Multidimensional representation of odors in the human olfactory cortex.

What is known as an odor object is an integrated representation constructed from physical features, and perceptual attributes mainly mediated by the olfactory and trigeminal systems. The aim of the present study was to comprehend how this multidimensional representation is organized, by deciphering how similarities in the physical, olfactory and trigeminal perceptual spaces of odors are represented in the human brain. To achieve this aim, we combined psychophysics, functional MRI and multivariate representational similarity analysis. Participants were asked to smell odors diffused by an fMRI-compatible olfactometer and to rate each smell along olfactory dimensions (pleasantness, intensity, familiarity and edibility) and trigeminal dimensions (irritation, coolness, warmth and pain). An event-related design was implemented, presenting different odorants. Results revealed that (i) pairwise odorant similarities in anterior piriform cortex (PC) activity correlated with pairwise odorant similarities in chemical properties (P < 0.005), (ii) similarities in posterior PC activity correlated with similarities in olfactory perceptual properties (P <0.01), and (iii) similarities in amygdala activity correlated with similarities in trigeminal perceptual properties (P < 0.01). These findings provide new evidence that extraction of physical, olfactory and trigeminal features is based on specific fine processing of similarities between odorous stimuli in a distributed manner in the olfactory system. Hum Brain Mapp 37:2161-2172, 2016. © 2016 Wiley Periodicals, Inc.

Application of the European Test of Olfactory Capabilities in patients with olfactory impairment.

A central issue in olfaction concerns the characterization of loss of olfactory function: partial (hyposmia) or total (anosmia). This paper reports the application in a clinical setting of the European Test of Olfactory Capabilities (ETOC), combining odor detection and identification. The study included three phases. In phase 1, anosmics, hyposmics and controls were tested with the 16-items version of the ETOC. In phase 2, a short version of the ETOC was developed: patients with and controls without olfactory impairment were tested on a 6-items ETOC. In phase 3, to predict olfactory impairments in new individuals, the 16-items ETOC was administered on samples of young and older adults, and the 6-items version was applied in samples of young, elderly participants and Alzheimer patients. In phase 1, linear discriminant analysis (LDA) of ETOC scores classified patients and controls with 87.5 % accuracy. In phase 2, LDA provided 84 % correct classification. Results of phase 3 revealed: (1) 16-items ETOC: whereas in young adults, 10 % were classified as hyposmic and 90 % as normosmic, in elderly, 1 % were classified as anosmic, 39 % hyposmic and 60 % normosmic; (2) 6-items ETOC: 15 % of the young adults were classified as having olfactory impairment, compared to 28 % in the older group and 83 % in Alzheimer patients. In conclusion, the ETOC enables characterizing the prevalence of olfactory impairment in young subjects and in normal and pathological aging. Whereas the 16-items ETOC is more discriminant, the short ETOC may provide a fast (5-10 min) tool to assess olfaction in clinical settings.

Does olfactory specific satiety take place in a natural setting?

Olfactory-specific satiety (OSS) is characterized by a specific decrease in the odor pleasantness of a food eaten to satiety or smelled without ingestion. The usual protocol for studying OSS takes place in laboratory, a setting rather removed from the real world. Here, we set out to examine OSS in a natural setting: during a meal in a restaurant. We hypothesized that an aroma contained in a food that is eaten at the beginning of a meal decreases the pleasantness of the flavor of a food with the same aroma eaten at the end of the meal. In the first experiment (Experiment 1), a test group received an appetizer flavored with a test aroma (anise) at the beginning of the meal. After the main dish, they received a dessert flavored with the same aroma. A control group received the same aromatized dessert, but after a non-aromatized appetizer. This experiment was replicated (Experiment 2) using verbena as the test aroma. For both experiments, results revealed that aroma pleasantness, but not intensity or familiarity, significantly decreased in the test groups vs. the control groups. These findings extend the concept of OSS to a realistic eating context.

Molecular complexity determines the number of olfactory notes and the pleasantness of smells.

One major unresolved problem in olfaction research is to relate the percept to the molecular structure of stimuli. The present study examined this issue and showed for the first time a quantitative structure-odor relationship in which the more structurally complex a monomolecular odorant, the more numerous the olfactory notes it evokes. Low-complexity odorants were also rated as more aversive, reflecting the fact that low molecular complexity may serve as a warning cue for the olfactory system. Taken together, these findings suggest that molecular complexity provides a framework to explain the subjective experience of smells.

Development of olfactory ability in children: sensitivity and identification.

This study assessed the influence of school level and gender on odor sensitivity and identification, and the role of verbal capacity on odor identification in children (4-12 years) by using a revised version of an olfactory test designed for adults [Rouby et al. (1997). Connaissance et reconnaissance d'une série olfactive chez l'enfant préscolaire. Enfance, 1, 152-171]. We found that odor sensitivity and identification scores increased with school level, and that identification performance was better in girls than in boys. However, when we controlled verbal ability, the gender differences disappeared and the school level differences remained. This result indicates that the effect of gender on identification was probably due to the greater verbal ability of girls rather than to their greater olfactory ability per se. In addition, we found that general verbal ability is independent of olfactory fluency and that their influence on olfactory perception is different. Thus, this study illuminates the role of cognitive/verbal factors in the development of odor perception and knowledge.

Synergy and masking in odor mixtures: an electrophysiological study of orthonasal vs. retronasal perception.

Perceptual interactions in a model of wine woody-fruity binary mixtures were previously reported in a psychophysical study performed through orthonasal stimulation only. However, recent studies suggested that the perception of food-like and nonfood-like odors may depend on the route of stimulation. The aim of the present study was two-fold: first to examine the neural correlates of perceptual interactions using electroencephalogram (EEG)-derived event-related potentials (ERPs) and second to test the influence of the stimulation route on quality perception. Therefore, we designed an experiment with 30 subjects to study perceptual interactions in woody-fruity mixtures and compared ortho- vs. retronasal stimulation sites on perceived odor quality and ERPs. The results revealed synergy or masking of the fruity component, depending on the woody component level. Synergy was supported by larger N1 amplitude of the ERP. Furthermore, mixtures including a medium level of the woody odor elicited a strong increase of P2 amplitude only retronasally. This study evidenced for the first time electrophysiological correlates of both perceptual synergy and masking on the early component of the ERPs and confirmed that retro- vs. orthonasal stimulation route induces different neural processes that are reflected in the late component of the ERP.

Improved smell pleasantness after odor-taste associative learning in humans.

Whereas some aspects of olfactory hedonism in humans are present from birth, others form during development and throughout adulthood. Although it is generally agreed that such hedonic representations emerge by associative learning, it is not yet clear which learning parameters are prominent. The present study investigated the influence of number of trials on odor preference acquisition in human adults. Forty-eight subjects randomly assigned to three groups were tested in three sessions. In the first session, subjects ranked eight food odors from most pleasant to most unpleasant. The second session consisted in an associative learning, the two most neutral odors were randomly associated with a drink: one odor with water (CS-) and the other odor with a pleasant sweet solution (CS+). In the third session subjects ranked the eight food odors again. In group A, CS+ was paired three times with the US, and in group B only once; in group C, CS+ was paired only once with the US but with a total duration identical to that in group A. Results showed that CS+ was ranked as significantly more pleasant after learning in group A (p<.05), but not in groups B and C (p>.05). In conclusion, the study showed that a neutral smell can acquire positive emotional features after being paired with a pleasant taste, and that this learning depends on the number of associations between smell and taste.

Individual differences in odor imaging ability reflect differences in olfactory and emotional perception.

We asked whether the large variability in odor imaging ability is underlain by interindividual differences in the processing of smells and emotion. Olfactory imaging ability, anhedonia level, and odor perception were measured in 40 subjects, using the Vividness of Olfactory Imagery Questionnaire (VOIQ), the Physical Anhedonia Scale, and the European Test of Olfactory Capabilities. "Good" olfactory imagers, defined primarily on the basis of the VOIQ, rated pleasant smells as more familiar and had lower anhedonia scores than "bad" olfactory imagers. Based on self-reported measures, these results suggest that, like olfactory perception, the mental imagery of smells is related to emotion and that, beyond their differences in vividness, good and bad olfactory imagers differ in their experience of emotion and long-term memory of smells.

Psychological and physiological evaluation of emotional effects of a perfume in menopausal women.

In the present study, we familiarized menopausal women with a pleasant smell in the skin care products, they used for 1 week and assessed whether their mood and emotions improved using behavioural and physiological tools. Eventually, we studied the effects of inhaling the familiar fragrance on physiological response of the subjects. An anhedonia questionnaire was used to distinguish the effects of the test products according to low vs. high score of anhedonia. Familiarization with the fragrance induced a modification of some physiological parameters, reflecting a relaxing effect, and these unconscious effects paralleled the conscious positive effects on mood recorded during the familiarization phase; it appeared that the effects were more prominent in subjects with higher scores of anhedonia. These results suggest that the pleasant smell of a skin care product contributes to the quality of life in a population of menopausal women with low easiness to experience pleasure.

[Practical measurement of radiation dose in pediatric radiology: use of the dose surface product in digital fluoroscopy and for neonatal chest radiographs]. / Mesure pratique de l'irradiation en radiopédiatrie: utilisation du produit dose surface en fluorographie numérique et pour les radiographies pulmonaires néonatales.

PURPOSE: Control of radiation dose in pediatric radiology requires knowledge of the reference levels for all examinations. These data are useful for daily quality assessment, but are not perfectly known for some radiographic examinations. The purpose of our study was to evaluate the dose related to voiding cystourethrograms (VCUG), upper GI (UGI) and intravenous urography (IVU). Neonatal chest radiographs in the intensive care unit were also evaluated. MATERIAL AND METHODS: For examinations with contrast material (478VCUG, 220UGI, 80IVU), the children were divided in groups based on their weight, from 5 to 30 Kg. Measurements were performed using an ionization chamber and expressed with the dose-area product (DAP). For chest radiographs, a direct measurement of the entrance-skin dose was performed, with secondary calculation of the DAP. RESULTS: For VCUGs, the DAP ranged between 42.89cGy.cm2 and 125.41cGy.cm2. The range was between 76.43 and 150.62cGy.cm2 for UGIs and between 49.06 and 83.33cGy.cm2 for IVUs. For neonate chest radiographs, DAP calculations were between 0.29 and 0.99cGy.cm2. CONCLUSION: These values represent our reference doses. They allow continuous monitoring of our radiographic technical parameters and radiographic equipment and help to correct and improve them if necessary.

Odor and color of cosmetic products: correlations between subjective judgement and autonomous nervous system response.

The color and odor of cosmetics have been shown to be crucial for affective states and able to influence autonomic responses. We report an original procedure to measure the effect on subjects of the color and odor of cosmetic products, and to quantify the correlation between objective (psychophysiological recording) and subjective (psychophysics) responses. Several cosmetic products (lipsticks and nail varnishes) of different colors (white, brown, red, orange, and pink) and odors (two per product) were presented. In a first step, autonomous parameters (skin conductance (SC) and heart rate (HR)) were recorded, and in the second step, subjects rated their sensations on subjective scales (overall appreciation, pleasantness, and emotional arousal). Results indicated that certain color and odor additives in cosmetics act on relaxation, excitation, perceived pleasantness, and emotional arousal. It was also found that certain colors, perceived as pleasant, decreased HR, and that the perception of an 'arousing' perfume significantly increased SC.

Psychophysiological correlates of affects in human olfaction.

Pleasantness and arousal have been identified as the main dimensions of affective responses to environment. Pleasantness is defined as the degree of favorable feelings a subject can experience under given circumstances. Arousal is defined as the degree of excitement (general activation) the subject feels under these circumstances. In visual and auditory modalities, many studies using measures such as facial electromyographic (EMG) activity and skin conductance (SC) have found those parameters to vary as a function of either pleasantness or arousal: for example, facial corrugator EMG activity covaries with the pleasantness dimension, while SC increases together with arousal. The first objective of this research is to study the possible covariation between peripheral measures and pleasantness/arousal in olfaction. We also examined the effect of odor intensity on facial and autonomic variations. The second objective was to investigate whether odors could evoke verbally specific emotions (e.g. joy, anger, fear, surprise, disgust or sadness) and also induce specific patterns of peripheral responses. Participants were exposed to 12 different odors while their facial and autonomic parameters were recorded, and estimated their intensity, pleasantness, and arousal capacity. Then, they chose between seven words for emotions (fear, anger, sadness, surprise, neutral, joy or disgust) to describe their reaction to the odor. As in vision, olfactory pleasantness covaries (negatively) with facial activity of the corrugator muscle, and arousal (positively) with skin conductance. No relationships were observed between physiological changes and variations in perceived intensity. Results also showed that emotions of "disgust" and "joy" were more frequently evoked verbally than any other emotions, and that only facial EMG activity distinguishes them (e.g. "disgust" vs. "joy" and "neutral state"). The results are discussed in terms of possible existence of two brain systems (defensive and appetitive), each of them being able to vary in metabolic arousal.

Autonomic nervous system responses to odours: the role of pleasantness and arousal.

Perception of odours can provoke explicit reactions such as judgements of intensity or pleasantness, and implicit output such as skin conductance or heart rate variations. The main purpose of the present experiment was to ascertain: (i) the correlation between odour ratings (intensity, arousal, pleasantness and familiarity) and activation of the autonomic nervous system, and (ii) the inter-correlation between self-report ratings on intensity, arousal, pleasantness and familiarity dimensions in odour perception. Twelve healthy volunteers were tested in two separate sessions. Firstly, subjects were instructed to smell six odorants (isovaleric acid, thiophenol, pyridine, L-menthol, isoamyl acetate, and 1-8 cineole), while skin conductance and heart rate variations were being measured. During this phase, participants were not asked to give any judgement about the odorants. Secondly, subjects were instructed to rate the odorants on dimensions of intensity, pleasantness, arousal and familiarity (self-report ratings), by giving a mark between 1 (not at all intense, arousing, pleasant or familiar) and 9 (extremely intense, arousing, pleasant or familiar). Results indicated: (i) a pleasantness factor correlated with heart rate variations, (ii) an arousal factor correlated with skin conductance variations, and (iii) a strong correlation between the arousal and intensity dimensions. In conclusion, given that these correlations are also found in other studies using visual and auditory stimuli, these findings provide preliminary information suggesting that autonomic variations in response to olfactory stimuli are probably not modality specific, and may be organized along two main dimensions of pleasantness and arousal, at least for the parameters considered (i.e. heart rate and skin conductance).

Asymmetry of pleasant vs. unpleasant odor processing during affective judgment in humans.

The objective of the present study was to investigate interactions between odor hedonic tone, perceived odor intensity, olfactory judgments and stimulated nostril laterality. Subjects were stimulated in the right and the left nostril separately, with two odors: vanillin (pleasant); and indole (unpleasant). They had two tasks to perform: an intensity judgment; and an affective judgment. Two concentrations (one strong and one weak) of each odor were presented. Odors were presented for a short period corresponding to one inhalation (about 1 s). The inter-stimulus interval was always 30 s. The nostril stimulated and task presentation order were counterbalanced according to a Latin square. Odor presentation order was randomized for each subject. Results indicated that response times for unpleasant odors were significantly shorter than for pleasant odors during affective judgment and right nostril stimulation, indicating greater right hemisphere efficiency for the decoding of unpleasant affects induced by odors.

Influence of affective and cognitive judgments on autonomic parameters during inhalation of pleasant and unpleasant odors in humans.

Hedonic tone is so salient in odor perception that several authors have used odors to induce affective states. Various studies have shown that the electrophysiological and psychophysiological response patterns induced by olfactory stimuli are different for pleasant and unpleasant odors, and that these types of odor activate brain structures differentially. These results suggest that odors are first categorized according to pleasantness. The objective of the present work was to study the possible existence of an involuntary affective categorization in olfaction. Given that certain variations in the autonomic system, such as skin conductance amplitude and heart rate, are not under the voluntary control of human subjects, we used such psychophysiological methods for this investigation. Our results indicate that unpleasant odors provoke heart-rate acceleration during both a smelling task (control condition: a task in which subjects had only to inhale odors) and a pleasantness judgment, but not during a familiarity judgment. These results suggest that subjects involuntarily categorize odors by their pleasantness.

Modulation of visual event-related potentials by emotional olfactory stimuli.

The objective of the present study was to determine whether an olfactory prime could modulate behavior and visual event-related potentials (ERPs) obtained in response to a visual stimulation representing female faces. More specifically, we tested the hypothesis that a pleasant odor could have effects on face perception: behavioral effects on subjective emotional estimation of faces, and on associated response times, and electrophysiological effects on the N400 and late positive complex or LPC. Experiments were performed in which subjects had to decide whether the presented face was pleasant or not, while visual ERPs were recorded. Faces were always primed with either a pleasant odor or a neutral olfactory stimulus (pure air). In order to test the effect of subject's awareness, participants were not informed that an odor would be presented in the experimental sessions. Responses were significantly shorter for unpleasant faces. However, no behavioral effects of the pleasant odor on response time or on evaluation of face pleasantness were observed. Late ERPs evoked by faces were modulated by the presence of a pleasant odor, even when subjects were neither warned nor aware of the presence of the odor: in a frontal site and after the diffusion of the odor, the LPC (appearing 550 ms after the presentation of the visual stimulus) evoked by unpleasant faces was significantly more positive than the LPC evoked by pleasant faces. This effect could reflect an enhanced alert reaction to unpleasant faces are preceded by an (incongrous) pleasant odor.

Neural mechanisms involved in odor pleasantness and intensity judgments.

Olfactory processing in the human brain was examined using positron emission tomography. Twelve normal volunteers were scanned while smelling pairs of odors: they were asked to judge which odor was more pleasant in one condition, and which was more intense in a second condition; they also were scanned while sniffing an odorless stimulus. As in prior studies, greater cerebral blood flow was found in the right orbitofrontal cortex during both pleasantness and intensity judgments as compared to baseline. Cerebellar activity was also seen, but contrary to expectations no activity was detected in the primary olfactory (piriform) cortex. Only the pleasantness judgment elicited additional activity within the hypothalamus, suggesting that this structure may be involved in affective processing that requires access to information about internal state.

Is short-term odour recognition predictable from odour profile?

Smelling an odour induces a pattern of sensations, images and memories which participate in identification. It was proposed that perceptual memory performances for odours could be inferred from the description of these olfactory representations. The subject was asked to elaborate an odour descriptor profile, and a short-term odour recognition memory task was chosen to test the individual perceptual memory performance. Two pattern-recognition methods based on artificial neural networks and discriminant analysis were carried out and allowed odour profile and perceptual memory performance to be related. Insofar as the subjects gave dichotomic responses in the recognition memory task, each response could be evaluated in terms of correct or incorrect responses. Simulations indicated that the olfactory recognition memory performance can be predicted in man from odour-elicited semantic profiles by using artificial neural networks. It was also shown that all semantic descriptors do not participate in olfactory recognition to the same degree. Low-level information, such as intensity, familiarity and hedonic judgements, did not allow the artificial neural network to predict the olfactory performance. By contrast, high-level information, such as gustatory, olfactory and visual evocations, allowed artificial networks to make such predictions.