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Anatomical Record (Hoboken, N.J. : 2007) Nov 2014The importance of chemosensation for vertebrates is reflected in the vast and variable nature of their chemosensory tissues, neurons, and genes, which we explore in this... (Review)
Review
The importance of chemosensation for vertebrates is reflected in the vast and variable nature of their chemosensory tissues, neurons, and genes, which we explore in this review. Immense progress has been made in elucidating the molecular biology of olfaction since the discovery of the olfactory receptor genes by Buck and Axel, which eventually won the authors the Nobel Prize. In particular, research linking odor ligands to olfactory receptors (ORs) is truly revolutionizing our understanding of how a large but limited number of chemosensory receptors can allow us to perceive the massive diversity of odors in our habitat. This research is providing insight into the evolution of genomes and providing the raw data needed to explore links between genotype and phenotype, still a grand challenge in biology. Research into olfaction is still developing and will no doubt continue until we have a clear understanding of how all odors are detected and the evolutionary forces that have molded the chemosensory subgenome in vertebrates. This knowledge will not only be a huge step in elucidating olfactory function, advancing scientific knowledge and techniques, but there are also commercial applications for this research. This review focuses on the molecular basis of chemosensation, particularly olfaction, its evolution across vertebrates and the recent molecular advances linking odors to their cognate receptors.
Topics: Animals; Evolution, Molecular; Humans; Olfactory Receptor Neurons; Smell; Vertebrates
PubMed: 25312375
DOI: 10.1002/ar.23031 -
Sensors (Basel, Switzerland) Jan 2023A new hypothesis for the mechanism of olfaction is presented. It begins with an odorant molecule binding to an olfactory receptor. This is followed by the quantum...
A new hypothesis for the mechanism of olfaction is presented. It begins with an odorant molecule binding to an olfactory receptor. This is followed by the quantum biology event of inelastic electron tunneling as has been suggested with both the vibration and swipe card theories. It is novel in that it is not concerned with the possible effects of the tunneled electrons as has been discussed with the previous theories. Instead, the high energy state of the odorant molecule in the receptor following inelastic electron tunneling is considered. The hypothesis is that, as the high energy state decays, there is fluorescence luminescence with radiative emission of multiple photons. These photons pass through the supporting sustentacular cells and activate a set of olfactory neurons in near-simultaneous timing, which provides the temporal basis for the brain to interpret the required complex combinatorial coding as an odor. The Luminescence Hypothesis of Olfaction is the first to present the necessity of or mechanism for a 1:3 correspondence of odorant molecule to olfactory nerve activations. The mechanism provides for a consistent and reproducible time-based activation of sets of olfactory nerves correlated to an odor. The hypothesis has a biological precedent: an energy feasibility assessment is included, explaining the anosmia seen with COVID-19, and can be confirmed with existing laboratory techniques.
Topics: Humans; Smell; Luminescence; COVID-19; Olfactory Receptor Neurons; Odorants; Receptors, Odorant
PubMed: 36772376
DOI: 10.3390/s23031333 -
British Journal of Industrial Medicine Jul 1961A simple olfaction test, based on graded solutions of phenol in liquid paraffin, was examined for repeatability. Of 98 persons tested, 79 repeated their initial result...
A simple olfaction test, based on graded solutions of phenol in liquid paraffin, was examined for repeatability. Of 98 persons tested, 79 repeated their initial result to within ± one grade on a second occasion. The time interval between tests (varying from a few hours to three weeks), observers, age, smoking habits, or initial grade did not appear to affect the degree of repeatability. There was a tendency to improve the grading on the second occasion. Tests on 147 persons provided no evidence of an association between cigarette smoking and acuity of smell. There was an indication that pipe smoking had an adverse effect. An association between age and acuity was shown.
Topics: Humans; Occupational Diseases; Smell
PubMed: 13700743
DOI: 10.1136/oem.18.3.213 -
Philosophical Transactions of the Royal... Jun 2020The impact of the olfactory sense is regularly apparent across development. The fetus is bathed in amniotic fluid (AF) that conveys the mother's chemical ecology.... (Review)
Review
The impact of the olfactory sense is regularly apparent across development. The fetus is bathed in amniotic fluid (AF) that conveys the mother's chemical ecology. Transnatal olfactory continuity between the odours of AF and milk assists in the transition to nursing. At the same time, odours emanating from the mammary areas provoke appetitive responses in newborns. Odours experienced from the mother's diet during breastfeeding, and from practices such as pre-mastication, may assist in the dietary transition at weaning. In parallel, infants are attracted to and recognize their mother's odours; later, children are able to recognize other kin and peers based on their odours. Familiar odours, such as those of the mother, regulate the child's emotions, and scaffold perception and learning through non-olfactory senses. During juvenility and adolescence, individuals become more sensitive to some bodily odours, while the timing of adolescence itself has been speculated to draw from the chemical ecology of the family unit. Odours learnt early in life and within the family niche continue to influence preferences as mate choice becomes relevant. Olfaction thus appears significant in turning on, sustaining and, in cases when mother odour is altered, disturbing adaptive reciprocity between offspring and carer during the multiple transitions of development between birth and adolescence. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.
Topics: Adaptation, Biological; Adolescent; Adult; Aged; Aged, 80 and over; Child; Child, Preschool; Female; Humans; Infant; Infant, Newborn; Male; Middle Aged; Nonverbal Communication; Odorants; Olfactory Perception; Parent-Child Relations; Smell; Young Adult
PubMed: 32306879
DOI: 10.1098/rstb.2019.0261 -
Chemical Senses Jan 2023Little is known about the neural basis of lower- and higher-order olfactory functions such as odor memory, compared with other sensory systems. The aim of this study was...
Little is known about the neural basis of lower- and higher-order olfactory functions such as odor memory, compared with other sensory systems. The aim of this study was to explore neural networks and correlates associated with 3 functions: passive smelling (PS), odor encoding (OE), and in particular odor recognition memory (ORM). Twenty-six healthy participants were examined using functional magnetic resonance imaging conducted across 3 sessions, one for each function. Independent component analysis revealed a difference between sessions where a distinct ORM component incorporating hippocampus and posterior cingulate showed delayed triggering dissociated from odor stimulation and recognition. By contrasting Hit for ORM (target odors correctly recognized as old) and a combination of PS and detected odors from OE, we found significantly lower activations in amygdala, piriform cortex, insula, thalamus, and the inferior parietal lobule. Region of interest analysis including anterior insula, posterior cingulate gyrus, dentate gyrus, left middle frontal gyrus, amygdala, and piriform cortex demonstrated that Hit were associated with lower activations compared with other memory responses. In summary, our findings suggest that successful recognition of familiar odors (odor familiarity) is associated with neural suppression in the abovementioned regions of interest. Additionally, network including the hippocampus and posterior cingulate is engaged in a postrecognition process. This process may be related to incidental encoding of less familiar and more novel odors (odor novelty) and should be subject for future research.
Topics: Humans; Odorants; Smell; Recognition, Psychology; Hippocampus; Amygdala; Magnetic Resonance Imaging; Brain; Brain Mapping
PubMed: 36715106
DOI: 10.1093/chemse/bjad001 -
Proceedings of the National Academy of... Jun 2012A paradox of vertebrate brain evolution is the unexplained variability in the size of the olfactory bulb (OB), in contrast to other brain regions, which scale... (Review)
Review
A paradox of vertebrate brain evolution is the unexplained variability in the size of the olfactory bulb (OB), in contrast to other brain regions, which scale predictably with brain size. Such variability appears to be the result of selection for olfactory function, yet there is no obvious concordance that would predict the causal relationship between OB size and behavior. This discordance may derive from assuming the primary function of olfaction is odorant discrimination and acuity. If instead the primary function of olfaction is navigation, i.e., predicting odorant distributions in time and space, variability in absolute OB size could be ascribed and explained by variability in navigational demand. This olfactory spatial hypothesis offers a single functional explanation to account for patterns of olfactory system scaling in vertebrates, the primacy of olfaction in spatial navigation, even in visual specialists, and proposes an evolutionary scenario to account for the convergence in olfactory structure and function across protostomes and deuterostomes. In addition, the unique percepts of olfaction may organize odorant information in a parallel map structure. This could have served as a scaffold for the evolution of the parallel map structure of the mammalian hippocampus, and possibly the arthropod mushroom body, and offers an explanation for similar flexible spatial navigation strategies in arthropods and vertebrates.
Topics: Animals; Biological Evolution; Brain Mapping; Chemotaxis; Cognition; Humans; Olfactory Perception; Smell
PubMed: 22723365
DOI: 10.1073/pnas.1201880109 -
European Archives of... Sep 2023To determine the relationship of chemosensory screening and nasal airflow tests among the same set of participants, and to determine other factors that are related to...
PURPOSE
To determine the relationship of chemosensory screening and nasal airflow tests among the same set of participants, and to determine other factors that are related to the outcomes of these tests.
METHODS
Participants had no chemosensory complaints. Structured medical history was taken. Participants underwent 5 screening tests: q-sticks (orthonasal olfaction), q-powders (retronasal olfaction), trigeminal lateralization test, taste sprays, and peak nasal inspiratory flow (PNIF). Ratings of smell/taste ability and nasal airflow were obtained using visual analogue scales (VAS). Composite sinusitis symptoms and significance of olfaction questionnaire scores were also determined.
RESULTS
Four hundred participants were included in the study, 156 men, 244 women; aged 18-82 years (mean: 46). The q-powders and taste spray scores were weakly positively correlated with all the other chemosensory tests and PNIF. However, chemosensory test scores were not correlated with VAS, composite sinusitis symptoms, and significance of olfaction questionnaire scores. Various tests showed significant decrease starting at specific ages (in years, PNIF and trigeminal lateralization: 40, q-powders: 60, and q-sticks: 70).
CONCLUSION
Chemosensory screening tests and self-rated chemosensory function showed no correlation in participants without chemosensory complaints. In addition, gustatory function appeared to be correlated with olfactory and trigeminal function but also with nasal airflow, and nasal airflow was related not only to olfactory but also to trigeminal and taste function. Over all, the results suggest that chemosensory functions (orthonasal olfactory, trigeminal, retronasal olfactory, gustatory) and nasal airflow are correlated with each other, which we propose may be possibly mediated, at least in part, through central nervous system interactions.
Topics: Male; Humans; Female; Olfaction Disorders; Powders; Nose; Smell; Sinusitis
PubMed: 37129608
DOI: 10.1007/s00405-023-07962-6 -
Psychosomatics 2020Olfactory reference syndrome (ORS) is an underrecognized, understudied, and often severe psychiatric disorder characterized by a prominent and distressing or impairing...
BACKGROUND
Olfactory reference syndrome (ORS) is an underrecognized, understudied, and often severe psychiatric disorder characterized by a prominent and distressing or impairing preoccupation with a false belief of emitting an offensive body odor. As this condition has only recently been recognized in the International Classification of Diseases (the 11th Edition), no empirical evidence exists about the underlying features and etiology of the disorder.
OBJECTIVE
To examine the neuropsychological and olfactory functioning of individuals with ORS and address whether there is central nervous system or sensory dysfunction associated with the condition.
METHODS
In this preliminary investigation, 9 consecutive participants with ORS completed a structured clinical interview and neuropsychological and olfaction evaluations.
RESULTS
A proportion of individuals with ORS displayed deficits in aspects of cognitive functioning (i.e., processing speed, executive functioning, recognition memory bias for ORS-related words), olfaction functioning (i.e., odor detection and discrimination), and emotional processing.
CONCLUSIONS
Based on these preliminary findings of cognitive, olfaction, and emotional processing deficits in individuals with ORS, further neuropsychological and olfaction studies are needed that better characterize this understudied patient group and address this study's limitations.
Topics: Adult; Cognition; Female; Humans; Male; Middle Aged; Neuropsychological Tests; Obsessive-Compulsive Disorder; Phobia, Social; Shame; Smell; Young Adult
PubMed: 32107040
DOI: 10.1016/j.psym.2019.12.009 -
European Journal of Sport Science Feb 2023Limited research exists on athletes' olfaction. As diet is an elementary part of an athlete's lifestyle and training, it is important to know whether the sport...
Limited research exists on athletes' olfaction. As diet is an elementary part of an athlete's lifestyle and training, it is important to know whether the sport discipline itself carries a risk for olfactory impairment. The aim of this study was to evaluate whether elite swimmers (chemical irritation), boxers (head impact) or soccer players (head impact) are at risk for impaired olfaction. Elite-level male swimmers (= 30), boxers (= 35) and soccer players (= 30) aged 18-40 years were recruited from Finnish sport clubs. Floorball players (= 30) were recruited as a control group. All participants filled in a questionnaire about their training history, nasal and sinonasal diseases, asthma, nasal operations and traumas, smoking and self-evaluation of olfaction and taste function. Sniffin' Sticks odour identification test with 12 different odorants and anterior rhinoscopy were performed on all participants. The mean score from the smelling test did not differ between the sport groups. Sinonasal diseases and bronchial asthma were more common among swimmers than among the other athletes. Rhinitis symptoms were common among all athletes. Boxing, soccer or swimming does not seem to affect sense of smell. The majority of our participating elite athletes had normal olfaction, even if they had had a long history of active sports. Boxing, soccer or swimming does not seem to affect sense of smell.Rhinitis symptoms were prevalent among all elite athlete groups in our study.Athletes with hyposmia can perceive their own decreased olfaction.Swimmers have more bronchial asthma and sinus diseases than other athlete groups.
Topics: Humans; Male; Smell; Rhinitis; Inflammation; Athletes; Swimming; Asthma
PubMed: 34839784
DOI: 10.1080/17461391.2021.2008014 -
Trends in Cognitive Sciences Feb 2021The human sense of smell can accomplish astonishing feats, yet there remains a prevailing belief that olfactory language is deficient. Numerous studies with English... (Review)
Review
The human sense of smell can accomplish astonishing feats, yet there remains a prevailing belief that olfactory language is deficient. Numerous studies with English speakers support this view: there are few terms for odors, odor talk is infrequent, and naming odors is difficult. However, this is not true across the world. Many languages have sizeable smell lexicons - smell is even grammaticalized. In addition, for some cultures smell talk is more frequent and odor naming easier. This linguistic variation is as yet unexplained but could be the result of ecological, cultural, or genetic factors or a combination thereof. Different ways of talking about smells may shape aspects of olfactory cognition too. Critically, this variation sheds new light on this important sensory modality.
Topics: Biology; Humans; Language; Odorants; Olfactory Perception; Smell
PubMed: 33349546
DOI: 10.1016/j.tics.2020.11.005