Retronasal Olfaction Research Articles

A role for lung retention in the sense of retronasal smell.

In olfaction, odors typically engage the lungs on the way to the nose to evoke retronasal smell. This is most notable when the lung has a first pass effect during smoking/vaping, but also upon exhaling after sniffing an odor. The lungs act as a sink for odors, which can both reduce the retronasal odor concentration and the odor mixture makeup. Lung retention is a simple measure that quantifies the effectiveness of the sink. Lung retention has been studied in the context of environmental toxicology and is known for many volatile organic compounds. Available data on human lung retention suggests that the lungs may have a large impact on odor perception, and that this may depend heavily on the specifics of active sampling such as sniffing, smoking and vaping. Suggestions are included for transient measures and models of lung retention.

Direct behavioral and neurophysiological evidence for retronasal olfaction in mice.

The neuroscience of flavor perception is hence becoming increasingly important to understand food flavor perception that guides food selection, ingestion and appreciation. We recently provided evidence that rats can use the retronasal mode of olfaction, an essential element of human flavor perception. We showed that in rats, like humans, odors can acquire a taste. We and others also defined how the input of the olfactory bulb (OB) -not functionally imageable in humans- codes retronasal smell in anesthetized rat. The powerful awake transgenic mouse, however, would be a valuable additional model in the study of flavor neuroscience. We used a go/no-go behavioral task to test the mouse's ability to detect and discriminate the retronasal odor amyl acetate. In this paradigm a tasteless aqueous odor solution was licked by water-restricted head-fixed mice from a lick spout. Orthonasal contamination was avoided. The retronasal odor was successfully discriminated by mice against pure distilled water in a concentration-dependent manner. Bulbectomy removed the mice's ability to discriminate the retronasal odor but not tastants. The OB showed robust optical calcium responses to retronasal odorants in these awake mice. These results suggest that mice, like rats, are capable of smelling retronasally. This direct neuro-behavioral evidence establishes the mouse as a useful additional animal model for flavor research.

How the unique configuration of the human head may enhance flavor perception capabilities: an evolutionary perspective

How the unique configuration of the human head may enhance flavor perception capabilities: an evolutionary perspective

Scents and sensibility: how biology perceives chemistry

Everything we know about the world around us comes through our various sensory systems. Aristotle named five of these in human beings and for the last 2500 years that number has stuck. Even though it's not true. The classic five senses of Aristotle are vision, smell, taste, touch and hearing. We can add many others to these, either as subsets, or even as completely different senses. For example there is proprioception, the sense of your body's position in space, there is the vestibular system which tells you where your head is and in which way you pointed; touch should also include the thermal sensors for temperature and our multiple pain systems for acute, chronic, throbbing, aching, etc. types of pain. And the chemical senses, taste and smell, are in reality a group of multiple sensory systems capable of detecting and discriminating a wide variety of chemical structures and qualities.

Perceived minerality in Sauvignon wines: Influence of culture and perception mode

Description of wine in terms of perceived mineral character has become common practice in recent decades. The major aim of our study was to investigate cultural differences in perception of minerality in wines from France and New Zealand, these countries having very different wine-production histories. A second aim was to investigate influence of perception mode on perceived mineral character in wine to gain increased understanding of the metaphorical descriptor “mineral” as applied to wine chemosensory attributes. Thirty-two French and 31 New Zealand wine professionals evaluated 16 wines (8 French; 8 New Zealand) under three conditions: orthonasal olfaction; global (orthonasal and retronasal olfaction; taste; other palate sensations); and nose-clip (taste and palate sensations only). Results demonstrated that both French and New Zealand participants reported minerality to be perceived via all three perception modes. In terms of culture, similarities and differences were both observed in terms of quantitative judgments of minerality, and in terms of the wine attributes perceived as related to minerality. Cross-cultural differences were particularly evident in the global condition. Results are described in terms of cognitive processing of metaphorical terms employed to label perceived wine attributes.

Sensitivity and Specificity of Self-Reported Olfactory Function in a Home-Based Study of Independent-Living, Healthy Older Women.

The 2011-14 US National Health and Nutrition Examination Survey chemosensory protocol asks adults to self-rate their orthonasal (via nostrils) and retronasal (via mouth) smell abilities for subsequent odor identification testing. From data collected with a similar protocol, we aimed to identify a self-reported olfactory index that showed the best sensitivity (correctly identifying dysfunction) and specificity (correctly indentifying normosmia) with measured olfaction. In home-based testing, 121 independent-living older women (age 73±7 years) reported their olfactory function by interviewer-administered survey. Olfactory function was measured orthonasally via composite (odor threshold, identification task) or identification task alone. Only 16 % of women self-rated "below average" smell function. More women perceived loss of smell (38 %) or flavor (30 %) with aging. The rate of measured dysfunction was 30 % by composite (threshold and identification) and 21.5 % by identification task, the latter misclassifying some mild dysfunction as normosmia. An index of self-rated smell function and perceived loss yielded the most favorable sensitivity (65 %) and specificity (77 %) to measured function. Self-rated olfaction showed better agreement with severe measured dysfunction; mild dysfunction was less noticed. Self-reported indices that query about current and perceived changes in smell and flavor with aging showed better sensitivity estimates than those previously reported. Specificity was somewhat lower-some older adults may correctly perceive loss unidentified in a single assessment, or have a retronasal impairment that was undetected by an orthonasal measure. Our findings should inform self-rated measures that screen for severe olfactory dysfunction in clinical/community settings where testing is not routine.

Clinical assessment of olfactory functions in children who underwent adenotonsillectomy during pre- and post-operative period

ObjectiveThe aim of this study was to investigate the changes of both ortho- and retronasal olfactory function in children who underwent adenotonsillectomy (AT) operation due to infectious and/or obstructive adenotonsillar disease. Material and methodsA total of 25 children with adenotonsillar disease are included in the study; the children were followed for 6 months in the conducted clinics and underwent AT operation. An age- and sex-matched control group was constituted with 25 healthy children free of adenotonsillar disease. Adenoid and tonsillar hypertrophy was graded according to the subjective size scales. Each subject’s orthonasal and retronasal olfactory functions were assessed using odor identification test and retronasal olfactory testing. These tests were performed once, at the beginning of the study, for the control group and performed twice, at the beginning of the study and the third month follow-up, for the disease group. Parents of children in the adenotonsillar disease group filled out a visual analog scale to evaluate the children’s appetite at the same time with olfactory testing. ResultsThe current investigation produced four major findings: (1) both ortho- and retronasal olfactory abilities of participants were improving following AT operation, (2) adenoid hypertrophy had a significant negative effect on both ortho- and retronasal olfaction, whereas tonsil hypertrophy had significant negative effect only on the retronasal olfactory score, (3) retronasal olfaction was found to be more affected by the adenoid size than the orthonasal, as shown with correlation analysis, and (4) the increase in appetite of children after AT operation had been specified by parents. ConclusionsChildren with adenotonsillar disease have increased olfaction abilities, namely ortho- and retronasal olfactory function following AT operation. In addition, retronasal olfactory function, an important component of flavor, seems to be more affected than orthonasal function. These results also explain the increased appetite of operated children.

Grade 4 tonsillar hypertrophy associated with decreased retronasal olfactory function: a pilot study

Tonsillar hypertrophy is common in children, but it can also be present in adults. Enlarged tonsils, a significant anatomical barrier, may affect the flow of odor molecules from the oral cavity to the nasal passages, which has not yet been studied. Thus, we aimed to investigate the mass effect of palatine tonsillar hypertrophy on retronasal olfaction. This study was carried out in 146 subjects, with a mean age of 22.1 ± 2.2 years, ranging 20-29 years. An oropharyngeal examination of the participants was completed, and tonsillar hypertrophy was graded according to the subjective tonsil size scale. The participants were divided into four groups according to their tonsil size grading; then, each subject's orthonasal olfactory and retronasal olfactory functions were assessed using "Sniffin' Sticks" and retronasal olfactory testing. There were no differences observed between the groups in terms of age, gender, cigarette smoking, or alcohol consumption. In addition, there was no difference between the groups in terms of "Sniffin' Sticks" subtests and TDI scores. It was determined that the retronasal olfactory scores of the participants with grade 4 tonsil size were significantly lower than the retronasal olfactory scores of the participants with grade 1 tonsil size. The current investigation demonstrates that grade 4 tonsillar hypertrophy has significant negative effects on the retronasal route of olfactory sensing, when compared with grade 1 tonsillar hypertrophy.

Cigarette smoking and obesity are associated with decreased fat perception in women

ObjectiveSmoking and obesity are independently associated with high consumption of high-fat foods in women. We tested whether the co-occurrence of smoking and obesity associates with reduced oral fat perception.Design and MethodsFour groups of women (14 obese smokers, 11 obese never-smokers, 10 normal-weight smokers, 12 normal-weight never-smokers) rated vanilla puddings that varied in fat content for perceived intensity of creaminess and sweetness, using the general Labeled Magnitude Scale (gLMS), and degree of pleasantness, using the hedonic gLMS. To determine the role of retronasal smell, subjects rated puddings with and without noseclips.ResultsFor all groups, creaminess grew with increasing fat concentrations; puddings with any amount of fat were perceived as sweeter than fat-free pudding, and sweetness was enhanced when tasted without noseclips. Overall, obese smokers perceived less creaminess, sweetness, and pleasure while tasting the puddings than did the other three groups (all P-values<0.02).ConclusionThe ability to perceive fat and sweetness in and derive pleasure from foods is particularly compromised in obese women who smoke, which could contribute to excess calorie intake in this population already at high risk for cardiovascular and metabolic disease. Retronasal olfaction appears not to contribute to blunted flavor perception observed in obese smokers.

The Effect of Anatomic Clearance Between Tongue and Soft Palate on Retronasal Olfactory Function

Research shows that odorants travel to the olfactory receptors by two routes. Oral conditions, mouth movements, mastication, and swallowing are known to influence the perception of retronasal stimuli. The dimension of the anatomical clearance between the soft palate and tongue might affect the retronasal olfaction because retronasal olfaction is only possible when the soft palate–tongue barrier is opened. Therefore, in this present study, our aim is to evaluate the effect of the anatomical clearance between tongue and soft palate on retronasal olfactory function. After rating the mallampati score for the classification of the clearance between tongue and soft palate, the “Sniffin’ Sticks” test for orthonasal olfaction and retronasal olfactory testing were performed. The study was carried out on 276 subjects, and the mean age of the participants was 27 years ranging from 19 to 53 years. The participants were divided into two groups: Group 1 included participants with mallampati Class 1 and 2 scores; Group 2 included participants with mallampati Class 3 and 4 scores. This study clearly shows that the dimensional differences in the anatomical clearance between the soft palate and tongue had no effects on retronasal olfaction.

Making sense of the chemical senses.

We review our recent behavioural and imaging studies testing the consequences of congenital blindness on the chemical senses in comparison with the condition of anosmia. We found that congenitally blind (CB) subjects have increased sensitivity for orthonasal odorants and recruit their visually deprived occipital cortex to process orthonasal olfactory stimuli. In sharp contrast, CB perform less well than sighted controls in taste and retronasal olfaction, i.e. when processing chemicals inside the mouth. Interestingly, CB do not recruit their occipital cortex to process taste stimuli. In contrast to these findings in blindness, congenital anosmia is associated with lower taste and trigeminal sensitivity, accompanied by weaker activations within the 'flavour network' upon exposure to such stimuli. We conclude that functional adaptations to congenital anosmia or blindness are quite distinct, such that CB can train their exteroceptive chemical senses and recruit normally visual cortical areas to process chemical information from the surrounding environment.

An investigation of retronasal testing of olfactory function in a Turkish population

BackgroundThe aim of this study was: (1) to perform a preliminary study for the validation of “retronasal olfactory testing” in the Turkish population to find the best way to evaluate smell and taste disorders in Turkey; (2) to determine if cultural differences make application of the test more difficult; and (3) to determine the flavors that participants had not yet tasted by using the survey method.Material/MethodsThe study included 330 volunteers. Orthonasal olfactory function was assessed psycho-physically using the “Sniffin’ Sticks” olfactory test. Retronasal olfaction was assessed using a collection of 20 available food powders applied to the oral cavity. Also, all participants filled in a questionnaire of 50 items about the flavors they had not tasted before.ResultsThe mean age of the participants was 26±7.3 years. Participants were divided into 3 groups according to the “Sniffin’ Sticks” test results: anosmia, hyposmia, and normosmia groups. Differences in retronasal olfaction scores were significant among the 3 groups.ConclusionsThe retronasal olfactory test appeared to perform well, but modifications of odorized powders or granules and distracters used in the retronasal olfactory test, taking into account Turkish cultural differences, is likely to improve its performance.

Aroma volatile release kinetics of tomato genotypes measured by PTR-MS following artificial chewing

The aim of this study was to develop an analytical system to study the tomato aroma profile. An artificial chewing device coupled to a PTR-MS was developed to mimic, as close as possible, the release of volatiles during chewing in the human mouth and the retronasal olfaction perception.VOC profiles of 9 tomato lines, selected based on flavor characteristics by a sensory panel, were acquired by both a PTR-MS system following artificial chewing and by SPME–GC–MS and compared to the quantitative descriptive analysis (QDA) measured by the trained sensory panel.Based on multivariate statistical analysis, data obtained by the PTR-MS system showed a better correlation to the outcome of the QDA than SPME–GC–MS, especially for the descriptive parameters “tomato fragrance” and “tomato flavor”.The great advantage of such an analytical system was the possibility to study the release kinetics of volatiles during eating and the possibility to consider volatile concentration similar to in vivo condition resulting to an improved characterization of the aroma profile.

Color–Odor Interactions: A Review and Model

Certain colors are seen as corresponding to, and thus appropriate to, certain odors (e.g., red for cherry odor). When colors accompany odors, our perceptions of the odors are changed. Appropriate colors often affect our perception of the odors differently from inappropriate colors. This paper discusses the literature on color–odor correspondences including possible causes of these correspondences. It then reviews findings on the influence of color on odor identification, odor discrimination, odor intensity, and odor pleasantness. Color's effect on both orthonasal and retronasal olfaction is discussed. A model for how color exerts its effects on odor is proposed.

Glomerular input patterns in the mouse olfactory bulb evoked by retronasal odor stimuli

BackgroundOdorant stimuli can access the olfactory epithelium either orthonasally, by inhalation through the external nares, or retronasally by reverse airflow from the oral cavity. There is evidence that odors perceived through these two routes can differ in quality and intensity. We were curious whether such differences might potentially have a neural basis in the peripheral mechanisms of odor coding. To explore this possibility, we compared olfactory receptor input to glomeruli in the dorsal olfactory bulb evoked by orthonasal and retronasal stimulation. Maps of glomerular response were acquired by optical imaging of transgenic mice expressing synaptopHluorin (spH), a fluorescent reporter of presynaptic activity, in olfactory nerve terminals.ResultsWe found that retronasally delivered odorants were able to activate inputs to multiple glomeruli in the dorsal olfactory bulb. The retronasal responses were smaller than orthonasal responses to odorants delivered at comparable concentrations and flow rates, and they displayed higher thresholds and right-shifted dose–response curves. Glomerular maps of orthonasal and retronasal responses were usually well overlapped, with fewer total numbers of glomeruli in retronasal maps. However, maps at threshold could be quite distinct with little overlap. Retronasal responses were also more narrowly tuned to homologous series of aliphatic odorants of varying carbon chain length, with longer chain, more hydrophobic compounds evoking little or no response at comparable vapor levels.ConclusionsSeveral features of retronasal olfaction are possibly referable to the observed properties of glomerular odorant responses. The finding that retronasal responses are weaker and sparser than orthonasal responses is consistent with psychophysical studies showing lower sensitivity for retronasal olfaction in threshold and suprathreshold tests. The similarity and overlap of orthonasal and retronasal odor maps at suprathreshold concentrations agrees with generally similar perceived qualities for the same odorant stimuli administered by the two routes. However, divergence of maps near threshold is a potential factor in perceptual differences between orthonasal and retronasal olfaction. Narrower tuning of retronasal responses suggests that they may be less influenced by chromatographic adsorption effects.

High-Resolution Time–Intensity Tracking of Sustained Human Orthonasal and Retronasal Smelling During Natural Breathing

Perceived intensities of continuously available orthonasal and retronasal vapor-phase stimuli during natural breathing for approximately the first minute of smelling were not known in detail. To clarify this, stimuli presented continuously in vapor phase orthonasally or retronasally during natural breathing were time–intensity tracked over 55 s by 19 participants, with tracked intensities measured every 100 ms. Before the tracking session, participants individually matched concentrations of anise, coffee, peppermint, and strawberry flavors to the intensity of a fifth stimulus, orange. These were their tracked concentrations. During the intensity tracking sessions, real-time visual feedback of judged intensity was provided on a computer display. Participants controlled the vertical position of the display (intensity) while the horizontal position (time) advanced at a constant rate under program control, creating an image of intensity with respect to time. It was found that during natural breathing, retronasal-tracked intensity increased to maximum at ∼8 s, but was approximately half of orthonasal tracked maximum intensity, reached after ∼11 s. Within the 55-s tracking period, retronasal and orthonasal maxima exceeded their initial and final intensities. Final intensities at 55 s were approximately half of the maximum intensities. These data indicate, with high-resolution tracking during natural breathing of continuously presented vapor-phase stimuli, that intensity of smelling increases to a maximum after initial intensity is perceived, and that smelled intensity then declines slowly during approximately the first minute of smelling.

Comparison in taste and extractive components of boiled dorsal muscle and broth from half-smooth golden puffer Lagocephalus spadiceus caught in Japan with those of the same fish imported

The taste and extractive components of boiled dorsal muscle and broth prepared from half-smooth golden puffer Lagocephalus spadiceus caught in Japan and from those imported from China were compared. In the sensory test, the first taste, elasticity, and saltiness of boiled muscle from Japanese (domestic) fish were higher than those of the imported fish, whereas the orthonasal fishy smell of the imported fish was higher than that of the domestic fish. The first taste, aftertaste, retronasal fishy smell, sweetness, saltiness, and umami of the broth prepared from dorsal muscle of the domestic fish were higher than those of the imported fish, whereas orthonasal fishy smell and bitterness of the imported fish were higher than those of the domestic fish. Most panelists preferred the overall taste of the domestic fish to that of the imported fish. The concentration of trimethylamine in the trichloroacetic acid extracts from boiled muscle and broth of the imported fish was higher than that of the domestic fish, suggesting that this substance contributes to the orthonasal fishy smell of the imported fish.

Retronasal Olfaction in Vegetable Liking and Disliking

While previous research has suggested that bitterness is a key determinant of vegetable rejection, it is unknown what role odor may play. We therefore investigated the impact of retronasal odors on hedonic responses to 4 vegetables. Subjects (N = 132) tasted small samples with the nose open and closed and rated the degree of liking/disliking, as well as the perceived intensity of sweetness, bitterness, saltiness, and vegetable flavor. The subjects were classified as "likers" or "dislikers" of each vegetable. The degree to which "likers" liked and "dislikers" disliked the vegetables was significantly less in the nose-closed condition, indicating that retronasal odor was a significant driver of vegetable hedonics. In contrast, bitterness ratings for all 4 vegetables did not differ significantly between the groups. The perceived intensity of vegetable flavor also did not differ significantly between groups, implying that the quality of vegetable odors rather than their perceived intensity drove the hedonic ratings. In a follow-up experiment, returning subjects (N = 89) rated the degree of liking/disliking of the vegetable odors alone, which were presented retronasally. Liking/disliking of specific odors was positively correlated with that for the sampled vegetables across all stimuli (r = 0.32~0.57). Overall, these results suggest that retronasal odor plays an important role in vegetable liking/disliking.

Taste damage (otitis media, tonsillectomy and head and neck cancer), oral sensations and BMI

Otitis media and tonsillectomy are associated with enhanced palatability of energy dense foods and with weight gain. Otitis media can damage the chorda tympani nerve (CN VII); tonsillectomy and head and neck radiation treatment can damage the glossopharyngeal nerve (CN IX). Both of these nerves function prominently in taste sensation. The present study utilizes these sources of damage to study central interactions among the nerves that mediate oral sensations. Mild damage restricted to one of these nerves can actually intensify sensations evoked from undamaged nerves (i.e., whole‐mouth taste, oral tactile sensations evoked by fats and irritants). These intensifications may result from disruption of central inhibitory taste circuits, as taste damage appears to disinhibit other oral sensory nerves. In addition, mild damage restricted to one taste nerve can intensify odors perceived from foods in the mouth during chewing and swallowing (i.e., retronasal olfaction); this may be a secondary consequence of the intensification of whole-mouth taste. Damage to both nerves leads to widespread oral sensory loss. At present, the link between sensory alterations and weight gain has not been established for adults (e.g., does increased fat preference occur in individuals with oral sensory intensifications, those with losses, or both?). Finally, pain in non-oral locations is also related to taste loss. When participants rated “the most intense pain of any kind they had ever experienced,” those with the greatest taste loss gave the highest ratings. These effects suggest that taste loss significantly influences long-term health outcomes.

Retronasal Odor Representations in the Dorsal Olfactory Bulb of Rats

Animals perceive their olfactory environment not only from odors originating in the external world (orthonasal route) but also from odors released in the oral cavity while eating food (retronasal route). Retronasal olfaction is crucial for the perception of food flavor in humans. However, little is known about the retronasal stimulus coding in the brain. The most basic questions are if and how route affects the odor representations at the level of the olfactory bulb (OB), where odor quality codes originate. We used optical calcium imaging of presynaptic dorsal OB responses to odorants in anesthetized rats to ask whether the rat OB could be activated retronasally, and how these responses compare to orthonasal responses under similar conditions. We further investigated the effects of specific odorant properties on orthonasal versus retronasal response patterns. We found that at a physiologically relevant flow rate, retronasal odorants can effectively reach the olfactory receptor neurons, eliciting glomerular response patterns that grossly overlap with those of orthonasal responses, but differ from the orthonasal patterns in the response amplitude and temporal dynamics. Interestingly, such differences correlated well with specific odorant properties. Less volatile odorants yielded relatively smaller responses retronasally, but volatility did not affect relative temporal profiles. More polar odorants responded with relatively longer onset latency and time to peak retronasally, but polarity did not affect relative response magnitudes. These data provide insight into the early stages of retronasal stimulus coding and establish relationships between orthonasal and retronasal odor representations in the rat OB.