Diet and odor hedonic ratings: comparative study between vegetarians, flexitarians, and omnivores.

OBJECTIVES: Odor hedonic perception is well known to exhibit great variability and to depend on several parameters, i.e. stimulus, context, and subject characteristics. As hedonic perception (pleasant/unpleasant character) of food odors is considered one of the most prominent dimensions in eating behavior, the question of hedonic variability in this context arises. Thus, the aim of the present study was to compare odor hedonic ratings in three populations with regard to diet (i.e. omnivore, vegetarian, and flexitarian diets). METHODS: Four categories of odors were compared: meat, vegetable, other food, and non-food odors. RESULTS: The results showed that vegetarian and flexitarian individuals rated meat odors as more unpleasant than omnivores, while no significant difference was found for other categories of odors. DISCUSSION: The question of whether the diet influences the hedonic perception or/and inversely is discussed, regarding several aspects of food consumption such as eating disorders, food education, … and could further serve to manage eating behaviors. PRACTICAL APPLICATIONS: This study evidenced that vegetarians and flexitarians specifically rated meat odors as being more unpleasant than those of omnivores. Because of the growing number of vegetarians and flexitarians in the general population, it could be suggested to take into account the odor hedonic perception (especially regarding food odors) in studies related to diets. Besides, the present results could further serve research in several aspects of food consumption such as eating disorders (anorexia, bulimia … etc.) or food education as well as the management of eating behaviors, especially in an elderly population.

[Aging and disorders of taste and smell]. / Vieillissement et troubles du goût et de l'olfaction.

Compared with other sensory modalities, age-related alterations in taste and smell are less known and less investigated in clinical practice. In fact, the elderly with a loss of smell or taste may not always report it or be aware of it. In addition, the clinical evaluation of taste and smell by specific tests is rarely performed.

Thoughts and sensations, twin galaxies of the inner space: The propensity to mind-wander relates to spontaneous sensations arising on the hands.

Sensations and thoughts have been described as potentially related to self-awareness. We therefore asked whether sensations that arise in the absence of external triggers, i.e., spontaneous sensations (SPS), which were shown to relate to interoception and perception of the self, vary as a function of the individual propensity to generate spontaneous thoughts, i.e., mind-wandering. The Mind Wandering Questionnaire (MWQ) was used as a specific tool to assess the frequency and propensity to mind-wander several weeks before completing an SPS task. Correlational analyses between the MWQ score and SPS showed that greater propensity to mind-wander coincided with widespread perception of SPS, while lesser propensity to mind-wander coincided with more spatially restricted perception of SPS. The results are interpreted in light of the role of spontaneous thoughts and sensations in self-awareness. The potential psychological processes and the way they might regulate the relation between mind-wandering and the perception of SPS are discussed.

Variability in odor hedonic perception: A challenge for neurosensory and behavioral research.

Odor hedonic perception (pleasant/unpleasant character) is considered to be the first and one of the most important dimensions in olfaction and is known to be highly variable and dependent on several factors related to the stimulus, individual characteristics, and context. Although numerous experimental studies have been published on this topic, there is no comprehensive general review on the variability in odor hedonic perception. Therefore, the aim of this article was to describe and detail all the factors involved in the variability in odor hedonic perception. Stimulus properties-related variability includes the concentration/intensity and the physicochemical properties. Individual-related variability includes sex, age, and physiological state characteristics, while context-related variability involves factors associated with the stimulation context, such as stimulation pathway, exposure frequency, verbal influences, cross-modal associations, hedonic contrast, and cultural background. Subsequently, a section is devoted to the brain processing of odor hedonicity, although its role in odor hedonic variability is largely unknown. Finally, the article discusses the relationship between the hedonic qualities of odors and the resulting behavioral responses in both animals and humans. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

A study on the relationship between odor hedonic ratings and individual odor detection threshold.

Odor hedonic perception (pleasant/unpleasant character) is considered as the first and one of the most prominent dimensions in olfaction and is known to depend on several parameters. Among them, the relation between the odorant concentration and the hedonic estimation has been widely studied. However, few studies have considered odor hedonic ratings (OHR) in relation to individual detection thresholds (IDT). Thus, the aim of this study was to determine olfactory detection thresholds and to describe hedonic rating variations from individual thresholds to higher concentrations. IDT were performed for two pleasant (apple and jasmine) and two unpleasant (durian and trimethylamine) odorant stimuli. The experimenter presented one by one in a randomized order, the different odorant concentrations above IDT. Participants rated odor hedonic valence of these stimuli on a visual analog scale. Results showed, except for trimethylamine, the same relationship between hedonic ratings and stimulus concentration, i.e., an increase of pleasantness (apple and jasmine)/unpleasantness (durian) ratings at low and middle concentrations followed by a plateau at high concentrations. Correlations between OHR and concentrations as well as between OHR and threshold steps were always significant. Moreover, comparisons between both conditions showed that the correlation coefficient was significantly higher for trimethylamine (and a trend for apple) when IDTs were considered, while no difference was found for jasmine and durian. Overall, results suggested that the relationship between OHR and IDT is odor specific. These findings contribute to explain the large variability of the hedonic tone (i.e., weakly vs. very pleasant, weakly vs. very unpleasant) at specific concentration in the general population and could serve future research in this field (e.g., olfactory preferences in nutrition studies, anhedonia in psychiatric disorders…).

Toxicity of carbon dioxide: a review.

The toxicity of carbon dioxide has been established for close to a century. A number of animal experiments have explored both acute and long-term toxicity with respect to the lungs, the cardiovascular system, and the bladder, showing inflammatory and possible carcinogenic effects. Carbon dioxide also induces multiple fetal malformations and probably reduces fertility in animals. The aim of the review is to recapitulate the physiological and metabolic mechanisms resulting from CO(2) inhalation. As smokers are exposed to a high level of carbon dioxide (13%) that is about 350 times the level in normal air, we propose the hypothesis that carbon dioxide plays a major role in the long term toxicity of tobacco smoke.

Sex Differences in Odor Hedonic Perception: An Overview.

Odor hedonic evaluation (pleasant/unpleasant) is considered as the first and one of the most prominent dimension in odor perception. While sex differences in human olfaction have been extensively explored, gender effect in hedonic perception appears to be less considered. However, a number of studies have included comparisons between men and women, using different types of measurements (psychophysical, psychophysiological,…). This overview presents experimental works with non-specific and body odors separately presented as well as experimental studies comparing healthy participants vs patients with psychiatric disorders. Contrary to sensitivity, identification or discrimination, the overall literature tends to prove that no so clear differences occur in odor hedonic judgment between men and women. On the whole, gender effect appears more marked for body than non-specific odors and is almost never reported in psychiatric diseases. These findings are discussed in relation to the processes classically implied in pleasantness rating and emotional processes.

To the self and beyond: Arousal and functional connectivity of the temporo-parietal junction contributes to spontaneous sensations perception.

The temporoparietal junction (TPJ), along with the anterior insula (AI) and the extrastriate body area (EBA), play a major part in embodiment and self-awareness. However, these connections also appear to be frequently engaged in arousal and attentional processing of external events. Considering that these networks may focus attention both toward and away from the self, we set to investigate how they contribute to the perception of spontaneous sensations (SPS), a common phenomenon related to self-awareness and mediated by both interoceptive and attentional processes. In Experiment 1, resting-state EEG was recorded, as well as arousal reported via a questionnaire, followed by a SPS task. Functional TPJ-AI and TPJ-EBA connectivity were computed using eLORETA. Spatial correlational analyses showed that less frequent SPS coincided with greater TPJ-AI and TPJ-EBA functional connectivity, especially in the theta and alpha frequency bands. High self-reported arousal predicted low intensity and low confidence in the location of SPS. Resting-state skin conductance level (SCL) was recorded in Experiment 2, followed by the SPS task. Less frequent SPS coincided with greater SCL. Findings are interpreted in terms of attention and self-related processes, and a discussion of the TPJ participation in self-awareness through SPS is presented.

Effects of CO2 inhalation exposure on mice vomeronasal epithelium.

Nasal epitheliums are the first sites of the respiratory tract in contact with the external environment and may therefore be susceptible to damage from exposure to many toxic volatile substances (i.e., volatile organic components, vapors, and gases). In the field of inhalation toxicology, a number of studies have considered the main olfactory epithelium, but few have dealt with the epithelium of the vomeronasal organ (VNO). However, in several species such as in rodents, the VNO (an organ of pheromone detection) plays an important role in social interactions, and alterations of this organ are known to induce adaptative behavioral disturbances. Among volatile toxicants, health effects of inhaled gases have been thoroughly investigated, especially during CO(2) inhalation because of its increasing atmospheric concentration. Therefore, this work was designed to examine the effects of 3% CO(2) inhalation on VNO in two different exposure conditions (5 h/day and 12 h/day) in mice. Behavioral sensitivity tests to urine of congener and histological measurements of VNO were conducted before, during (weeks 1-4), and after (weeks 5-8) CO(2) inhalation exposures. Results showed no significant modifications of behavioral responses to urine, but there were significant changes of both cell number and thickness of the VNO epithelium. Moreover, the findings indicated a selectively dose-dependent effect of CO(2), and further research could use other gases in the same manner for comparison.

Assessment of Olfactory Perception in Individuals with Motion Sickness.

BACKGROUND: Individuals who experience motion sickness (MS) frequently mention the presence of smells in the environment as a factor favoring the occurrence of MS symptoms. The aim of the present work was to compare olfactory function in MS sensitive (MS+) and insensitive (MS-) subjects. METHODS: Olfactory testing included determination of odor detection thresholds, subjective evaluation of the quality (intensity, hedonicity, and familiarity) of three different odorants (limonene, isovaleric acid, and petrol) as well as measures of skin conductance responses to these three odorants. RESULTS: Results showed no difference in olfactory sensitivity between MS+ and MS- subjects. However, findings of both subjective (odor quality self-rating) and objective (psychophysiological responses) measures did reveal that the affective response to petrol odor was significantly different in MS+ and in MS- subjects. Indeed, on a scale from 0 (unpleasant) to 10 (pleasant) MS+ subjects rated petrol odor as more unpleasant (mean = 2.52) than MS- subjects (mean = 4.15) and rise-time of skin conductance responses to petrol odor was significantly longer in MS+ (mean = 5.98 s) compared to MS- subjects (mean = 3.22 s). DISCUSSION: Our study delves further into the knowledge of the relationship between motion sickness and olfaction by demonstrating a modified olfactory perception in motion sickness sensitive subjects at both the psychophysical and psychophysiological levels.Jacquot L, Millot J-L, Paillard AC. Assessment of olfactory perception in individuals with motion sickness. Aerosp Med Hum Perform. 2018; 89(5):428-433.

Comparative behavioral effects between synthetic 2,4,5-trimethylthiazoline (TMT) and the odor of natural fox (Vulpes vulpes) feces in mice.

Synthetic 2,4,5-trimethylthiazoline (TMT)--a component of red fox (Vulpes vulpes) feces--is frequently used to induce unconditioned fear in rodents. Surprisingly, direct comparison between TMT and natural fox feces odor is almost nonexistent. In this study, Experiment 1 compared the avoidance in relation to TMT concentration, natural fox feces, and gender of fox and mice. Results show that the avoidance is (a) higher with either pure or 50% TMT as compared to natural fox feces, whereas the difference is slight with 10% TMT, and (b) significantly higher for the female mouse group compared to the male mouse group with TMT as well as natural fox feces. In addition, no clear difference in effect was observed between male and female fox feces. Experiment 2 compared behavioral parameters recorded as an index of fear and anxiety, general activity, and avoidance in elevated plus-maze and open-field chamber between 10% TMT and natural fox feces in relation to the estrus cycle of the mice. Results show no cycle period effect--except for the avoidance parameter "distance to odorant"--and no different effects between 10% TMT and natural fox feces except for freezing.

Trigeminal sensitization and desensitization in the nasal cavity: a study of cross interactions.

Chemical irritation in the human nasal cavity is poorly documented. In this field, an important issue concerns the differential responses produced by successive stimulation. Repeated identical chemical irritant stimuli can produce increases or decreases in responses (two phenomena known as self-sensitization or self-desensitization). In the same way, different molecules can interact and produce cross-sensitization or cross-desensitization. The aim of this study was to contribute to this question using two specific molecules, acetic acid (AA) and allyl isothiocyanate (AIC). As the self-sensitization and -desensitization for AIC is known, a first experiment in the present work investigated the response, acute effects and time course of sensitization or desensitization to acetic acid. A second experiment tested the responses of acetic acid after a previous stimulation with allyl isothiocyanate (mustard oil) and inversely with a short inter-stimulus interval (ISI of 45 s). A third experiment similar to the second used a long inter-stimulus interval (ISI of 3 min 30). Twelve healthy subjects participated in the study using psychophysical (intensity ratings) and psychophysiological (skin conductance response) measurements. Firstly, the results showed that repeated nasal stimulation with acetic acid produced a self-desensitization whatever the ISI. Secondly, the results showed a cross-desensitization of allyl isothiocyanate by previous acetic acid stimulation. In contrast, previous stimulation with allyl isothiocyanate had no effect on the following acetic acid response. These findings confirm that trigeminal sensitization and desensitization in the nasal cavity do not follow the same processes in relation to molecules used.

My heart is in my hands: the interoceptive nature of the spontaneous sensations felt on the hands.

Somatic sensations may arise in the total absence of external stimuli, i.e., spontaneous sensations (SPSs). Because the background of body sensations has been mentioned as a possible contributor to interoceptive functions, such as the perception of the self and the conscious awareness of one's own body, a possible link between SPSs and interoception has been advocated. Yet, no study has provided direct evidence on such a relationship. The aim of the present study was to establish a link between SPSs and interoception. On the basis of the literature, the accuracy of heartbeat perception was taken as an index of general interoception across different bodily modalities. It was found that individuals with good heartbeat perception experienced more numerous and more intense SPSs. Furthermore, taken along with other individual characteristics, heartbeat perception accuracy predicted the perceived intensity of SPSs, their spatial extent, their variety, as well as confidence in their spatial characteristics. However, we also provide evidence that good vs. poor heartbeat perception is not just a matter of degree. We conclude that interoception definitely contributes to the perception of SPSs.

Unconscious odor detection could not be due to odor itself.

Unconscious odor detection has been demonstrated but the mechanisms implied in this process have been poorly studied. In so far, most odorants activate both olfactory and trigeminal systems, it is relevant to explore how each system could be involved in the unconscious detection processes. This study used three methods to determine the detection thresholds for three odorants. The results showed that (1). psychophysical were lower than self-evaluated thresholds whatever the odorant; (2). an odorant with trigeminal component had the ability to produce an autonomic (skin conductance response-SCR) activation with lower concentrations than psychophysical and self-evaluated thresholds; on the contrary, an odorant, which stimulates only the olfactory system, induces an autonomic activation only with higher concentrations than psychophysical and self-evaluated thresholds. These findings suggest that unconscious odor detection could be due to the trigeminal component of odorants.

Ambient odors modulate visual attentional capture.

Sudden visual events capture attention involuntarily because they may signal potential threats. Some theoretical accounts consider that the biological significance of these events is established through the limbic structures. Thus, the manipulation of the limbic activity would affect attentional capture. Since these structures are directly linked to the olfactory system, we have tended to modulate their activity with olfactory stimulations. We have examined behavioral performance in a task of attentional capture by luminance under conditions of ambient odors. Our results show that attentional capture is indeed modulated by ambient odors, and that this modulation may depend on the odor's properties.

Influence of nasal trigeminal stimuli on olfactory sensitivity.

In the nose, the capacity to detect and react to volatile chemicals is mediated by two separate but interrelated sensory pathways, the olfactory and trigeminal systems. Because most chemosensory stimulants, at sufficient concentration, produce both olfactory and trigeminal sensations (i.e., stinging, burning or pungent), it is relevant to seek how these anatomically distinct systems could interact. This study was designed to evaluate by psychophysical measurements the modifications of the olfactory sensitivity of 20 subjects to phenyl ethyl alcohol (PEA) and butanol (BUT), after trigeminal stimulation with allyl isothiocyanate (AIC). Thresholds obtained in two separate sessions, one with and the other without previous trigeminal stimulation, were compared using a two-alternative forced-choice procedure, with a classical ascending concentrations method. The results showed that, whatever the odorant (PEA or BUT), AIC trigeminal activation produced a decrease in the olfactory thresholds, corresponding to an increase in olfactory sensitivity. These data confirm that in physiological conditions the trigeminal system modulates the activity of olfactory receptor cells but do not exclude the possibility of a central modulation of olfactory information by trigeminal stimuli. These findings are discussed in terms of methodological and physiological conditions.

Left:right differences in psychophysical and electrodermal measures of olfactory thresholds and their relation to electrodermal indices of hemispheric asymmetries.

The study of lateralization processes in olfaction in human subjects has given rise to many contradictory findings. Indeed, sensorial cerebral asymmetry in olfaction depends on several factors (nature of task, quality of stimulus, characteristics of subjects, etc.) and could be also related to differences between the nostrils. In this field, few studies have assessed simultaneously the left-right nostril differences and the hemispheric asymmetry. The present work dealt with this question in the same population with the same odorants, procedures, and stimulations. Seven different concentrations of four specific odorants (two pleasant and two unpleasant) were used by single nostril stimulation with 30 dextral subjects (20 women and 10 men). Threshold detection in unilateral stimulation was investigated using electrodermal response to confirm the first psychophysic measure. Moreover, bilateral recordings of electrodermal activity (EDA) with unilateral stimulation were used as a measure of functional hemispheric asymmetry. Analysis showed no differences between the two nostrils for the threshold detection regardless of the method used (psychophysic or EDA response). However, most subjects presented a constant direction of electrodermal asymmetry whichever nostril was stimulated and whichever odorant stimulus used. The constant bilateral differences in EDA recordings are discussed in terms of asymmetrical activation of the hemispheres.

Transitivity of odor preferences: constant and particularities in hedonic perception.

Transitivity of preferences has been investigated for a long time in decision-making. In the field of perception, the pleasantness of odors raises several questions related to individual versus cultural or universal preferences and the existence of a classification in a delimited hedonic space. The aim of this study was to test transitivity in olfactory hedonicity using a first panel of 10 mixed odors and a second panel of 10 odors from a delimited floral category. Data were collected by paired comparisons in a two-alternative forced choice. Results in both panels showed a strong transitivity for each participant leading to a linear range of 10 odors classified by preference. However, ranges varied from one participant to another and the mean preferences of the group did not allow one to infer individual's hedonic classification of odors. Moreover, the individual classification appeared stable over time and undisturbed by odorant distractors. These findings suggest that humans have considerable ability to classify odors hedonically as a model of individual preferences in a sensory space usually considered to be more involved in affective/emotional states than in cognitive performances.

Comparative Fear-Related Behaviors to Predator Odors (TMT and Natural Fox Feces) before and after Intranasal ZnSO(4) Treatment in Mice.

The possibility that synthetic 2,4,5-trimethylthiazoline (TMT), frequently used to induce unconditioned fear in rodents, could be more a pungent odor activating intranasal trigeminal nerve fibers rather than a predator odor index is currently discussed. In order to explore this question, the present study compared fear-related behaviors to predator odors (synthetic 10% TMT and natural fox feces) and toluene (as an irritant compound without ecological significance) before and after intranasal ZnSO(4) perfusion which is known to provoke transient anosmia. Results show that natural fox feces could be consider as a pure olfactory (CN I) nerve stimulant while 10% TMT appeared to be a mixed olfactory (CN I) and trigeminal (CN V) nerves stimulant with a great olfactory power and a low trigeminal power. These findings suggest that behavioral neuroscience studies should use concentrations lower than 10% TMT to obtain fear-related behaviors similar to those obtained with natural fox feces odor.

Sensitization and desensitization to allyl isothiocyanate (mustard oil) in the nasal cavity.

The aim of this study was to investigate the response, acute effects and time-course of sensitization and desensitization to allyl isothiocyanate (mustard oil) nasal stimuli in healthy subjects. Sixty subjects participated in the experiment, which employed psychophysical (intensity ratings) and psychophysiological (skin conductance response) measurements. Nasal stimuli were delivered three times with different inter-stimulus intervals. The results showed that the psychophysical and psycho-physiological data were correlated and that the successive nasal stimuli after a short period of time (<2 min) produced increased intensity of irritation, whereas the stimuli delivered after >3 min produced a markedly decreased intensity of irritation. These findings are in agreement with those obtained with capsaicin, the most frequently used irritant molecule.