Non-food Odors Research Articles

Food-Related Odors Activate Dopaminergic Brain Areas.

Food-associated cues of different sensory categories have often been shown to be a potent elicitor of cerebral activity in brain reward circuits. Smells influence and modify the hedonic qualities of eating experience, and in contrast to smells not associated with food, perception of food-associated odors may activate dopaminergic brain areas. In this study, we aimed to verify previous findings related to the rewarding value of food-associated odors by means of an fMRI design involving carefully preselected odors of edible and non-edible substances. We compared activations generated by three food and three non-food odorants matching in terms of intensity, pleasantness and trigeminal qualities. We observed that for our mixed sample of 30 hungry and satiated participants, food odors generated significantly higher activation in the anterior cingulate cortex (right and left), insula (right), and putamen (right) than non-food odors. Among hungry subjects, regardless of the odor type, we found significant activation in the ventral tegmental area in response to olfactory stimulation. As our stimuli were matched in terms of various perceptual qualities, this result suggests that edibility of an odor source indeed generates specific activation in dopaminergic brain areas.

Odorant Normative Data for Use in Olfactory Memory Experiments: Dimension Selection and Analysis of Individual Differences.

The present study reports normative ratings for 200 food and non-food odors. One hundred participants rated odors across measures of verbalisability, perceived descriptive ability, context availability, pleasantness, irritability, intensity, familiarity, frequency, age of acquisition, and complexity. Analysis of the agreement between raters revealed that four dimensions, those of familiarity, intensity, pleasantness, and irritability, have the strongest utility as normative data. The ratings for the remaining dimensions exhibited reduced discriminability across the odor set and should therefore be used with caution. Indeed, these dimensions showed a larger difference between individuals in the ratings of the odors. Familiarity was shown to be related to pleasantness, and a non-linear relationship between pleasantness and intensity was observed which reflects greater intensity for odors that elicit a strong hedonic response. The suitability of these data for use in future olfactory study is considered, and effective implementation of the data for controlling stimuli is discussed.

Food-Related Odors and the Reward Circuit: Functional MRI

Eating is one of our basic needs, and food can be extremely rewarding. Different aspects of food can elicit the brain’s reward system. In the present study we set out to investigate differences in brain activity evoked by pleasant food and non-food odors, with a particular focus on dopaminergic brain regions. We measured cerebral activity in 23 participants by means of magnetic resonance imaging, who were stimulated with three food odors (strawberry, orange, and mango) and three non-food odors (lily of the valley, jasmine, and lavender). We acquired functional images using a block stimulation design. Participants also evaluated pleasantness, intensity, and edibility of the odorants. Food odors elicited larger activations in the left postcentral gyrus, the left superior frontal gyrus, and in the midbrain. However, despite careful piloting, food odors were on average rated as significantly more intense than the flower odors. We therefore restricted the subsequent analysis to odors which were matched with regard to intensity and pleasantness. Thus, comparing strawberry and lavender odor yielded significant activations in the right cingulate, the midbrain, and the insula bilaterally. We further extracted the percentage of signal change from the global mean (beta) for all odorants in all subjects’ ventral tegmental area, which revealed stronger signal change when subjects smelled food odors compared to flower odors. These results indicate that food-related odors may activate dopaminergic pathways in the brain, possibly due to a conditioned association.

The apéritif effect: Alcohol's effects on the brain's response to food aromas in women.

ObjectiveConsuming alcohol prior to a meal (an apéritif) increases food consumption. This greater food consumption may result from increased activity in brain regions that mediate reward and regulate feeding behavior. Using functional magnetic resonance imaging, we evaluated the blood oxygenation level dependent (BOLD) response to the food aromas of either roast beef or Italian meat sauce following pharmacokinetically controlled intravenous infusion of alcohol.MethodsBOLD activation to food aromas in non-obese women (n=35) was evaluated once during intravenous infusion of 6% v/v EtOH, clamped at a steady-state breath alcohol concentration of 50 mg/dL, and once during infusion of saline using matching pump rates. Ad libitum intake of roast beef with noodles or Italian meat sauce with pasta following imaging was recorded.ResultsBOLD activation to food relative to non-food odors in the hypothalamic area was increased during alcohol pre-load when compared to saline. Food consumption was significantly greater, and levels of ghrelin were reduced, following alcohol.ConclusionsAn alcohol pre-load increased food consumption and potentiated differences between food and non-food BOLD responses in the region of the hypothalamus. The hypothalamus may mediate the interplay of alcohol and responses to food cues, thus playing a role in the apéritif phenomenon.

Source localization of event-related brain activity elicited by food and nonfood odors

Tastes and odors influence the perception of a meal. Especially food aromas can act as potent signals to modulate our eating behavior with strong dependency on the reward produced by food. In this investigation we aimed to study the electrophysiological response to food- and non-food-related odors in healthy volunteers. Analyses revealed specific scalp potential maps for the two conditions; in particular the source of the map in the “food” condition seemed to be associated with the processing of rewards; the specific map in the “non-food” condition reflects odor characteristics excluding the reward.

Reward for food odors: an fMRI study of liking and wanting as a function of metabolic state and BMI.

Brain reward systems mediate liking and wanting for food reward. Here, we explore the differential involvement of the following structures for these two components: the ventral and dorsal striatopallidal area, orbitofrontal cortex (OFC), anterior insula and anterior cingulate. Twelve healthy female participants were asked to rate pleasantness (liking of food and non-food odors) and the desire to eat (wanting of odor-evoked food) during event-related functional magnetic resonance imaging (fMRI). The subjective ratings and fMRI were performed in hunger and satiety states. Activations of regions of interest were compared as a function of task (liking vs wanting), odor category (food vs non-food) and metabolic state (hunger vs satiety). We found that the nucleus accumbens and ventral pallidum were differentially involved in liking or wanting during the hunger state, which suggests a reciprocal inhibitory influence between these structures. Neural activation of OFC subregions was correlated with either liking or wanting ratings, suggesting an OFC role in reward processing magnitude. Finally, during the hunger state, participants with a high body mass index exhibited less activation in neural structures underlying food reward processing. Our results suggest that food liking and wanting are two separable psychological constructs and may be functionally segregated within the cortico-striatopallidal circuit.

Now You Like Me, Now You Don't: Impact of Labels on Odor Perception

Past research has shown that odor perception can be affected by how we label odors. The aim of this study was to expand on previous work by investigating the impact of labels on edibility, pleasantness, and intensity ratings as well as on reaction times when detecting labeled odors. We tested 50 subjects. Five odorants were administered, each with a positive and a negative label. Participants had to detect odors as fast as possible and then rate their edibility, pleasantness, and intensity. Because of a lack of fit, only 4 of the initial 5 odorants were analyzed. All odorants presented with positive labels were rated as being more edible than when they were presented with negative labels. Specifically, the effect was also seen for the 2 nonfood odorants suggesting an unbiased effect. All odorants presented with positive labels were rated as being more pleasant than when they were presented with negative labels. Labels also modulated intensity ratings and reaction times for some odors. In summary, odor labels affect pleasantness ratings and edibility perception. Although labels appear to also influence intensity ratings and reaction times, this seems to be a more complex relationship that could be modulated by additional factors such as odor valence, label fit, and possibly the edibility attributed to an odor or a label.

Odors: appetizing or satiating? Development of appetite during odor exposure over time

Exposure to palatable food odors influences appetite responses, either promoting or inhibiting food intake. Possibly, food odors are appetizing after a short exposure (of circa 1-3 min), but become satiating over time (circa 10-20 min). To investigate the effect of odor exposure on general appetite and sensory-specific appetite (SSA) over time. In a cross-over study, 21 unrestrained women (age: 18-45 years; BMI: 18.5-25 kg m(-2)) were exposed for 20 min to eight different odor types: five food odors, two nonfood odors and no-odor. All odors were distributed in a test room at suprathreshold levels. General appetite, SSA and salivation were measured over time. All food odors significantly increased general appetite and SSA, compared with the no-odor condition. The nonfood odors decreased general appetite. All effects did not change over time during odor exposure. Savory odors increased the appetite for savory foods, but decreased appetite for sweet foods, and vice versa after exposure to sweet odors. Neither food odors nor nonfood odors affected salivation. Palatable food odors were appetizing during and after odor exposure and did not become satiating over a 20-min period. Food odors had a large impact on SSA and a small impact on general appetite. Moreover, exposure to food odors increased the appetite for congruent foods, but decreased the appetite for incongruent foods. It may be hypothesized that, once the body is prepared for intake of a certain food with a particular macronutrient composition, it is unfavorable to consume foods that are very different from the cued food.

Cisplatin chemotherapy induces odor perception changes in bronchial cancer patients

A study of olfactory function was performed in 15 bronchial cancer patients receiving cisplatin and 15 control subjects. Whereas odor detection and odor identification abilities were not influenced by the administration of cisplatin, a decrease in pleasantness was observed only for food odors, and not for non-food odors. Taken as a whole, these findings suggest that cisplatin therapy in bronchial cancer patients impairs the pleasure of perceived food odors, which may account for disturbances in food intake and quality of life in this population.

Lower state of hunger enhances food odour sensitivity in a large student sample

Recent work has indicated that both hunger state and BMI can predict differences in olfactory sensitivity to food and non-food odors. The research here aimed to extend this research using a larger sample and simplified measure of olfactory threshold. Participants (n = 94) attended one session where following baseline ratings of hunger, they completed threshold tests for a food and non-food odor. Results demonstrated that when controlling for differences in BMI, individuals in a low state of hunger had greater sensitivity to the food associated odour. Additionally, there was a tendency for increases in BMI to predict lower sensitivity to the non-food odour. These findings support and extend previous research by demonstrating in a large healthy sample where hunger state was not directly manipulated, that detection of food odours is still facilitated in low states of hunger.

Non-food odorants reduce chocolate cravings

The present study compared the relative effectiveness of simple, commercially available food and non-food olfactory tasks on chocolate craving reduction. Chocolate cravings were induced by a series of coloured photographs and 67 undergraduate women were asked to smell one of three odours (green apple, jasmine, or water). The non-food odorant (jasmine) significantly reduced chocolate cravings relative to both the food and control odorants. Thus simple non-food odorants offer potential scope as a technique for curbing unwanted food cravings.

Correlation between Ventromedial Prefrontal Cortex Activation to Food Aromas and Cue-driven Eating: An fMRI Study.

Food aromas are signals associated with both food's availability and pleasure. Previous research from this laboratory has shown that food aromas under fasting conditions evoke robust activation of medial prefrontal brain regions thought to reflect reward value (Bragulat, et al. 2010). In the current study, eighteen women (eleven normal-weight and seven obese) underwent a two-day imaging study (one after being fed, one while fasting). All were imaged on a 3T Siemens Trio-Tim scanner while sniffing two food (F; pasta and beef) odors, one non-food (NF; Douglas fir) odor, and an odorless control (CO). Prior to imaging, participants rated hunger and perceived odor qualities, and completed the Dutch Eating Behavior Questionnaire (DEBQ) to assess "Externality" (the extent to which eating is driven by external food cues). Across all participants, both food and non-food odors (compared to CO) elicited large blood oxygenation level dependent (BOLD) responses in olfactory and reward-related areas, including the medial prefrontal and anterior cingulate cortex, bilateral orbitofrontal cortex, and bilateral piriform cortex, amygdala, and hippocampus. However, food odors produced greater activation of medial prefrontal cortex, left lateral orbitofrontal cortex and inferior insula than non-food odors. Moreover, there was a significant correlation between the [F > CO] BOLD response in ventromedial prefrontal cortex and "Externality" sub-scale scores of the DEBQ, but only under the fed condition; no such correlation was present with the [NF > CO] response. This suggests that in those with high Externality, ventromedial prefrontal cortex may inappropriately valuate external food cues in the absence of internal hunger.

Orofacial reactivity to the sight and smell of food stimuli. Evidence for anticipatory liking related to food reward cues in overweight children

Whether food liking may be a risk factor of overconsumption and overweight/obesity remains a controversial issue. So far, most studies used subjective reports to assess consummatory behavior, approaches that might overlook subtle or implicit hedonic changes to sensory properties of foods. Therefore, we used a cue-exposure approach by recording different measures of hedonic processes (orofacial reactivity, self-rated pleasantness, food preference) in 6–11years old overweight (n=20) and normal-weight (n=20) children. Children were exposed to the smell and sight of high and low-energy density food stimuli and to non-food stimuli during pre- and post-prandial states. Their facial and verbal responses were videotaped and parent’s reports of children’s eating styles and appetitive traits were collected using the Children’s Eating Behavior Questionnaire (CEBQ). Results showed that orofacial reactivity, as an objective measure of anticipatory liking, was more discriminative than self reports, with overweight children displaying more lip sucking than normal-weight children when exposed to high energy food pictures and to food odorants. Orofacial reactivity to food cues was also associated with BMI and children’s eating styles (food responsiveness, emotional overeating, and desire to drink). Finally, overweight children classified more frequently non-food odorants as members of the food category during the pre-prandial state than during the post-prandial state, suggesting a possible influence of affective/motivational bias on odor categorization. Our findings suggest that orofacial responsiveness may be relevant to assess the sensitivity to energy-dense food reward cues in overweight children and for signaling, as an index of anticipatory liking, a potential risk for the development of overweight/obesity.

Alliesthesia is greater for odors of fatty foods than of non-fat foods

Alliesthesia is the modulation of the rewarding value of a stimulus according to the internal state (hungry or satiated). This study aimed to evaluate this phenomenon as a function of the nature of the stimulus (odors evoking edible and non-edible items, and the food odors evoking fatty and non-fat foods) and to compare the effectiveness of two reward evaluations (measures of pleasantness and appetence) to reveal alliesthesia. The results showed that both fatty and non-fat food odors were judged as less pleasant and less appetent when the subjects were satiated than when they were hungry, whereas no such difference was observed for non-food odors. There was a greater decrease in appetence than there was in pleasantness. Moreover, the decrease in appetence was greater for fatty than for non-fat food odors, whereas the decrease in pleasantness was similar for both fatty and non-fat food odors. Our study allows for the definition of a more comprehensive pattern of alliesthesia based on odor category. It demonstrates that alliesthesia is specific to food odors and that it is more pronounced when odors are associated with fatty rather than non-fat foods. It also reveals that an appetence measure is more sensitive than a pleasantness measure for describing an acute reward modulation process.

Ghrelin Enhances Olfactory Sensitivity and Exploratory Sniffing in Rodents and Humans

Olfaction is an integral part of feeding providing predictive cues that anticipate ingestion. Although olfactory function is modulated by factors such as prolonged fasting, the underlying neural mechanisms remain poorly understood. We recently identified ghrelin receptors in olfactory circuits in the brain. We therefore investigated the role of the appetite-stimulating hormone ghrelin in olfactory processing in rodents and humans, testing the hypothesis that ghrelin lowers olfactory detection thresholds and enhances exploratory sniffing, both being related to food seeking. In rats, intracerebroventricular ghrelin decreased odor detection thresholds and increased sniffing frequency. In humans, systemic ghrelin infusions significantly enhanced sniff magnitudes in response to both food and nonfood odorants and air in comparison to control saline infusions but did not affect the pleasantness ratings of odors. This is consistent with a specific effect on odor detection and not the hedonic value of odors. Collectively, our findings indicate that ghrelin stimulates exploratory sniffing and increases olfactory sensitivity, presumably enhancing the ability to locate, identify, and select foods. This novel role is consistent with ghrelin's overall function as a signal amplifier at the molecular interface between environmental and nutritional cues and neuroendocrine circuits controlling energy homeostasis.

The insular taste cortex contributes to odor quality coding.

Despite distinct peripheral and central pathways, stimulation of both the olfactory and the gustatory systems may give rise to the sensation of sweetness. Whether there is a common central mechanism producing sweet quality sensations or two discrete mechanisms associated independently with gustatory and olfactory stimuli is currently unknown. Here we used fMRI to determine whether odor sweetness is represented in the piriform olfactory cortex, which is thought to code odor quality, or in the insular taste cortex, which is thought to code taste quality. Fifteen participants sampled two concentrations of a pure sweet taste (sucrose), two sweet food odors (chocolate and strawberry), and two sweet floral odors (lilac and rose). Replicating prior work we found that olfactory stimulation activated the piriform, orbitofrontal and insular cortices. Of these regions, only the insula also responded to sweet taste. More importantly, the magnitude of the response to the food odors, but not to the non-food odors, in this region of insula was positively correlated with odor sweetness rating. These findings demonstrate that insular taste cortex contributes to odor quality coding by representing the taste-like aspects of food odors. Since the effect was specific to the food odors, and only food odors are experienced with taste, we suggest this common central mechanism develops as a function of experiencing flavors.

Separate signals for orthonasal vs. retronasal perception of food but not nonfood odors.

There is a controversy concerning whether smelling via the nose (ortho-nasally) or the mouth (retro-nasally) represent two routes to the same modality or two distinct submodalities. Since olfactory coding is dependent upon experience, and since food odors are experienced retro-nasally, the authors tested the hypothesis that whether an odor represents a food may influence whether sensation via the two routes leads to separable responses. The authors demonstrate that salivary response to food odors decrease with repeated presentation and show that this response rebounds upon presentation of a novel food odor via the same route and upon presentation of the same food odor via a novel route. This finding indicates that the novel odor and the novel route represent distinct sensory signals. This effect is specific, in that it does not depend on differences in odor intensity or pleasantness and is selective, in that it occurs for food odors but not for equally pleasant and intense nonfood odors. These results demonstrate that separable signals are generated for the same food odor depending upon route and support the existence of category-specific processing.

PSYCHOLOGIC DIMENSIONS IN THE PERCEPTION OF EVERYDAY ODORS: PLEASANTNESS AND EDIBILITY

ABSTRACT Different studies have reported that when a wide range of odors are assessed at a similar odor intensity, the hedonic dimension (pleasantness) is the most salient. Multivariate statistical methods can be applied to odor profile databases in order to further understand other underlying dimensions in the psychologic perception of everyday smells. One of the few odor profile databases published in the literature using odorant samples representative of ordinary odors was obtained by Chrea and coworkers (2005) . In the present study, this data set was reanalyzed using principal component analysis. The first component was related with the hedonic dimension, while the second component discriminated food versus nonfood odors. These results suggest that ordinary smells could be classified according to their hedonic and edible character, which is of interest to provide some consensus in odor classification as well as to develop low‐dimensional odor maps. PRACTICAL APPLICATIONSDifferent classification schemes of ordinary odors have been proposed in the literature, but none of them is based on the psychologic dimensions of odor perception, which is the proposal of this study. In a reported research, a panel of about 120 subjects rated the hedonic tone of 146 odor descriptors on a numeric scale. Similarly, if a panel is asked to rate the hedonic as well as the edible character of a large set of odors, the results would allow the classification of odor descriptors according to both psychologic dimensions. A scatter plot of these ratings might be regarded as a two‐dimensional map of ordinary odors. The same idea could be extended to other relevant dimensions of olfactory perception space, which might provide the basis to develop low‐dimensional odor maps, as well as to achieve certain consensus in odor classification.

Ortho- and Retronasal Presentation of Olfactory Stimuli Modulates Odor Percepts

Retronasal olfaction gives us information important not only for the well-being by detecting dangerous substances but also provides a basis for the pleasures of eating and drinking. However, odors presented via the retronasal route appear to evoke different sensations compared to orthonasal presentation. In this study, we differentially stimulated anterior and posterior parts of the subjects’ nasal cavity with odors. Subjects were able to tell retronasal and orthonasal smelling apart; the ability of doing so seemed to be linked to but could not completely be explained by the degree to which the odorant stimulated the trigeminal nerve. Furthermore, we examined whether food and nonfood odors were perceived as differently pleasant, depending on the presentation site. In fact, some but not all nonfood odors were described as less pleasant when they were delivered retronasally. In conclusion, the present results clearly suggest that there are differences between sensations produced by presenting odors through the retronasal or the orthonasal route, which bears significance for both basic and applied research.

WITHDRAWN: It smells so good I can almost taste it: Evidence that food and nonfood odors are localized differently within the nasal cavity

The publisher regrets that this article is an accidental duplication of an article that has already been published, doi: 10.1016/j.appet.2006.03.001 . The duplicate article has therefore been withdrawn.