chemists who attempt to model it for research. In Chemistry and the Sense of Smell, industry chemist Charles S. Sell explores the chemistry and biology surrounding the human detection and processing of odour, providing a comprehensive, single-volume guide to the totality of fragrance chemistry.
The correlation between molecular structure and odour is much more complex than initially thought, and the intricacies of the mechanism by which the brain interprets scent signals leaves much to be discovered. This book provides a solid foundation of fragrance chemistry and highlights the relationship between research and industry with topics such as:
* The analysis and characterization of odour
* The role scent plays in our lives
* The design and manufacture of new fragrance ingredients
* The relationship between molecular structure and odour
* The mechanism of olfaction
* Intellectual challenges and the future of the field
Complete with illustrations that clarify difficult concepts and the structures of the molecules under discussion, Chemistry and the Sense of Smell is an all-inclusive guide to the science of scent. For professionals in the fragrance industry or related fields, this book is one resource that should not be overlooked.
eBook
Olfactory Training in Patients with Parkinson's Disease
Decrease of olfactory function in Parkinson's disease (PD) is a well-investigated fact. Studies indicate that pharmacological treatment of PD fails to restore olfactory function in PD patients. The aim of this investigation was whether patients with PD would benefit from \"training\" with odors in terms of an improvement of their general olfactory function. It has been hypothesized that olfactory training should produce both an improved sensitivity towards the odors used in the training process and an overall increase of olfactory function.
We recruited 70 subjects with PD and olfactory loss into this single-center, prospective, controlled non-blinded study. Thirty-five patients were assigned to the olfactory training group and 35 subjects to the control group (no training). Olfactory training was performed over a period of 12 weeks while patients exposed themselves twice daily to four odors (phenyl ethyl alcohol: rose, eucalyptol: eucalyptus, citronellal: lemon, and eugenol: cloves). Olfactory testing was performed before and after training using the \"Sniffin' Sticks\" (thresholds for phenyl ethyl alcohol, tests for odor discrimination, and odor identification) in addition to threshold tests for the odors used in the training process.
Compared to baseline, trained PD patients experienced a significant increase in their olfactory function, which was observed for the Sniffin' Sticks test score and for thresholds for the odors used in the training process. Olfactory function was unchanged in PD patients who did not perform olfactory training.
The present results indicate that olfactory training may increase olfactory sensitivity in PD patients.
Journal Article
Insulin Resistance Is Associated with Reduced Food Odor Sensitivity across a Wide Range of Body Weights
The worldwide obesity epidemic is a major health problem driven by the modern food environment. Recently, it has been shown that smell perception plays a key role in eating behavior and is altered in obesity. However, the underlying mechanisms of this phenomenon are not well understood yet. Since the olfactory system is closely linked to the endocrine system, we hypothesized that hormonal shifts in obesity might explain this relationship. In a within-subject, repeated-measures design, we investigated sensitivity to a food and a non-food odor in the hungry and sated state in 75 young healthy (26 normal weight, 25 overweight, and 24 obese) participants (37 women). To determine metabolic health status and hormonal reactivity in response to food intake, we assessed pre- and postprandial levels of insulin, leptin, glucose, and ghrelin. Odor sensitivity did not directly depend on body weight status/body mass index (BMI) or hunger state. However, we could establish a strong negative mediating effect of insulin resistance on the relationship between BMI/waist-hip ratio and olfactory sensitivity for the food odor. These findings indicate an impact of metabolic health status on sensitivity to food odors. Our results contribute to a better understanding of the mechanisms behind altered smell perception in obesity.
Journal Article
Correlation between olfactory bulb volume and olfactory function in children and adolescents
The olfactory bulb (OB) is considered to be the most important relay station in odor processing. The present study aimed to investigate the volumetric development of the human bulb and the olfactory function during childhood and youth. Furthermore, the present study aimed to investigate a possible correlation between OB volume and specific olfactory functions including odor threshold, odor discrimination and odor identification. A total of 87 subjects (46 boys, 41 girls), aged 1–17 years (mean age 8 years), participated in this study. None of them reported olfactory dysfunction or had signs of a dysfunctional sense of smell. Whenever possible, participants received a volumetric scan of the brain and lateralized olfactory tests. Volumetric measurements of the right and left OB were taken by manual segmentation of the coronal slices through the OB. Significant correlations between OB volumes and olfactory function were observed. Both, OB volumes and olfactory function increased with age, although the correlation between structure and function was not mediated by the subjects’ age. In conclusion, for the first time, the present study showed a correlation between OB volume and olfactory functions in children.
Journal Article
Subjective Effects of Inhaling Kuromoji Tea Aroma
Teas and various herbal teas are well-known beverages and are commonly consumed around the world. In this study, we focused on kuromoji tea. Kuromoji is a deciduous shrub of the Lauraceae family, and the plucked leaves and branches have been drunk as a tea in production areas for a long time. However, no studies have investigated the subjective and physiological effects of kuromoji tea. In this study, the effects of kuromoji tea were examined on the basis of the measurements of heart rate variability and cerebral blood flow, core body temperature and subjective assessments. Moreover, the results of this study showed that a pleasant subjective feeling could be obtained by sniffing the aroma of kuromoji teas, especially tea leaves. It was also found that the aroma of kuromoji teas has the potential to stimulate saliva secretion and increase subjective and physiological excitements in the oral cavity. 1,8-Cineole, linalool, terpinen-4-ol, carvone and geraniol were determined in both kuromoji leaves and branches. In this study, the beneficial effects of kuromoji teas when drunk conventionally were investigated.
Journal Article
Reading first or smelling first? Effects of presentation order on odor identification
Verbal labels are potent manipulators for olfactory perception, and verbal descriptors used in a cued olfactory identification test will influence the testing results. The main aim of the present study was to test whether the order of presentation of the odorants and the corresponding set of labels (verbal descriptors with or without pictures) would influence the results of a psychophysical odor identification test in 100 normosmic subjects (49 women and 51 men) and 100 patients with olfactory dysfunction (61 women and 39 men). Additionally, we investigated whether the scores would be different between subjects identifying odors from a list of verbal descriptors and subjects using both pictures and verbal descriptors. The subjects were examined with the extended, 32-item “Sniffin’ Sticks” identification test. We found that the scores of normosmic subjects were significantly higher when the subjects were presented with label options prior to smelling, whereas for patients the scores in the two conditions did not differ. Moreover, in both groups the scores were not significantly different when the subjects were presented either with verbal descriptors only or with verbal descriptors and pictures. Our findings seem to be of importance not only to research involving psychophysical olfactory identification tests or in a clinical context, but also to further experiments investigating human olfaction and cognition.
Journal Article
Family history of alcoholism mediates the frontal response to alcoholic drink odors and alcohol in at-risk drinkers
Although a family history of alcoholism is the strongest risk factor for developing alcohol dependence, there are few studies of the association between familial alcoholism and the human brain's reward system activity. We used functional magnetic resonance imaging (fMRI) to determine how family history affects the brain's response to subjects' preferred alcoholic drink odors (AO) as compared to appetitive control odors (ApCO). Fourteen non-dependent heavy drinkers (HD) who were family history positive (FHP) participated, as did 12 HD who were family history negative (FHN). Subjects were imaged under both alcohol intoxication and placebo, using intravenous infusion and pharmacokinetic modeling to target a blood alcohol level of 50 mg%. Under placebo, HD-FHP had a larger medial frontal [AO>ApCO] effect than did HD-FHN. Alcohol intoxication dampened this response in the HD-FHP but potentiated it in the HD-FHN. This suggests that a family history of alcoholism and brain exposure to alcohol interact in heavy drinkers to differentially affect how the brain responds to alcohol cues.
Journal Article
Structure and flexibility in cortical representations of odour space
The cortex organizes sensory information to enable discrimination and generalization
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. As systematic representations of chemical odour space have not yet been described in the olfactory cortex, it remains unclear how odour relationships are encoded to place chemically distinct but similar odours, such as lemon and orange, into perceptual categories, such as citrus
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. Here, by combining chemoinformatics and multiphoton imaging in the mouse, we show that both the piriform cortex and its sensory inputs from the olfactory bulb represent chemical odour relationships through correlated patterns of activity. However, cortical odour codes differ from those in the bulb: cortex more strongly clusters together representations for related odours, selectively rewrites pairwise odour relationships, and better matches odour perception. The bulb-to-cortex transformation depends on the associative network originating within the piriform cortex, and can be reshaped by passive odour experience. Thus, cortex actively builds a structured representation of chemical odour space that highlights odour relationships; this representation is similar across individuals but remains plastic, suggesting a means through which the olfactory system can assign related odour cues to common and yet personalized percepts.
Both piriform cortex and its sensory inputs from the olfactory bulb represent chemical odour relationships, but cortex reshapes relational information inherited from the sensory periphery to enhance odour generalization and to reflect experience.
Journal Article
The endocannabinoid system controls food intake via olfactory processes
Hunger arouses sensory perception, eventually leading to an increase in food intake, but the underlying mechanisms remain poorly understood. We found that cannabinoid type-1 (CB1) receptors promote food intake in fasted mice by increasing odor detection. CB1 receptors were abundantly expressed on axon terminals of centrifugal cortical glutamatergic neurons that project to inhibitory granule cells of the main olfactory bulb (MOB). Local pharmacological and genetic manipulations revealed that endocannabinoids and exogenous cannabinoids increased odor detection and food intake in fasted mice by decreasing excitatory drive from olfactory cortex areas to the MOB. Consistently, cannabinoid agonists dampened in vivo optogenetically stimulated excitatory transmission in the same circuit. Our data indicate that cortical feedback projections to the MOB crucially regulate food intake via CB1 receptor signaling, linking the feeling of hunger to stronger odor processing. Thus, CB1 receptor-dependent control of cortical feedback projections in olfactory circuits couples internal states to perception and behavior.
Journal Article