Alliesthesia to food cues: Heterogeneity across stimuli and sensory modalities

Guidelines for assessment of affect-related constructs

Research on affect-related constructs as determinants of health behavior is increasing. The Affect and Health Behavior Framework (AHBF) provides a schematic structure to label, organize, and integrate affect-related constructs. To further facilitate research and theory development in health behavior science, the purpose of the present paper is to provide a critical review and guidelines for assessment of the affect-related constructs in the AHBF. The paper is organized based on the categories of constructs in the AHBF: Affective response to health behavior, incidental affect, affect processing, and affectively charged motivation. Future research should work toward parsing constructs where possible as well as identifying overlap. Researchers are advised to consider conceptual underpinnings and methodological nuances when assessing affect-related constructs in order to build a cumulative science of affective determinants of health behavior.

Episodic memory and recognition are influenced by cues' sensory modality: comparing odours, music and faces using virtual reality

Most everyday experiences are multisensory, and all senses can trigger the conscious re-experience of unique personal events embedded in their specific spatio-temporal context. Yet, little is known about how a cue's sensory modality influences episodic memory, and which step of this process is impacted. This study investigated recognition and episodic memory across olfactory, auditory and visual sensory modalities in a laboratory-ecological task using a non-immersive virtual reality device. At encoding, participants freely and actively explored unique and rich episodes in a three-room house where boxes delivered odours, musical pieces and pictures of face. At retrieval, participants were presented with modality-specific memory cues and were told to 1) recognise encoded cues among distractors and, 2) go to the room and select the box in which they encountered them at encoding. Memory performance and response times revealed that music and faces outperformed odours in recognition memory, but that odours and faces outperformed music in evoking encoding context. Interestingly, correct recognition of music and faces was accompanied by more profound inspirations than correct rejection. By directly comparing memory performance across sensory modalities, our study demonstrated that despite limited recognition, odours are powerful cues to evoke specific episodic memory retrieval.

Odor Hedonic Profile (OHP): a self-rating tool of everyday odors

Odor hedonic estimation (pleasant/unpleasant) is considered the first and one of the most important dimensions in odor perception. Although there are several published scales that rate odor hedonicity, most of them use odorants that induce biases related to stimulus properties or test conditions and make difficult clinical or industrial applications. Thus, this study aimed to propose a model of odor hedonic profile (OHP) based on 14 items related to everyday odors without stimulus. The OHP is a self-rating tool based on the hedonic estimate representation and allows the determination of specific profiles, i.e., "conservative," "neutral," "liberal," "negative olfactory alliesthesia," and "positive olfactory alliesthesia." It can be useful in different contexts (e.g., food studies) and general pathologies (e.g., eating disorders) or pathologies with mood/emotional disturbances (e.g., depression).

Predictors of state-based changes in wanting and liking

People report wanting food when they are hungry, and on eating it they typically report liking the experience. After eating, both wanting and liking decline, but wanting declines to a greater extent, which we term the 'affective discrepancy effect'. In this study we examine the predictors - state, sensory and memory-based - of these affective changes. Hungry participants undertook three tasks: (1) written recollections of what certain foods are like to eat; (2) ratings of wanting and expected flavour liking and fillingness when looking at snacks, and ratings of food and flavour liking when eating them; (3) ratings of bodily state. These tasks were then repeated after lunch. State-based changes in food liking were best predicted by changes in flavour liking. For state-based change in wanting, memory-based information about flavour liking and fillingness from tasks (1) and (2) were all significant predictors. For recollections about eating (task 1), mentions of food fillingness significantly increased pre-to post-lunch and this was the best predictor of the affective discrepancy effect. Recollections of food fillingness are state-dependent, and can arise unbidden (i.e., such recollective content was unprompted). This may reflect one way that memory may selectively influence wanting, and hence whether food intake is initiated or not.

The nose is hungrier than the eyes

Vision and olfaction are the main sensory channels for appraising food prior to eating. Motivational models often assume that these sensory channels function in an equivalent manner. We tested this notion by asking participants to rate their desire for some snacks only via smell and others only via vision. In the next phase, participants consumed a small sample of every snack, now with all of the senses available, rating liking and desire for more. After consuming a meal, participants repeated the desire/liking test. Sensing via olfaction, relative to vision, led to greater desire ratings irrespective of state. When hungry, judgments of liking and desire for more were higher for foods that were initially smelled relative to those that were initially seen. Across the meal, visually based desire ratings declined more than those based on smell, relative to ratings made when the snacks were tasted. Together, this suggests motivational equivalence does not hold for olfaction and vision. We suggest this may be due to a greater reliance on memory for generating visually based desire.

Assessment of odor hedonic perception: the Sniffin' sticks parosmia test (SSParoT)

Qualitative olfactory dysfunction is characterized as distorted odor perception and can have a profound effect on quality of life of affected individuals. Parosmia and phantosmia represent the two main subgroups of qualitative impairment and are currently diagnosed based on patient history only. We have developed a test method which measures qualitative olfactory function based on the odors of the Sniffin' Sticks Identification subtest. The newly developed test is called Sniffin' Sticks Parosmia Test (SSParoT). SSParoT uses hedonic estimates of two oppositely valenced odors (pleasant and unpleasant) to assess hedonic range (HR) and hedonic direction (HD), which represent qualitative olfactory perception. HR is defined as the perceivable hedonic distance between two oppositely valenced odors, while HD serves as an indicator for overall hedonic perception of odors. This multicenter study enrolled a total of 162 normosmic subjects in four consecutive experiments. Cluster analysis was used to group odors from the 16-item Sniffin' Sticks Identification test and 24-additional odors into clusters with distinct hedonic properties. Eleven odor pairs were found to be suitable for estimation of HR and HD. Analysis showed agreement between test-retest sessions for all odor pairs. SSparoT might emerge as a valuable tool to assess qualitative olfactory function in health and disease.

Incorporation of fragmented visuo-olfactory episodic memory into dreams and its association with memory performance

The question of a possible link between dream content and memory consolidation remains open. After a comprehensive review of the literature, we present novel findings from an experiment testing whether the incorporation of recently learned stimuli into dream reports is associated with improved post-sleep memory performance. Thirty-two high dream recallers freely explored new visuo-olfactory episodes for 3 consecutive days. During the nights following each non-explicit encoding, participants wore a wrist actimeter, and woke up at 5am and their usual waking time to record their dreams (intensity of all oneiric sensory perception was assessed using scales). A total of 120 dreams were reported and elements related to the encoding phase were identified in 37 of them, either learning-related (mainly visual- and rarely olfactory-related elements), or experiment-related (lab- or experimenters-related elements). On the 4^th day, we found that participants with learning-related (n = 16) and participants with learning-related and/or experiment-related dreams (n = 21) had similar odor recognition and odor-evoked episodic memory with the other participants. However, they had significantly better visuo-spatial memory of the episodes in comparison to the other participants. Our results support the hypothesis that the learning phase is loosely incorporated into dreams and that this incorporation is associated with sleep related memory consolidation.

Amygdala activation during unconscious visual processing of food

Hedonic or emotional responses to food have important positive and negative effects on human life. Behavioral studies have shown that hedonic responses to food images are elicited rapidly, even in the absence of conscious awareness of food. Although a number of previous neuroimaging studies investigated neural activity during conscious processing of food images, the neural mechanisms underlying unconscious food processing remain unknown. To investigate this issue, we measured neural activity using functional magnetic resonance imaging while participants viewed food and mosaic images presented subliminally and supraliminally. Conjunction analyses revealed that the bilateral amygdala was more strongly activated in response to food images than to mosaic images under both subliminal and supraliminal conditions. Interaction analyses revealed that the broad bilateral posterior regions, peaking at the posterior fusiform gyrus, were particularly active when participants viewed food versus mosaic images under the supraliminal compared with the subliminal condition. Dynamic causal modeling analyses supported the model in which the subcortical visual pathway from the pulvinar to the amygdala was modulated by food under the subliminal condition; in contrast, the model in which both subcortical and cortical (connecting the primary visual cortex, fusiform gyrus, and the amygdala) visual pathways were modulated by food received the most support under the supraliminal condition. These results suggest the possibility that unconscious hedonic responses to food may exert an effect through amygdala activation via the subcortical visual pathway.

Dysfunction of the to in Anorexia and Bulimia Nervosa: A fMRI

Brain reward dysfunction in eating disorders has been widely reported. However, whether the neural correlates of hedonic and motivational experiences related to food cues are differentially affected in anorexia nervosa of restrictive type (ANr), bulimia nervosa (BN), and healthy control (HC) participants remains unknown. Here, 39 women (14 ANr, 13 BN, and 12 HC) underwent fMRI while smelling food or non-food odors in hunger and satiety states during liking and wanting tasks. ANr and BN patients reported less desire to eat odor-cued food and odor-cued high energy-density food (EDF), respectively. ANr patients exhibited lower ventral tegmental area (VTA) activation than BN patients to food odors when rating their desire to eat, suggesting altered incentive salience attribution to food odors. Compared with HC participants, BN patients exhibited decreased activation of the caudate nucleus to food odors in the hunger state during the wanting task. Both patient groups also showed reduced activation of the anterior ventral pallidum and insula in response to high EDF odors in the hunger state during the wanting task. These findings indicate that brain activation within the food reward-regulating circuit differentiates the three groups. ANr patients further exhibited lower activation of the precuneus than other participants, suggesting a possible role of body image distortion in ANr. Our study highlights that food odors are relevant sensory probes to gain better insight into the dysfunction of the mesolimbic and striatal circuitry involved in food reward processing in patients with EDs.

Homeostatic modulation on unconscious hedonic responses to food

OBJECTIVE

Hedonic/affective responses to food play a critical role in eating behavior. Previous behavioral studies have shown that hedonic responses to food are elicited consciously and unconsciously. Although the studies also showed that hunger and satiation have a modulatory effect on conscious hedonic responses to food, the effect of these homeostatic states on unconscious hedonic responses to food remains unknown.

RESULTS

We investigated unconscious hedonic responses to food in hungry and satiated participants using the subliminal affective priming paradigm. Food images or corresponding mosaic images were presented in the left or right peripheral visual field during 33 ms. Then photographs of target faces with emotionally neutral expressions were presented, and the participants evaluated their preference for the faces. Additionally, daily eating behaviors were assessed using questionnaires. Preference for the target faces was increased by food images relative to the mosaics in the hungry, but not the satiated, state. The difference in preference ratings between the food and mosaic conditions was positively correlated with the tendency for external eating in the hungry, but not the satiated, group. Our findings suggest that homeostatic states modulate unconscious hedonic responses to food and that this phenomenon is related to daily eating behaviors.

Benefits of a hungry mind: When hungry, exposure to food facilitates proactive interference resolution

Hunger is an everyday motivational state, which biases cognition to detect food. Although evidence exists on how hunger affects basic attentional and mnemonic processes, less is known about how motivational drive for food modulates higher cognition. We aimed to investigate the effects of food deprivation on proactive interference resolution, in the presence and absence of food. Normal-weight participants performed a recency probes paradigm providing an experimental block with food and object stimuli as well as a control block with object stimuli only, in a fasted and a sated state. Results showed that the interaction of shifts in nutritional state with the perception of food cues evoked an altered resolution of proactive interference. Satiety led to impaired performance, whereas a hungry state resulted in strengthened resistance to proactive interference and lying in between, the control block presenting neutral objects remained unaffected by nutritional state manipulation. Additionally, a further increase in proactive interference resolution occurred when the conflicting probe depicted food compared to non-food objects. We conclude that when exposed to food, hunger initiates biased competition of active memory representations in favor of prioritized source information at cost of familiar, but irrelevant information. The implications of these findings are discussed in terms of an arousal-biased competition in working memory.

The Neural Bases of Disgust for Cheese: An fMRI Study

The study of food aversion in humans by the induction of illness is ethically unthinkable, and it is difficult to propose a type of food that is disgusting for everybody. However, although cheese is considered edible by most people, it can also be perceived as particularly disgusting to some individuals. As such, the perception of cheese constitutes a good model to study the cerebral processes of food disgust and aversion. In this study, we show that a higher percentage of people are disgusted by cheese than by other types of food. Functional magnetic resonance imaging then reveals that the internal and external globus pallidus and the substantia nigra belonging to the basal ganglia are more activated in participants who dislike or diswant to eat cheese (Anti) than in other participants who like to eat cheese, as revealed following stimulation with cheese odors and pictures. We suggest that the aforementioned basal ganglia structures commonly involved in reward are also involved in the aversive motivated behaviors. Our results further show that the ventral pallidum, a core structure of the reward circuit, is deactivated in Anti subjects stimulated by cheese in the wanting task, highlighting the suppression of motivation-related activation in subjects disgusted by cheese.

Prandial States Modify the Reactivity of the Gustatory Cortex Using Gustatory Evoked Potentials in Humans

Previous functional Magnetic Resonance Imaging studies evaluated the role of satiety on cortical taste area activity and highlighted decreased activation in the orbito-frontal cortex when food was eaten until satiation. The modulation of orbito-frontal neurons (secondary taste area) by ad libitum food intake has been associated with the pleasantness of the food's flavor. The insula and frontal operculum (primary taste area) are also involved in reward processing. The aim was to compare human gustatory evoked potentials (GEP) recorded in the primary and secondary gustatory cortices in a fasted state with those after food intake. Fifteen healthy volunteers were enrolled in this observational study. In each of two sessions, two GEP recordings were performed (at 11:00 am and 1:30 pm) in response to sucrose gustatory stimulation, and a sucrose-gustatory threshold was determined. During one session, a standard lunch was provided between the two GEP recordings. During the other session, subjects had nothing to eat. Hunger sensation, wanting, liking, and the perception of the solution's intensity were evaluated with visual analog scales. GEP latencies measured in the Pz (p < 0.001), Cz (p < 0.01), Fz (p < 0.001) recordings (primary taste area) were longer after lunch than in the pre-prandial condition. Fp1 and Fp2 latencies (secondary taste area) tended to be longer after lunch, but the difference was not significant. No difference was observed for the sucrose-gustatory threshold regardless of the session and time. Modifications in the primary taste area activity during the post-prandial period occurred regardless of the nature of the food eaten and could represent the activity of the frontal operculum and insula, which was recently shown to be modulated by gut signals (GLP-1, CCK, ghrelin, or insulin) through vagal afferent neurons or metabolic changes of the internal milieu after nutrient absorption. This trial was registered at clinicalstrials.gov as NCT02472444.

"What-Where-Which" Episodic Retrieval Requires Conscious Recollection and Is Promoted by Semantic Knowledge

Episodic memory is defined as the conscious retrieval of specific past events. Whether accurate episodic retrieval requires a recollective experience or if a feeling of knowing is sufficient remains unresolved. We recently devised an ecological approach to investigate the controlled cued-retrieval of episodes composed of unnamable odors (What) located spatially (Where) within a visual context (Which context). By combining the Remember/Know procedure with our laboratory-ecological approach in an original way, the present study demonstrated that the accurate odor-evoked retrieval of complex and multimodal episodes overwhelmingly required conscious recollection. A feeling of knowing, even when associated with a high level of confidence, was not sufficient to generate accurate episodic retrieval. Interestingly, we demonstrated that the recollection of accurate episodic memories was promoted by odor retrieval-cue familiarity and describability. In conclusion, our study suggested that semantic knowledge about retrieval-cues increased the recollection which is the state of awareness required for the accurate retrieval of complex episodic memories.

Metabolic and Sensory Influences on Odor Sensitivity in Humans

Our olfactory sense plays an important role in eating behavior by modulating our food preferences and intake. However, hunger or satiety may also influence how we perceive odors. Albeit speculative, contradictory results found in the past may have resulted from confounding by type of meal that participants ate to induce satiety. We aimed to investigate the influence of hunger state on olfactory sensitivity, comparing hunger to satiety using 2 different types of lunch to control for sensory-specific satiety. Odor detection thresholds were measured in 2 groups of participants (39 per group, 18-40 years), under 3 conditions: when hungry (twice), after a sweet lunch, and after a savory lunch. One group had their detection thresholds tested for a sweet odor, whereas in the other group, sensitivity to a savory odor was measured. Differences in olfactory sensitivity conditions were analyzed using linear mixed models. Participants had higher scores on the odor sensitivity task in a hungry versus satiated state (P = 0.001). Within the satiated condition, there was no effect of type of lunch on odor sensitivity. In conclusion, hunger slightly enhances sensitivity to food odors, but did not significantly depend on the type of food participants ate, suggesting no clear influence of sensory-specific satiety.

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.

A unique memory process modulated by emotion underpins successful odor recognition and episodic retrieval in humans

We behaviorally explore the link between olfaction, emotion and memory by testing the hypothesis that the emotion carried by odors facilitates the memory of specific unique events. To investigate this idea, we used a novel behavioral approach inspired by a paradigm developed by our team to study episodic memory in a controlled and as ecological as possible way in humans. The participants freely explored three unique and rich laboratory episodes; each episode consisted of three unfamiliar odors (What) positioned at three specific locations (Where) within a visual context (Which context). During the retrieval test, which occurred 24–72 h after the encoding, odors were used to trigger the retrieval of the complex episodes. The participants were proficient in recognizing the target odors among distractors and retrieving the visuospatial context in which they were encountered. The episodic nature of the task generated high and stable memory performances, which were accompanied by faster responses and slower and deeper breathing. Successful odor recognition and episodic memory were not related to differences in odor investigation at encoding. However, memory performances were influenced by the emotional content of the odors, regardless of odor valence, with both pleasant and unpleasant odors generating higher recognition and episodic retrieval than neutral odors. Finally, the present study also suggested that when the binding between the odors and the spatio-contextual features of the episode was successful, the odor recognition and the episodic retrieval collapsed into a unique memory process that began as soon as the participants smelled the odors.

Colour, pleasantness, and consumption behaviour within a meal

It is often claimed that colour (e.g., in a meal) affects consumption behaviour. However, just how strong is the evidence in support of this claim, and what are the underlying mechanisms? It has been shown that not only the colour itself, but also the variety and the arrangement of the differently-coloured components in a meal influence consumers' ratings of the pleasantness of a meal (across time) and, to a certain extent, might even affect their consumption behaviour as well. Typically, eating the same food constantly or repeatedly leads to a decrease in its perceived pleasantness, which, as a consequence, might lead to decreased intake of that food. However, variation within a meal (in one or several sensory attributes, or holistically) has been shown to slow down this process. In this review, we first briefly summarize the literature on how general variety in a meal influences these variables and the major theories that have been put forward by researchers to explain them. We then go on to evaluate the evidence of these effects based mainly on the colour of the food explaining the different processes that might affect colour-based sensory-specific satiety and, in more detail, consumption behaviour. In addition, we also discuss the overlap in the definitions of these terms and provide additional hypothesis as to why, in some cases, the opposite pattern of results has been observed.

Fasting for 24 hours heightens reward from food and food-related cues

Introduction

We examined the impact of a 24 hour complete fast (vs. fed state) on two measures of food reward: 1) ‘wanting’, as measured by response to food images and by the relative-reinforcing value of food (RRV), and 2) ‘liking’, as measured by response to food images and the hedonic evaluation of foods consumed.

Methods

Utilizing a randomized crossover design, 15 subjects (9 male; 6 female) aged 28.6±4.5 yrs with body mass index 25.3±1.4 kg/m² were randomized and counterbalanced to normal feeding (FED) and 24-hour fast (FASTED) conditions. Trait characteristics were measured with the Three Factor Eating Questionnaire. Two computer tasks measured food reward: 1) RRV progressive ratio task, 2) explicit ‘liking’ and ‘wanting’ (Leeds Food Preference Questionnaire, LFPQ). Also measured were ad libitum energy intake (EI; buffet) and food ‘liking’ (visual analogue scale) of personalized stimuli.

Results

There were no significant anthropometric changes between conditions. Appetite scores, hedonic ratings of ‘liking’, and ad libitum EI all significantly increased under the FASTED condition (p<0.05). Under the FASTED condition there were significant increases in the RRV of snack foods; similarly, explicit ‘wanting’ and ‘liking’ significantly increased for all food categories. ‘Liking’ of sweet foods remained high across-meals under FASTED, but savory foods decreased in hedonic saliency.

Conclusion

Relative to a fed state, we observed an increase in hedonic ratings of food, the rewarding value of food, and food intake after a 24 hr fast. Alliesthesia to food and food cues is suggested by heightened hedonic ratings under the FASTED condition relative to FED.

Children's reward responses to picture- and odor-cued food stimuli: a developmental analysis between 6 and 11years

The reward system is largely involved in the control of food intake. Whether components of this system (i.e., wanting and liking) change during development remains understudied, as well as how proximate factors (sensory cues, motivational state) modulate reward reactivity across development. We examined the developmental pattern of wanting and liking for sensorily-cued food stimuli in 6-11year old children as a function of the child's motivational state (hunger/satiety), gender, and the nature of foods. School children were exposed before or after their lunch on alternative days to visual and odor stimuli representing different categories of familiar foods. Their task was to rate wanting and liking of pictures and odorants of pizza, meat, vegetables, fruits, and chocolate. The following results were found: (1) While liking appeared to be stable from age 6 to 11, more particularly for visually-cued foods, wanting decreased, as well as did subjective hunger perception; (2) there were smaller or absent state-effects in 7-to-9-year-olds; (3) reward ratings were higher in boys than in girls; (4) reward ratings of vegetables were the lowest at all ages. These results suggest that wanting, but not liking, is developmentally variable over childhood, and that this variation depends on age, gender, motivational state (hunger/satiety), the nature of the food and the modality of the sensory cue representing it. Such developmental changes are discussed in relation to biological (adiposity rebound) and cognitive (dietary restraint) factors influencing the motivation to eat during middle (6-7years) and late (9-11years) childhood.

A novel experimental approach to episodic memory in humans based on the privileged access of odors to memories

Episodic memory is defined as the conscious recollection of a personal event (What) in its spatial (Where) and contextual (Which context) environment. In existing approaches, human episodic memory is either explored separately from real-life situations or is not fully controlled. In this study, we propose an intermediate approach, inspired by animal studies, that permits the control of the encoding and recall phases, while still being ecologically valid. As odors are known to be especially evocative reminders, we explored the memory of olfactory episodes. During trial-unique encoding, participants freely explored three episodes, one episode per day, each composed of three unnamable odors (What) that were positioned at specific locations on a board (Where) within a visual context (Which context). On the fourth day, both old and new odors were presented, and when an odor was recognized, the participants had to remember both its spatial location and the visual context in which it occurred. In Experiment 1, the participants were highly proficient at recognizing odors, and they recall the spatio-contextual environment associated with these odors in approximately half of the trials. To adapt the recall procedure to the constraints of fMRI, we conducted Experiment 2 demonstrating that trial repetition did not disturb the memory process. Thus, we first validated our protocol, which investigates the memory of olfactory episodes in a fully controlled way that is as close as possible to real-life situations. Then, we demonstrated the adaptability of our protocol for the future exploration of the neural networks implicated in episodic recall.

Olfaction under metabolic influences

Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin. In view of the worldwide health concern regarding the rising incidence of diabetes, obesity, and related metabolic disorders, we present a comprehensive review that addresses the current knowledge of hormonal modulation of olfactory perception and how disruption of hormonal signaling in the olfactory system can affect energy homeostasis.

Chronic restricted access to food leading to undernutrition affects rat neuroendocrine status and olfactory-driven behaviors

Previous studies have demonstrated that olfactory-driven behaviors in rats are influenced by short-term caloric restriction, partly through the modulation of olfactory sensitivity by appetite-modulating hormones or peptides such as insulin and leptin. Here, we addressed the issue of a long-term modulation of their neuroendocrine status by evaluating the effect of chronic food restriction in rats following a limitation of the duration of daily food intake to 2 h (SF) instead of 8 h (LF) on the expression of insulin and leptin system in the olfactory mucosa and bulb and on olfactory behaviors. This restriction resulted in a one-third reduction in the daily food intake and a 25% reduction in the body weight of SF rats when compared to controls, and was accompanied by lower levels of triglycerides, glucose, insulin and leptin in SF rats. Under these conditions, we observed a modulation of olfactory-mediated behaviors regarding food odors. In addition, restriction had a differential effect on the expression of insulin receptors, but not that of leptin receptors, in the olfactory mucosa, whereas no transcriptional change was observed at the upper level of the olfactory bulb. Overall, these data demonstrated that long-term changes in nutritional status modulate olfactory-mediated behaviors. Modulation of insulin system expression in the olfactory mucosa of food restricted rats suggests that this hormone could be part of this process.

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 6-11 years 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.

Sucrose self-administration and CNS activation in the rat

We have previously reported that administration of insulin into the arcuate nucleus of the hypothalamus decreases motivation for sucrose, assessed by a self-administration task, in rats. Because the pattern of central nervous system (CNS) activation in association with sucrose self-administration has not been evaluated, in the present study, we measured expression of c-Fos as an index of neuronal activation. We trained rats to bar-press for sucrose, according to a fixed-ratio (FR) or progressive-ratio (PR) schedule and mapped expression of c-Fos immunoreactivity in the CNS, compared with c-Fos expression in handled controls. We observed a unique expression of c-Fos in the medial hypothalamus (the arcuate, paraventricular, retrochiasmatic, dorsomedial, and ventromedial nuclei) in association with the onset of PR performance, and expression of c-Fos in the lateral hypothalamus and the bed nucleus of stria terminalis in association with the onset of FR performance. c-Fos expression was increased in the nucleus accumbens of both FR and PR rats. Our study emphasizes the importance of both hypothalamic energy homeostasis circuitry and limbic circuitry in the performance of a food reward task. Given the role of the medial hypothalamus in regulation of energy balance, our study suggests that this circuitry may contribute to reward regulation within the larger context of energy homeostasis.

Hedonic reactivity to visual and olfactory cues: rapid facial electromyographic reactions are altered in anorexia nervosa

Though it has been suggested that hedonic processing is altered in anorexia nervosa (AN), few studies have used objective measures to assess affective processes in this eating disorder. Accordingly, we investigated facial electromyographic, autonomic and subjective reactivity to the smell and sight of food and non-food stimuli, and assessed more particularly rapid facial reactions reflecting automatic processing of pleasantness. AN and healthy control (HC) women were exposed, before and after a standardized lunch, to pictures and odorants of foods differing in energy density, as well as to non-food sensory cues. Whereas the temporal profile of zygomatic activity in AN patients was typified by a fast drop to sensory cues within the 1000 ms following stimulus onset, HC showed a larger EMG reactivity to pictures in a 800-1000 ms time window. In contrast, pleasantness ratings discriminated the two groups only for high energy density food cues suggesting a partial dissociation between objective and subjective measures of hedonic processes in AN patients. The findings suggest that the automatic processing of pleasantness might be altered in AN, with the sensitivity to reward being modulated by controlled processes.

Pleasure for visual and olfactory stimuli evoking energy-dense foods is decreased in anorexia nervosa

Although patients with anorexia nervosa have been suggested to be anhedonic, few experiments have directly measured their sensory pleasure for a range of food and non-food stimuli. This study aimed to examine whether restrictive anorexia nervosa (AN-R) patients displayed: i) a generalized decline in sensory pleasure or only in food-related sensory pleasure; ii) a modification of hedonic responses to food cues (liking) and of the desire to eat foods (wanting) as a function of their motivational state (hunger vs. satiety) and energy density of foods (high vs. low). Forty-six female participants (AN-R n=17; healthy controls (HC) n=29) reported before/after lunch their pleasure for pictures/odorants representing foods of different energy density and non-food objects. They also reported their desire to eat the foods evoked by the sensory stimuli, and completed the Physical Anhedonia Scale and the Beck Depression Inventory. AN-R and HC participants did not differ on liking ratings when exposed to low energy-density food or to non-food stimuli. The two groups also had similar physical anhedonia scores. However, compared to HC, AN-R reported lower liking ratings for high energy food pictures regardless of their motivational state. Olfactory pleasure was reduced only during the pre-prandial state in the AN-R group. The wanting ratings showed a distinct pattern since AN-R participants reported less desire to eat the foods representing both low and high energy densities, but the effect was restricted to the pre-prandial state. Taken together these results reflect more the influence of core symptoms in anorexia nervosa (fear of gaining weight) than an overall inability to experience pleasure.

Reinforcing effects of nicotine and non-nicotine components of cigarette smoke

RATIONALE

Nicotine and non-nicotine components of cigarette smoke contribute to its reinforcing effects; however, the specific role of each component in maintaining behavior has not yet been elucidated.

OBJECTIVES

To assess the reinforcing effects of nicotine and non-nicotine components of cigarette smoke by presenting a concurrent choice paradigm in which participants had access to intravenous (IV) nicotine infusions vs. saline (placebo) infusions and puffs from denicotinized ("denic") cigarettes vs. air (sham puffs). We also measured the effects on self-administration of prior satiation with each component.

METHODS

Sixteen smokers participated in seven sessions: 1) a baseline smoking assessment, used to tailor the nicotine dose per infusion; 2) two sessions for training discrimination of IV nicotine vs. saline infusions and denic smoke vs. sham puffs; and 3) four sessions assessing choice behavior after different satiation conditions.

RESULTS

Denic smoke was self-administered more than any other alternative, including IV nicotine. IV nicotine, however, was preferred over IV saline and sham puffs. Preference for denic smoke vs. IV nicotine was inversely correlated with subjective ratings of "comfort" associated with nicotine. Smoke satiation reduced the number of denic puffs taken during choice periods, while prior nicotine administration did not affect puffing behavior. Smoking withdrawal symptoms were alleviated both by nicotine administration and by denic smoke.

CONCLUSIONS

In established smokers, non-nicotine aspects of cigarette smoking have potent reinforcing effects. While current smoking cessation pharmacotherapies primarily address the nicotine component of cigarette addiction, future cessation strategies should also be designed to target non-nicotine factors.