Odor Stimuli Research Articles

ABA, AAB and ABC renewal with Pavlovian Conditioning of Tentacle Lowering procedure in the snail Cornu aspersum

This study assesses the recovery of the conditioned response (CR) due to a contextual change (renewal effect) in the Cornu aspersum, using the appetitive Pavlovian Conditioning of Tentacle Lowering procedure. Snails experienced an odorous conditioned stimulus (CS) paired with food (conditioning), followed by the exposition to the CS without any consequence (extinction). Then, they were exposed to the CS in a different context from the extinction one (renewal test). The contexts were three types of illumination. In Experiment 1a, the conditioning was performed in context A, the extinction was conducted in context B and the renewal test was performed in context A. For Experiment 1b, the conditioning and extinction were conducted in context A and renewal was performed in context B. In Experiment 1c, three dissimilar contexts were used for each experimental phase: context A for the conditioning, context B for the extinction and context C for the renewal. In Experiment 2, the renewal magnitude was compared among the three paradigms (ABA, AAB and ABC). Experiments 1a, 1b and 1c showed a recovery of the CR when subjects experienced a contextual change and Experiment 2 showed equivalent levels of renewal in the three paradigms. Learning processes and theories involved are discussed.

Olfactory stimulus as environmental enrichment for shelter dogs: a pilot study

Environmental enrichment techniques include olfactory stimuli for improving animal welfare. This study aimed to analyze the reactions of 41 shelter dogs exposed to odorous stimuli, such as the method used in another study on wild canids. The focal animal method analyzed the dogs’ reactions, with all behaviors recorded. Behavioral responses were classified as positive (P+), negative (N-), or other (Ot). Independent variables were all dogs and the size of the packs. The behavior between the basal (without stimulus), exposure, and after-stimulus withdrawal was analyzed. For all dogs, olfactory stimuli significantly increased P+ (P=0.001) and N- (P=0.004), contrasting with the decrement of Ot behaviors (P=0.001) from the basal to the exposure phase. After the withdrawal of the stimuli, P+, N-, and Ot behaviors returned to basal levels (P>0.05). There were no significant differences (P>0.05) in the conduct of small or large packs exposed to stimuli. Dogs are sensitive to olfactory stimuli, but arousal is generalized to P+ and N-. It is undesirable to an N- increase for improvement of animal welfare. Contrary to what was observed in a study with wild canids, the method failed in shelter dogs because N- was increased. The introduction of sudden novelty (olfactory stimulus) in an impoverished shelter environment may have caused excitement in the dogs. It is suggested that changes in the method, such as stimuli exposition to each dog in an isolated room, are necessary to increase sheltered dog well-being.

Building a Uniport Olfactometer to Assess Mosquito Responses to Odors.

The uniport olfactometer behavioral assay is currently one of the most reliable single-choice methods to use to study mosquito attraction to olfactory stimuli. It allows for the reproducible calculation of mosquito attraction rate to human hosts or to other olfactory stimuli. Here, we present the design of our modified uniport olfactometer. Consistent carbon-filtered air flows through the assay, creating positive pressure that reduces odor contamination from the room. It includes a precision-milled white acrylic base to facilitate easy setup and consistent placement of the component parts. Our design can be made by a commercial acrylic fabricator or an academic machine shop. This olfactometer is designed to assess the responses of mosquitoes but could be applied to other insects that fly upwind toward an odor stimulus. In a companion protocol, we detail how to perform the experiments with mosquitoes by using the uniport olfactometer.

Episodic Odor Recognition Memory Is Reflected in Narratives About the Earliest Memories in Older Adults

Abstract Many studies have shown that the characteristics of odor-evoked memories differ from the characteristics of memories evoked by other senses. So far, no research has specifically investigated the relationship between odor memory and the quality of memories without using an odor trigger. The purpose of this study was to explore the link between episodic odor recognition memory and the linguistic and semantic content of autobiographical narratives about the earliest memories of older adults by a methodological approach deprived of odor stimuli. A sample of 112 older adults aged 59 to 101 years old was recruited. Odor memory was measured via the Sniffin’ Test of Odor Memory, and the linguistic and semantic content of memories was measured via the Linguistic Inquiry and Word Count system. The results showed that episodic odor recognition memory was a predictor of the number of first-person pronouns and number of words concerning cognitive processes in the narratives about the earliest memories. Implications for memory and future research directions are discussed.

Odorimetric indicators of substances and their ability to cause emotional “annoyance”

Introduction. The aim of the study was to analyze the quantitative relationship between the perceived intensity of the odours and its “offensiveness” (“annoyance potential”) in experimental organoleptic studies using the example of various perfumery aromatic compositions.
 Materials and methods. Experimental studies were carried out on the example of 22 perfume compositions (aromatic fragrances) used in the production of perfumery and cosmetic products. In total, 440 odorimetric measurements were carried out as part of the experiment. Statistical processing of the obtained data was carried out using the software Statistica for windows “StatSoft’ v. 7.0.
 Results. The linear association was revealed (R = 0.844; p = 0.0000008) between the perceived intensity of the aromatic compositions’ odour and its offensiveness (“annoyance potential”), defined as the percentage of positive responses; and the moderate linear association (R = 0.472; p=0.026) between the intensity of the odour and the sense of annoyance caused thereby, expressed in points. At the same time, a subjective assessment of the odour as annoying increases the likelihood of a higher assessment of its intensity.
 Limitation. The limitations of this study are associated with a relatively small number of participants, as well as the use of a relatively new method for recording the effects of odour stimuli, which requires additional testing.
 Conclusion. The intensity of the perceived odour was established to be an indicator that reflects not only its strength (concentration), but also a subjective attitude to it, reliably reflecting the degree of annoyance (feeling of “offensiveness”) by the odour present in the air, and, accordingly, can be taken as a base for establishing air quality criteria by odour in the environment.
 Keywords: odour intensity; “offensiveness” of the odour; “annoyance potential”; organoleptic studies; odorimetry; aromatic compositions 
 Compliance with ethical standards. The consent of the local ethics committee of the Centre for Strategic Planning of FMBA of Russia was obtained for the conduct of the research (protocol No. 3 dated August 17, 2020).
 Patient consent. Each participant of the study (or his/her legal representative) gave informed voluntary written consent to participate in the study and publish personal medical information in an impersonal form in the journal "Gigiena i Sanitariya (Hygiene and Sanitation, Russian journal)".

Characterization of olfactory sensory neurons in the striped ambrosia beetle Trypodendron lineatum.

Introduction: The striped ambrosia beetle Trypodendron lineatum (Coleoptera, Curculionidae, Scolytinae) is a major forest pest in the Holarctic region. It uses an aggregation pheromone and host and non-host volatiles to locate suitable host trees, primarily stressed or dying conifer trees. The beetles bore into the xylem and inoculate spores of their obligate fungal mutualist Phialophoropsis ferruginea inside their excavated egg galleries, with the fungus serving as the main food source for the developing larvae. Olfactory sensory neuron (OSN) responses to pheromones and host volatiles are poorly understood in T. lineatum and other ambrosia beetles, and nothing is known about potential responses to fungal volatiles. Methods: We screened responses of OSNs present in 170 antennal olfactory sensilla using single sensillum recordings (SSR) and 57 odor stimuli, including pheromones, host and non-host compounds, as well as volatiles produced by P. ferruginea and fungal symbionts of other scolytine beetles. Results and Discussion: Thirteen OSN classes were characterized based on their characteristic response profiles. An OSN class responding to the aggregation pheromone lineatin was clearly the most abundant on the antennae. In addition, four OSN classes responded specifically to volatile compounds originating from the obligate fungal mutualist and three responded to non-host plant volatiles. Our data also show that T. lineatum has OSN classes tuned to pheromones of other bark beetles. Several OSN classes showed similar response profiles to those previously described in the sympatric bark beetle Ips typographus, which may reflect their shared ancestry.

Trigeminal stimulation is required for neural representations of bimodal odor localization: A time-resolved multivariate EEG and fNIRS study

Whereas neural representations of spatial information are commonly studied in vision, olfactory stimuli might also be able to create such representations via the trigeminal system. We explored in two independent multi-method electroencephalography–functional near-infrared spectroscopy (EEG+fNIRS) experiments (n1=18, n2=14) if monorhinal odor stimuli can evoke spatial representations in the brain. We tested whether this representation depends on trigeminal properties of the stimulus, and if the retention in short-term memory follows the “sensorimotor recruitment theory”, using multivariate representational similarity analysis (RSA). We demonstrate that the delta frequency band up to 5 Hz across the scull entail spatial information of which nostril has been stimulated. Delta frequencies were localized in a network involving primary and secondary olfactory, motor-sensory and occipital regions. RSA on fNIRS data showed that monorhinal stimulations evoke neuronal representations in motor-sensory regions and that this representation is kept stable beyond the time of perception. These effects were no longer valid when the odor stimulus did not sufficiently stimulate the trigeminal nerve as well. Our results are first evidence that the trigeminal system can create spatial representations of bimodal odors in the brain and that these representations follow similar principles as the other sensory systems.

An optofluidic platform for interrogating chemosensory behavior and brainwide neural representation in larval zebrafish

Studying chemosensory processing desires precise chemical cue presentation, behavioral response monitoring, and large-scale neuronal activity recording. Here we present Fish-on-Chips, a set of optofluidic tools for highly-controlled chemical delivery while simultaneously imaging behavioral outputs and whole-brain neuronal activities at cellular resolution in larval zebrafish. These include a fluidics-based swimming arena and an integrated microfluidics-light sheet fluorescence microscopy (µfluidics-LSFM) system, both of which utilize laminar fluid flows to achieve spatiotemporally precise chemical cue presentation. To demonstrate the strengths of the platform, we used the navigation arena to reveal binasal input-dependent behavioral strategies that larval zebrafish adopt to evade cadaverine, a death-associated odor. The µfluidics-LSFM system enables sequential presentation of odor stimuli to individual or both nasal cavities separated by only ~100 µm. This allowed us to uncover brainwide neural representations of cadaverine sensing and binasal input summation in the vertebrate model. Fish-on-Chips is readily generalizable and will empower the investigation of neural coding in the chemical senses.

Effects of proactive interference on olfactory memory in dogs.

Proactive interference (PI) occurs when memories of past events or stimuli intrude in the present moment, causing working memory (WM) errors. These errors are often measured through WM tests such as matching-to-sample (MTS). When the repetition of individual stimuli increases, there is a greater chance of these intrusions, and thus there can be a decrease in accuracy in such tasks. In two experiments, we explored the nature of PI on dog working memory. First, we manipulated the size of the set of odors (2, 6, trial-unique) used to construct each session to maximize (2-odor set) and minimize (trial-unique) within-session proactive interference during an olfactory MTS task. Matching-to-sample accuracy decreased with greater PI. Second, we adapted procedures originally designed for pigeons and rhesus macaques to determine the locus of PI in dogs. To test for proactive interference, probe trials were inserted into MTS sessions where sample odors from earlier trials reappeared as incorrect comparisons. Incorrect responses on these probe trials indicated proactive interference. These probe tests were conducted with a 0-s or 20-s retention interval in separate sessions. We found that dogs performed worse on the matching task when the source of interference (odor stimulus) was from the immediately preceding trial compared with when they were from trials further back in the session but only for the 0-s retention interval. These results are compared with previous work examining the effects of proactive interference on working memory in other species.

Improvement of olfactory fMRI activation and hemodynamic response function curve with respiration correction

BackgroundOdor perception is highly dependent on respiration, however, the asynchronization between inspiration and odor delivery results in a decreased activation and hemodynamic response function (HRF) curve in olfactory functional MRI (fMRI). This study aimed to investigate the effect of a data post-processing method to minimize the asynchronization and consequently improve the olfactory activation and HRF curve and compare it between different TRs (3 s and 1 s). New methodA new data post-processing method of respiration correction based on olfactory perception was investigated. Comparison with existing methodsThe odor stimuli of olfactory fMRI were mostly based on odor deliveries. But for the reason of respiration, the time of olfactory perception might be a little different. The actual onset time and duration of odor stimuli were modified based on the respiration data. ResultsFor 3 s TR data, an increased number of activated voxels and higher HRF curves response height were obtained with the respiration correction method in the primary olfactory cortex (POC) (P = 0.034 and 0.009) and insula (P = 0.024 and 0.001), compared with the uncorrected method. But the activated voxels and response height of the anterior cingulate cortex (ACC) did not differ between uncorrected and respiration correction methods (P = 0.102 and 0.200). The time to peak of the HRF curve was shorter with the respiration correction method in all ROIs (all P < 0.05), compared with the uncorrected method. Whereas there were no significant differences between the uncorrected and corrected results for 1 s TR data. ConclusionsThe post-processing method of respiration correction could effectively minimize the asynchronization between respirations and odor deliveries, and improve the activations and HRF curves for a routine 3 s TR olfactory fMRI data.

Electrophysiological Recordings from Identified Cell Types in the Olfactory Cortex of Awake Mice.

Neural circuits consist of a myriad of distinct cell types, each with specific intrinsic properties and patterns of synaptic connectivity, which transform neural input and convey this information to downstream targets. Understanding how different features of an odor stimulus are encoded and relayed to their appropriate targets will require selective identification and manipulation of these different elements of the circuit. Here, we describe methods to obtain dense, extracellular electrophysiological recordings of odor-evoked activity in olfactory (piriform) cortex of awake, head-fixed mice, and optogenetic tools and procedures to identify genetically defined cell types within this circuit.

Sensory Evaluation of Interference Suppression in Odor Reproduction Using Mass Spectrometry

Odor sensing enables us to sense odorant stimuli. This sensation causes a deep subconscious response in humans in various ways and represents an indispensable sensation in daily life. However, unwanted compounds called fixatives, which can cause a contradiction in odorant analysis especially between mass spectrometry and human subject, are included in odorant samples. Moreover, we do not know the pure odorant mass spectrum. Therefore, it is essential to eliminate the interference of fixatives from the odor sample mass spectrum data and to extract the pure odor mass spectrum. In the present study, we performed independent component analysis (ICA) on the mass spectra of odor samples to remove the influence of fixatives. The advantage of the ICA in separating independent components without a priori knowledge of the original data is useful. The abundance of essential-oil mass spectra that we gathered were utilized as odorant samples. The results were compared with sensory test data from a human subject for a better study of fixative influence. It was revealed that ICA could extract the pure odor sample mass spectrum data without the influence of fixatives, even if the fixatives were added to the odor samples. This study’s outcomes allow us to analyze more odor samples for odorant analysis, not hindered by the influence of unwanted compounds.

Estimating the relationship between liquid- and vapor-phase odorant concentrations using a photoionization detector (PID)-based approach.

Olfactory studies frequently utilize odor stimuli consisting of volatiles created from liquid dilutions of various chemicals. A problem arises if the researcher relies on these liquid dilutions to extrapolate vapor concentrations based on ideal gas behavior. For most chemicals, the relationship between liquid and vapor concentration deviates from these laws of proportionality due to interactions between the chemical and the solvent. Here, we describe a method to estimate vapor-phase concentrations of diluted odorants using a photoionization detector. To demonstrate the utility of this method, we assessed the relationship between liquid-/vapor-phase concentrations for 14 odorants (7 alcohols, 1 ester, and 6 aldehydes) in 5 different solvents (water, mineral oil, diethyl phthalate, dipropylene glycol, and propylene glycol). An analysis of 7 additional esters is also included to assess how carbon chain length and functional group, interacts with these solvents (for a total of 105 odorant/solvent pairs). Our resulting equilibrium equations successfully corrected for behavioral sensitivity differences observed in mice tested with the same odorant in different solvents and were overall similar to published measurements using a gas chromatography-based approach. In summary, this method should allow researchers to determine the vapor-phase concentration of diluted odorants and will hopefully assist in more accurate comparisons of odorant concentrations across olfactory studies.

Multisensory integration of orally-sourced gustatory and olfactory inputs to the posterior piriform cortex in awake rats.

Flavour refers to the sensory experience of food, which is a combination of sensory inputs sourced from multiple modalities during consumption, including taste and odour. Previous work has demonstrated that orally-sourced taste and odour cues interact to determine perceptual judgements of flavour stimuli, although the underlying cellular- and circuit-level neural mechanisms remain unknown. We recently identified a region of the piriform olfactory cortex in rats that responds to both taste and odour stimuli. Here, we investigated how converging taste and odour inputs to this area interact to affect single neuron responsiveness ensemble coding of flavour identity. To accomplish this, we recorded spiking activity from ensembles of single neurons in the posterior piriform cortex (pPC) in awake, tasting rats while delivering taste solutions, odour solutions and taste+odour mixtures directly into the oral cavity. Our results show that taste and odour inputs evoke highly selective, temporally-overlapping responses in multisensory pPC neurons. Comparing responses to mixtures and their unisensory components revealed that taste and odour inputs interact in a non-linear manner to produce unique response patterns. Taste input enhances trial-by-trial decoding of odour identity from small ensembles of simultaneously recorded neurons. Together, these results demonstrate that taste and odour inputs to pPC interact in complex, non-linear ways to form amodal flavour representations that enhance identity coding. KEY POINTS: Experience of food involves taste and smell, although how information from these different senses is combined by the brain to create our sense of flavour remains unknown. We recorded from small groups of neurons in the olfactory cortex of awake rats while they consumed taste solutions, odour solutions and taste+odour mixtures. Taste and smell solutions evoke highly selective responses. When presented in a mixture, taste and smell inputs interacted to alter responses, resulting in activation of unique sets of neurons that could not be predicted by the component responses. Synergistic interactions increase discriminability of odour representations. The olfactory cortex uses taste and smell to create new information representing multisensory flavour identity.

Olfactory coding

Modern humans live in real and digital environments dominated by sight and sound, but the vast majority of organisms on the planet rely on information received through air- or water-borne molecules to find food, avoid danger, and reproduce. Olfaction is at once both the primitive sensory modality and one of the hardest to understand, in large part due to the complexity of olfactory stimulus space. Whereas light and sound are easily ordered along natural physical axes that are reflected in their respective sensory codes, the organizational axes of odor space are not obvious. The search for systematic relationships between physicochemical characteristics of monomolecular odorants (carbon chain length, bond numbers, functional groups, etc.) and human perception of odorants suggests that olfactory perceptual space is a relatively low-dimensional structure. Odor descriptors provided by human observers are often significantly correlated. For instance, odors perceived as 'woody' are also likely to be described as 'warm', and many studies converge on hedonic valence or 'pleasantness' as being one of the most important dimensions of how people perceive odors. The identification of additional perceptual 'primaries' around which olfaction is organized is an active area of investigation, and a useful account of olfactory coding must explain this transformation of odor stimuli from the high dimensional chemical space to a lower dimensional perceptual space.

Physiological and Behavioral Characterization of Larval Olfaction in the Malaria Vector Mosquito Anopheles coluzzii.

When viewed from both academic and vector-control perspectives, the chemosensory biology of larval-stage anopheline mosquitoes is both enigmatic and paradoxical. As is true for all mosquito species, anopheline larvae are free-swimming organisms that use complex sensory processes to both locate nutrients and avoid predators. Because of their obligatory and therefore restrictive aquatic habitats, mosquito larvae are the most easily sampled and targeted mosquito life stage and as such they have been the focus of the majority of vector control strategies used to date. Although this might reasonably have resulted in the accumulation of a robust body of knowledge of the natural and molecular biology of larval-stage chemosensory processes, there is, instead, a paucity of such information relative to adults. Here, we describe two relatively simple laboratory-based bioassays that allow for the characterization of larval chemosensory-driven behaviors as well as an electrophysiological approach to examine the responses of larval peripheral neurons to volatile odorant stimuli. Taken together, these approaches provide a road map for the study of the chemosensory biology and chemical ecology during this important stage in the life cycle of anophelines that transmit malaria.

A multivesicular body-like organelle mediates stimulus-regulated trafficking of olfactory ciliary transduction proteins

Stimulus transduction in cilia of olfactory sensory neurons is mediated by odorant receptors, Gαolf, adenylate cyclase-3, cyclic nucleotide-gated and chloride ion channels. Mechanisms regulating trafficking and localization of these proteins in the dendrite are unknown. By lectin/immunofluorescence staining and in vivo correlative light-electron microscopy (CLEM), we identify a retinitis pigmentosa-2 (RP2), ESCRT-0 and synaptophysin-containing multivesicular organelle that is not part of generic recycling/degradative/exosome pathways. The organelle’s intraluminal vesicles contain the olfactory transduction proteins except for Golf subunits Gγ13 and Gβ1. Instead, Gβ1 colocalizes with RP2 on the organelle’s outer membrane. The organelle accumulates in response to stimulus deprivation, while odor stimuli or adenylate cyclase activation cause outer membrane disintegration, release of intraluminal vesicles, and RP2/Gβ1 translocation to the base of olfactory cilia. Together, these findings reveal the existence of a dendritic organelle that mediates both stimulus-regulated storage of olfactory ciliary transduction proteins and membrane-delimited sorting important for G protein heterotrimerization.

Spike frequency adaptation facilitates the encoding of input gradient in insect olfactory projection neurons

The olfactory system in insects has evolved to process the dynamic changes in the concentration of food odors or sex pheromones to localize the nutrients or conspecific mating partners. Experimental studies have suggested that projection neurons (PNs) in insects encode not only the stimulus intensity but also its rate-of-change (input gradient). In this study, we aim to develop a simple computational model for a PN to understand the mechanism underlying the coding of the rate-of-change information. We show that the spike frequency adaptation is a potential key mechanism for reproducing the phasic response pattern of the PN in Drosophila. We also demonstrate that this adaptation mechanism enables the PN to encode the rate-of-change of the input firing rate. Finally, our model predicts that the PN exhibits the intensity-invariant response for the pulse and ramp odor stimulus. These results suggest that the developed model is useful for investigating the coding principle underlying olfactory information processing in insects.

Effects of predator odor on anti-predation behavior and hypothalamic c-fos mRNA expression of Chinese mole shrew

Chinese mole shrew (Anourosorex squamipes, Soricidae) is a small mammal, with a large population in the low mountain basin area of Sichuan, China, and it is one of the main pests in farmland. We exposed A. squamipes to cat（a natural predator） and rabbit（a non-natural predator） odors, and compared their behaviors and hypothalamus c-fos mRNA expression. This paper explored the behavioral changes in predator odor stress of A. squamipes, which reveals the shrews’ stress response mechanism to natural predators. In this study, 36 Chinese mole shrew individuals were exposed to different odors for a short time (10 min) under laboratory conditions. Distilled water was used as the control group (CG), rabbit urine odor as the non-predator group (NG), and cat urine odor as the predator group (PG). SuperMaze animal behavior video analysis system was used to observe and record anti-predation behavior data. The real-time fluorescence quantitative nucleic acid amplification detection system (QPCR) was used to determine the expression of hypothalamic c-fos genes. The results showed that 1) both male and female shrews were significantly stimulated by cat odor, and their time of concealment, sniffing, wariness, and escape behavior showed significant increases, showing that the shrews responded strongly to the odors of a natural predator and showed clear anti-predation behavior. 2) different odor stimuli resulted in different expression of c-fos mRNA in the shrews’ hypothalamus, and there was no significant difference between the rabbit odor treatment group and that of the control group. The expression of c-fos mRNA in the cat odor was significantly higher than other two groups, indicating that the stress response of A. squamipes to natural predator is closely related to the expression of c-fos mRNA. The result shows that A. squamipes can recognize the scent of predators and regulate their own behavior by promoting the expression of c-fos mRNA in the hypothalamus, thereby increasing the investment into anti-predation defense strategies.

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…).