IntroductionPrevious 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.MethodsTwo 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.ResultsIn 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.ConclusionsExposure to putrescine may activate psychological threat management processes, which are then interpreted as higher life satisfaction.ImplicationsHuman olfactory perception is sensitive to putrescine, and putrescine may exert some subtle psychological effects on human cognition.

IntroductionOlfactory habituation results from prolonged exposure to an odor, leading to perceptual changes defined by several characteristics. To date, human habituation research has focused on orthonasal olfaction which is perceived externally while ignoring internal routes of odor perception related to flavor. In our study, we conducted two experiments to characterize retronasal olfactory habituation and measured its impact on flavor perception.MethodsIn Experiment 1, participants were presented a food odor and non-food odor retronasally, using an orally adhered strip. Each participant rated the odor intensity using a time-intensity procedure. After exposure, the participants ate a lime-flavored gummy and rated the lime flavor. In experiment 2, the same procedure was performed for a low-level lime odor, a simple (lime oil) and complex (lime oil + sucrose + citric acid) beverage as the flavor stimuli.ResultsOur results demonstrated two known principles of habituation for retronasally presented odors: (1) prolonged exposure leads to decreased perception and (2) weaker stimuli lead to more rapid habituation. Additionally, we found that the non-food odor habituated slower than the food odor; however, the participants seemed to recover simultaneously upon food and beverage consumption leading to no change in flavor perception.ConclusionThe findings of this study give evidence that we habituate to different odors at different rates; more specifically, we provide evidence that differentiates between odor origin and concentration.ImplicationsThis is the first time-intensity characterization of retronasal odor habituation. Additionally, a novel method of administering retronasal odors is presented.

IntroductionIn daily life, people encounter a wide range of odors, most of which contain multiple chemical substances. So-called bimodal odors stimulate both the olfactory and trigeminal nerve, and the interaction between these two systems shapes the perception of the odor. However, temporal encoding of these sensory systems during bimodal odor processing has received limited scientific attention.MethodsTo investigate this, we recorded the electrophysiological response in 17 participants to relatively unimodal olfactory (strawberry), trigeminal (l-isopulegol) and strongly bimodal (strawberry and l-isopulegol) stimuli.ResultsERP amplitudes and intensity ratings were significantly bigger for bimodal stimulation, as compared to unimodal stimulations. No significant difference was observed between N1 and P2 response latencies to olfactory and bimodal stimuli while responses to both stimuli showed longer latencies compared to the response of the trigeminal stimulus.ConclusionsResults provide further evidence of interaction between olfactory and trigeminal systems; additional activation of the olfactory system results in more vigorous electrophysiological responses and the experience of higher intensity. In addition, results indicate that the trigeminal system is faster to react to stimulation.ImplicationsThe current study offers a view on the temporal processing of bimodal odorants that are most likely to be encountered in the environment. We link the more vigorous electrophysiological response to a more complex odorant with activation of different neural structures.

IntroductionOdor perception is biased by verbal–semantic processes when cues on an odor’s source are readily available from the context. At the same time, olfaction has been characterized as basically sensation driven when this information is absent. In the present study, we examined whether language effects occur when verbal cues are absent and how expectations about an odor’s identity shape odor evaluations.MethodsA total of 56 subjects were asked to rate 20 unlabeled odor samples on perceptual dimensions as well as quality attributes and to eventually provide an odor source name. In a subsequent session, they performed the same rating tasks on a set of written odor labels that was compiled individually for each participant. It included both the 20 correct odor names (true labels) and in any case of incorrect odor naming in the first session, the self–generated labels (identified labels).ResultsWe compared odor ratings to ratings of both types of labels to test whether differences between odor and odor label evaluations were rooted in identification mechanisms. In cases of false identifications, we found higher consistencies between the evaluation of an odor and its identified label than between the description of an odor and its true (yet not associated) label.ConclusionsThese results indicate that odor evaluations are strongly affected by the mental image of an odor rather than the actual sensory codes and that this mental image is built spontaneously. Our findings imply that odors and odor labels are evaluated similarly for identical objects and that the differences found in similar studies may have been rooted in different mental representations being evaluated.ImplicationsOdor sensations provoke odor naming without explicit demand. These self–generated hypotheses about an odor’s source exert a considerable semantic impact on odor perceptual processing, regardless of their accuracy.

IntroductionWithholding uninitiated actions and cancelling ongoing ones are two main components of response inhibition, a key element of the executive control. Inhibitory performance is sensitive to emotional contexts elicited by subliminal and supraliminal visual material. However, whether stimuli from other sensory modalities, such as odours, would equally modulate response inhibition remains unclear. Here, we aimed to assess the effect of task-irrelevant odours as a function of their valence and threshold on both action withholding and action cancellation of reach-to-press movements.MethodThirty-two healthy participants performed a Go/No-Go task that included the presentation of pleasant (orange) and unpleasant (trimethyloxazole) odour primes at supra- and sub-threshold levels; clean air was included as a control condition. The reach-to-press responses were composed of an initial release phase and a subsequent reaching phase.ResultsOnly the supra-threshold pleasant (vs. control) odour impaired action withholding. Moreover, the pleasant (vs. control) odour—presented at both sub- and supra-threshold levels—elicited more accurate Go responses, whereas the sub- and supra-threshold pleasant and unpleasant (vs. control) odours triggered faster responses in the release phase. Additionally, only the supra-threshold pleasant (vs. unpleasant) odour impaired action cancellation in the reaching phase. Furthermore, reaching responses were slower following the supra-threshold unpleasant (vs. control) odour.ConclusionsOur findings extend the sparse literature on the impact of odour stimuli on goal-directed behaviour, highlighting the role of both odour valence and threshold in the modulation of response inhibition.ImplicationsDetermining the mechanisms by which odour stimuli modulate response inhibition lays the foundations for research on odour-triggered disinhibition.

IntroductionSenses such as thirst, hunger, pain, and temperature sensation show imbalances of the internal state and have important implications for survival. Independently, thirst and pain perception create motivational states that organize behavior to fulfill the goal imposed by the perception, but little is known on how competitive these perceptions are when combined and the motivational states they create when experienced in unison.MethodsA review of the literature was conducted about pain, thirst, and vasopressin. Specific inclusion was given to studies observing the association of pain and thirst together and independently.ResultsArticles that were reviewed were original research, reviews, and large clinical studies. Results from previous research show a relationship between motivational states, such as thirst and pain perception.ConclusionsThirst and pain are competitive motivational states that arise certain behaviors for a specific goal. Further research is needed to understand how these motivational states might be changed by one another.ImplicationsFrom this review, readers can conclude that increased thirst can bring about greater pain sensation for given stimuli.

IntroductionIf odor and taste are presented in a context with high temporal proximity, they are more likely to be perceived as a flavor object. However, if odor and taste are presented in a context with low temporal proximity as well as a context with high temporal proximity, they may be less likely to be perceived as a flavor object. Based on these expectations, we hypothesized that sensitivity to temporal difference between two sensations (i.e., temporal resolution of synchrony perception) is higher when odor and taste are presented under a condition including a context with low temporal proximity than under a condition excluding it.MethodsTo test this hypothesis, we required participants to determine whether olfactory and gustatory stimuli were presented simultaneously under a condition including a context with low temporal proximity (wide-range condition) and under a condition excluding it. In addition, we also tested visual–gustatory and olfactory–visual combinations.ResultsThe temporal resolution was significantly higher under the wide-range condition than under the narrow-range condition, supporting our hypothesis.ConclusionFor odor and taste to be perceived as flavor, people not only must experience high temporal proximity of the two sensations but also must not experience low temporal proximity of the two sensations.ImplicationThe findings of this study suggest that the higher the sensitivity to a temporal difference between odor and taste, the lower the robustness of a flavor object (i.e., the strength of the odor–taste connection).

BackgroundA card-type odor identification test called the “Open Essence (OE),” consisting of 12 types of everyday odors familiar to Japanese people, was recently developed. In this study, we calculated the cut-off value of the OE score for screening for age-related olfactory decline.MethodsParticipants aged 23 to 91 performed the OE test. After we confirmed that the OE score differed significantly between young/middle-aged adults (under 65 years old) and elderly adults (over 65 years old), we assumed that the young/middle-aged group had normal olfactory ability, whereas the elderly group had experienced a decline in odor identification ability. We then performed receiver operating characteristic (ROC) analysis using the OE score.ResultsThe cut-off value of the OE score for screening for age-related olfactory decline, calculated on the basis of the ROC curve, was 8.ConclusionIndividuals with the OE scores of 7 or less may have age-related olfactory decline. Our finding suggests that this cut-off value could be used to screen Japanese people with age-related olfactory decline.ImplicationThe OE test is self-administered and has a cut-off value of the OE score for screening for age-related olfactory decline. Therefore, it is expected to be useful in mass screening for elderly adults.

IntroductionBrain activation in response to olfactory stimuli has been studied using functional magnetic resonance imaging (fMRI), but there is little knowledge about processing repeated olfactory information which is usual in daily life.MethodsThis fMRI study was designed to investigate brain response to repeated odorant stimulation with positive and negative valences in 12 healthy right-handed volunteers. There was a 25-min rest interval between two fMRI runs with identical stimulation paradigms with two odors, as phenylethyl alcohol (PEA) and isovaleric acid (IVA), and the two odors were released alternately.ResultsThere was a similar activation pattern in regions of primary and secondary olfactory cortex induced by odors of both valences, especially by negative odor. Weakened activation of the brain is responsive to repeated both pleasant and unpleasant smell. Nevertheless, the repeated unpleasant odor has a more intimate relationship with the piriform cortex, amygdala, and hippocampus.ConclusionWe conclude that asymmetric brain activation in response to repeated odorant stimulation depended on valences and that the unpleasant odor can evoke more negative emotion and profound memory.ImplicationsWe explore the central processing about repeated olfactory information applied fMRI for the first time, revealing asymmetric brain activation in response to repeated odors of pleasantness and unpleasantness.

IntroductionHyposmia and metacognitive errors are related to aging, depression, male gender, and cognitive decline. The current study investigated the awareness of olfactory dysfunction in subjective cognitive decline (SCD), mild cognitive impairment (MCI), and Alzheimer’s disease (AD), as well as the influence of additional factors.MethodsA sample of 641 patients, including controls, SCD, non-amnestic MCI (naMCI), amnestic MCI (aMCI), and AD patients, was assessed with the Sniffin’ Sticks odor identification test (OIT) and the subjective olfactory capability (SOC) scale, in addition to measures of depressive symptoms, verbal memory, and executive functioning. Olfactory awareness groups were formed by means of the cutoffs of the OIT and the SOC.ResultsModerate and small, although significant, correlations between the OIT and the SOC were found among the study groups, with a significant discrimination of measured olfactory function via subjective assessment existing among controls but not among patients with AD. Of all AD patients, 34% overrated their sense of smell while 21% correctly identified themselves as being hyposmic, as opposed to corresponding 6% and 1% of healthy elderly. Overraters and correct hyposmic participants showed higher age and worse verbal memory and executive functions.ConclusionsReduced odor identification might underlie the same pathological changes within the brain as cognitive impairment and could serve as an additional marker for the development of AD.ImplicationsAlthough people with AD are aware of hyposmia to some extent, the majority is affected by overestimation of the ability to smell, making the combination of subjective ratings and measures of olfactory function an interesting topic for further research.

IntroductionChanges in olfactory perception observed in cross-sectional studies may not reflect actual ongoing change within individuals. The aim of the present study was to assess intra-individual as well as inter-individual variation in olfactory scores in pre-schoolers across five waves over a 2-year period.MethodsThe participants were 157 children (79 boys) aged 5.8 ± 0.6 years at initial testing. We repeatedly examined the effects of time, age, gender, test practice, operationalised as the number of sessions attended and the intervals between them, and influence of school entry on identification, discrimination, and threshold Sniffin’ Sticks scores. Data imputation was performed due to missing data.ResultsIn non-imputed data, odour identification and discrimination were higher in girls. More odours were also correctly identified by children who had attended fewer sessions in shorter intervals. In imputed data, in addition to these effects, odour identification and discrimination increased further into the study and were higher in children who were older at initial testing and those who had started attending school. Schoolchildren also had lower thresholds than pre-schoolers. However, both the significant and non-significant effects were generally small.ConclusionsWe observed mainly small effects of gender and test practice on odour identification and discrimination, whereas intra-individual variation appeared only after data imputation.ImplicationsIt is likely that olfactory development over time needs to be observed for longer than 2 years.

IntroductionCOVID-19 infection develops neurologic symptoms such as smell and taste loss. We aimed to determine the volumetric changes in the brain and correlation of possible related biochemical parameters and endocannabinoid levels after COVID-19 recovery.MethodsBrain magnetic resonance images of recovered COVID-19 patients and healthy volunteers, whose olfactory and gustatory scores were obtained through a questionnaire, were taken, and the volumes of the brain regions associated with taste and smell were measured by automatic and semiautomatic methods. Endocannabinoids (EC), which are critical in the olfactory system, and vitamin B12, zinc, iron, ferritin, thyroid-stimulating hormone (TSH), and thyroxine (T4) levels, which are reported to have possible roles in olfactory disorders, were measured in peripheral blood.ResultsTaste and smell disorder scores and EC levels were found to be higher in recovered COVID-19 patients compared to controls. EC levels were negatively correlated with bilateral entorhinal cortex (ENT) volumes in the COVID-19 group. Subgenual anterior cingulate cortex volumes showed correlations with gustatory complaints and ferritin in recovered COVID-19 patients.ConclusionsThe critical finding of our study is the high EC levels and negative correlation between EC levels and left ENT volumes in recovered COVID-19 patients.ImplicationsIt is possible that ECs are potential neuromodulators in many conditions leading to olfactory disorders, including COVID-19.

IntroductionA high level of disgust propensity (the general tendency to respond with the emotion of disgust to any given situation) is associated with an increased sensitivity to bitter taste. The present study examined the relationship between disgust propensity and the sensitivity to bitter aftertaste.MethodsA total of 200 women rinsed their mouth with concentrated wormwood tea (Artemisia absinthium). The resulting aftertaste was evaluated (intensity of bitterness and disgust) every 15 s for 10 min. A multiple linear regression analysis was calculated to capture the association between aftertaste ratings and affective variables (e.g., disgust propensity, depression symptoms).ResultsHigher disgust propensity was associated with higher initial disgust ratings and faster reduction of disgust over time. Higher depression scores were associated with a slower disgust reduction.ConclusionWe demonstrated that affective variables predict the temporal course of the wormwood aftertaste response. Having a higher disgust propensity was associated with a shortened disgust recovery.ImplicationsA shortened disgust recovery may be adaptive because it enables faster processing of new disgust stimuli.

IntroductionPrevious studies have described a number of protein tyrosine kinases (epidermal growth factor receptor, ErbB2, ErbB3, and c-kit) to be expressed in taste bud cells, their innervating nerves, and in developing taste papillae.MethodsImmunohistochemical staining of mouse taste buds was performed to characterize the expression patterns of the c-kit receptor in taste.ResultsHere we demonstrate that c-kit positive cells are exclusively co-localized with T1R3 (which forms one half of the receptors for sweet and umami taste) in adult taste cells.ConclusionsThis implies that c-kit+ cells are primarily taste cells that respond to sweet and umami, but not to bitter, sour, or salty. These data indicate that the control of c-kit activation may be important for proper taste bud formation and may aid in the maintenance of this specific mature taste cell subpopulation.ImplicationsFurther characterization of the functional role of c-kit in taste may lead to superior taste cell cultures or organoids, and elucidate mechanisms of taste cell regulation.

IntroductionWomen’s olfactory perception varies across the menstrual cycle. The influence of oral contraceptives on this variability remains unclear.MethodsTo further estimate this, we assessed discrimination performance for both body odors and ordinary odorants in 36 women, 18 naturally ovulating, and 18 using oral contraceptives. Each participant was tested once a week over the course of a month, and data was then parsed into menstrual phases.ResultsIn naturally ovulating women, at the transition from follicular to luteal phases, there was a decline of 19% (p = 0.003) in olfactory discrimination of body odors but not ordinary odorants. In turn, in women using oral contraceptives, only at a later time of the month, at a point corresponding to the late luteal phase and shift from post-ovulation to pre-menstruation, was there a decline of 20% (p = 0.002) in olfactory discrimination performance. Moreover, when we reorganized the data from women using oral contraceptives in order to separately assess the contraceptive withdrawal period (the few days off pills), we observed a 23% reduction (p = 0.01) in discrimination accuracy of body odors but not ordinary odorants during this time alone.ConclusionsWomen have reduced ability to discriminate body odors during the withdrawal period of oral contraception.ImplicationsIf women indeed consider men’s body odor in their mate selections, then the oral contraception withdrawal period may not be the best time to make such decisions.

IntroductionDuring sensory evaluations of minty products, white chocolate is proposed as a palate cleanser between sample tastings. However, this is not an evidence-based practice, as no literature proves this. The aim of this study was therefore to identify the best palate cleanser to use in sensory evaluation of minty confectionery products.MethodsThree chewing gums with different cooling intensity were chewed for 3 min by a trained panel and evaluated for overall cooling, nose tingling, mouth burning, minty aroma, and sweetness. After the sample tasting, the following different palate cleansers were proposed: low-salt breadstick, whole milk, milk chocolate, white chocolate, and sunflower oil, compared with the resting time (control). The residual sensations were measured for the next 15 min.ResultsBreadstick and seed oil are the most effective palate cleansers on overall cooling carry-over. White chocolate seems to be effective on mint aroma, but this is likely to be due to its strong flavour, masking other perceptions. Moreover, both white and milk chocolates affect negatively the sweetness perception, by increasing it soon after the consumption, and even impacting on the next sample evaluation.ConclusionsNone of the palate cleansers were able to fully re-establish the oral environment after 15 min. Therefore, further studies on combinations, or on repeated use of the same palate cleanser, are proposed.ImplicationsThe use of an effective palate cleanser can reduce the time for product testing and increase data precision. Finding a proper palate cleanser for minty products is a strategy to optimise sensory evaluations in confectionery industry.

IntroductionAlthough most US adults drink alcoholic beverages, little is known about the association between drinking and taste. We hypothesized that the ability to distinguish differing intensities of bitter and salt solutions would be poorer among drinkers than nondrinkers.MethodsWe used cross-sectional data from 4990 participants aged 40+ from a large, national survey of the US population (National Health and Nutrition Examination Survey, 2012–2014). The validated generalized Labeled Magnitude Scale (gLMS) was used to rate participants’ perception of the intensities of a series of bitter (1 mM quinine) and salt (0.32 M and 1 M NaCl) solutions. Statistical analyses, weighted to produce nationally representative estimates, were adjusted for factors including race/ethnicity, education, marital status, income, body mass index (BMI), smoking, physical activity, self-reported health status, diabetes, depression, and use of medications known to affect taste.ResultsIn adjusted analyses, ability to distinguish intensity of a salt solution (0.32 M) was poorer among older (aged 60+) female current drinkers than their nondrinking counterparts (p = 0.001). Ability was also poorer among drinkers who consumed wine in the past 24 h compared to drinkers who consumed no alcohol during that time (p = 0.016). Ability to distinguish different intensities of the bitter solution was poorer among more frequent wine consumers (p = 0.034).ConclusionsWe found few significant associations. However, the result for older women is potentially interesting given recent increases in drinking within that population.ImplicationsTaste is a novel consideration in research on alcohol consumption. We encourage further exploration in this area.

IntroductionThe characteristics and impact of mouthfeel, temperature, smell, and taste alterations in patients with COVID-19 at a long term are yet not well known. In this study, these characteristics and their impact on daily life and quality of life (QoL) were assessed, six to ten months after infection, in patients with COVID-19 searching for peer support on Facebook.MethodsBetween December 2020 and January 2021, members of two COVID-19 Facebook groups were invited to complete a questionnaire. Participants were asked to report their perception of mouthfeel, temperature, smell, and taste alterations and their impact.ResultsThe questionnaire was completed by 157/216 respondents (73%), with 92% being women. Alterations in mouthfeel, temperature, smell, and taste were reported by respectively 66, 40, 148, and 133 participants. The most frequently reported mouthfeel alterations were “a different feeling” and “dry mouth” in 38 and 30 participants, respectively. Preferences for food temperature were equally changed to “freezing”, “cool”, “room temperature”, “a bit warmer”, and “warmer”. An impact on daily life and QoL was reported by most patients with alterations in mouthfeel (91% and 79%), temperature (78% and 60%), smell (98% and 93%), and taste (93% and 88%), respectively.ConclusionsPatients with COVID-19 searching for peer support on Facebook experienced, next to smell and taste alterations, mouthfeel and temperature disturbances, six to ten months after infection. These alterations have an impact on daily life and QoL.ImplicationsHealth professionals should, next to smell and taste alterations, be aware of mouthfeel and temperature alterations in patients with COVID-19.

IntroductionOdor imagery is known to be more difficult than any other modality of sensory imagery. Consequently, wide between-individuals variability can be found in odor imagery ability. Several studies have shown a positive relationship between olfactory performance and odor imagery ability. In the light of factors known to influence smelling ability, this study therefore investigated the effects of two factors — gender and age — known to influence smelling ability, on self-declared odor imagery ability in normosmic individuals.MethodsSeven hundred and nine French participants were asked to complete the web version of the French Vividness of Olfactory Imagery Questionnaire (fVOIQ). General linear models were used to determine the contributions of gender and age to odor imagery vividness scores. Moreover, scores were compared between age intervals ranging from 18–30 years old to 60 + years old.ResultsOur findings reveal that at any age, men and women have the same odor imagery ability. Odor imagery ability in self-declared normosmic individuals improves with age until 50–60 years old, and beyond this point the often-reported age-related olfactory decay does not alter it.ConclusionsThese findings suggest a high contribution of daily olfactory experience to the development of this cognitive function, and a relationship with olfactory performance that appears less linear than hypothesized.ImplicationsThis study provides food for thought in the field of olfaction: it suggests that distinct mechanisms may underlie two cognitive processes, perception and sensory imagery.