Food cue reactivity: Neurobiological and behavioral underpinnings

Impact of satiety on palatable food associative learning and consumption in male and female adult rats

Hedonic and memory mechanisms can stimulate food cravings and consumption in sated individuals, promoting binge eating and obesity. Despite that, how satiety impacts learning and memory about cues for palatable food in males and females remains unclear. This is the first study to directly compare food associative learning, extinction, and memory renewal between hungry and sated subjects of both sexes. Food-restricted and sated male and female adult Sprague Dawley rats were trained in Pavlovian cue-food conditioning sessions, followed by cue-only presentations during extinction in a different context. They were then tested for renewal of conditioned responding to the food cue by return to the conditioning context. Conditioned responding was assessed through foodcup approach behavior. These rats were also tested for consumption of palatable food and chow before and after the learning and memory protocol. Sated rats demonstrated learning, extinction, and renewal of conditioned responding, indicating that physiological hunger is not required for learning and memory of palatable food cues. There were differences during cue-food acquisition, food-deprived rats learned faster and reached a plateau in conditioned responding sooner than sated rats. However, there were no differences after the fourth session, when sated rats reached the same level of responding as the food-deprived rats. There were sex differences during early acquisition under sated but not hungry states. Sated females had higher conditioned responding than sated males, while food-deprived rats of both sexes responded similarly. Extinction and renewal tests showed that both hungry and sated rats successfully decreased and subsequently renewed their conditioned responses. These results demonstrate the durability of learning and persistence of food-cue memory regardless of hunger state. Consumption tests found that all rats prefer palatable food compared to chow. Females, particularly when sated, consumed more palatable food compared to males. Higher palatable food consumption and learning in females suggest an enhanced sensitivity to palatable rewards. Correlation analyses found a positive relation between the amounts of food rats consumed and their conditioned responding in both sexes. These results demonstrate robust associative learning and memory under satiety and add evidence of sex differences in hedonic food motivation.

Taming temptations: Comparing the effectiveness of counterconditioning and extinction in reducing food cue reactivity

In today's "obesogenic" environment, Pavlovian cues signaling the availability of high-calorie foods may elicit strong expectancies of eating and food cravings. Such cue-elicited appetitive responses, collectively referred to as food cue reactivity, may foster overeating and weight gain. Moreover, food-related cues may also elicit instrumental actions aimed at obtaining those foods via Pavlovian-to-Instrumental Transfer (PIT). This study compared extinction and counterconditioning in reducing food cue reactivity, measured by outcome expectancies, craving, and liking, as well as in decreasing outcome-specific PIT. We used a three-phase PIT paradigm: In the first two phases, participants learned Pavlovian associations between two conditioned stimuli (CSs+) and two food outcomes, and instrumental associations between two responses and the same outcomes. An additional stimulus was never paired with food outcomes (CS-). Participants then underwent either extinction or counterconditioning for one CS+ while the other CS+ remained unchanged, or received no additional learning (control). In the test phase, instrumental responding was measured in the presence and absence of Pavlovian stimuli. In all phases, we measured outcome expectancies, craving and liking of the Pavlovian stimuli. Both extinction and counterconditioning reduced cue-elicited outcome expectancies, but only counterconditioning significantly decreased CS+ liking. Neither procedure effectively reduced cue-elicited craving. Outcome-specific PIT was observed across conditions, though counterconditioning lead to a general decrease in instrumental responding to all stimuli in the test phase. These findings suggest that counterconditioning more effectively targets the affective value of conditioned stimuli and reduces food cue reactivity compared to extinction, though its impact on PIT warrants further investigation.

Best practices for including sex as a variable in appetite research

Despite increasing recognition that sex is a critical variable in appetite research, many studies fail to include participants of both sexes, fail to consider reproductive physiology in participant selection, or include both sexes but fail to test for sex differences in outcomes. To help remedy this situation, this article seeks to engender enthusiasm for including sex as a variable in appetite research. We first illustrate some sex differences in healthy and disordered eating, including both male-female differences and differences across the menstrual cycle. We next provide methodological guidance for studies involving male and female participants around puberty, during reproductive adulthood, and during reproductive senescence. Studies in children ≥5 y of age should consider adrenarche and gonadarche. Appetite studies in girls and women following menarche and similarly aged males should consider the influences of sex-specific aspects the hypothalamic-pituitary-gonadal (HPG) axis function. The cyclicity of HPG function (i.e., the menstrual cycle) in girls and women presents the challenge of identifying of menstrual-cycle subphases, which are highly variable within and between individuals. Reproductive senescence refers to changes in HPG axis function that occur in both men and women beginning in mid-life. Current best practices involve consideration of hormone-assay methodology, experimental design, and statistical analyses. On the horizon are options based on wearable-sensors and nanotechnology. Well informed consideration of sex as a variable will accelerate progress in appetite research by increasing rigor, replicability, and relevance.

Patterns of olfactory perception, eating behavior and body composition in adolescents with different body weights

PURPOSE

To evaluate associations between olfactory function, eating behavior, and characteristics of body composition in adolescents with different body weights.

METHODS

The study included 87 children aged 10-17 years with normal and excess body weight. The study group consisted of overweight and obese adolescents. All children underwent anthropometry with calculation of SDS body mass index (WHO Anthro Plus), body composition was assessed using Inbody 770, diagnosis of olfactory dysfunction was performed using a set of Sniffin Sticks (Odofin, Germany). The Dutch Eating Behavior Questionnaire was used for assessment of eating disorders. IBM SPSS. Statistics v.20 program was used for statistical analysis.

RESULTS

In adolescents with decreased sense of smell, regardless of SDS BMI, restrictive type of eating behavior was more common (p = 0.04). Among girls, hypoosmia was diagnosed in 21.7% (n = 10) of cases, being accompanied by a higher proportion of body fat, higher prevalence of emotionogenic type of eating behavior compared to girls without olfactory impairment, who, on the contrary, more frequently exhibited the restrictive type of eating disorder. Among boys, hypoosmia was found in 39% (n = 16) of cases. There were no statistically significant differences with the normoosmia subgroup in terms of eating behavior type and body composition parameters. Girls with hypoosmia showed positive associations between body fat percentage and discriminatory olfactory test results (r = 0.805; p = 0.020), externalizing type of eating behavior and BMI-FOR-AGE (r = 0.873; p = 0.005), body fat mass (r = 0.764; p = 0.027) and body fat percentage (r = 0.805; p = 0.016). The emotiogenic type of eating behavior showed significant correlations with total body phase angle (r = 0.805; p = 0.029), skeletal muscle mass (r = 0.791; p = 0.034). In boys with hypoosmia, positive associations were found between restrictive type of eating behavior and BMI-FOR-AGE (r = 0.784; p = 0.002), visceral fat area (r = 0.701; p = 0.008), body fat mass (r = 0.660; p = 0.014) and body fat percentage (r = 0.742; p = 0.004).

CONCLUSION

The results of this study suggest that hypoosmia is associated with changes in eating behavior and body composition in adolescents with different body weight, yet the direction of such casual relationship remains unclear.

Separate orexigenic hippocampal ensembles shape dietary choice by enhancing contextual memory and motivation

The hippocampus (HPC) has emerged as a critical player in the control of food intake, beyond its well-known role in memory. While previous studies have primarily associated the HPC with food intake inhibition, recent research suggests a role in appetitive processes. Here we identified spatially distinct neuronal populations within the dorsal HPC (dHPC) that respond to either fats or sugars, potent natural reinforcers that contribute to obesity development. Using activity-dependent genetic capture of nutrient-responsive dHPC neurons, we demonstrate a causal role of both populations in promoting nutrient-specific intake through different mechanisms. Sugar-responsive neurons encoded spatial memory for sugar location, whereas fat-responsive neurons selectively enhanced the preference and motivation for fat intake. Importantly, stimulation of either nutrient-responsive dHPC neurons increased food intake, while ablation differentially impacted obesogenic diet consumption and prevented diet-induced weight gain. Collectively, these findings uncover previously unknown orexigenic circuits underlying macronutrient-specific consumption and provide a foundation for developing potential obesity treatments.

Efficiency of post-meal memory inhibition predicts subsequent food intake

Memory processes may contribute to appetite regulation. When people look at palatable foods, their desire to consume them depends upon memory retrieval (i.e., recalling if it will taste good). If memory inhibition occurs during satiety, then pleasant eating-related memories will not be retrieved, making eating less likely. In contrast, if memory inhibition is less efficient, pleasant food-related memories will be retrieved, the food will appear desirable, and the chance of consumption increases. Here we tested whether a putative measure of memory inhibition could predict post-meal snack food intake. Study participants looked at palatable snacks and judged their desire to eat them (i.e., a memory-dependent process), and then ate a small sample of each food, and rated them for liking (i.e., an orosensory-dependent process) - all using category rating scales. Following a filling meal, this test was repeated, alongside others. Finally, participants were given the opportunity for ad libitum snack food consumption, in addition to collecting measures such as impulsivity. Poorer memory inhibition (i.e., smaller changes in wanting relative to liking from pre-to post-meal) was associated with greater consumption of snacks on the ad libitum test (Sr2% = 4.4, p = 0.006) after controlling for other variables likely to influence eating (e.g., impulsivity). This effect was maintained even when the memory inhibition measure was based on foods different to those being consumed on the ad libitum snacking test. In conclusion, memory inhibition may contribute to food intake regulation, and when this is less efficient, more palatable food is likely to be eaten in the post-meal period.

Pupillary dilation response to the auditory food words in adolescents with obesity without binge eating disorder

Childhood obesity is a growing global public health problem. Studies suggest that environmental cues contribute to developing and maintaining obesity. We aimed to evaluate pupillary changes to auditory food words vs. nonfood words and to conduct a dynamic temporal analysis of pupil size changes in adolescents with obesity without binge eating disorder by comparing healthy-weight adolescents. In this study, a total of 63 adolescents aged 12-18 years (n = 32, obesity group (OG); n = 31, control group (CG)) were included. In an auditory paradigm, participants were presented with a series of high and low-calorie food and nonfood words. A binocular remote eye-tracking device was used to measure pupil diameter. Generalized additive mixed models (GAMMs) were used for dynamic temporal analysis of pupillometry data. The results of GAMM analysis indicated that CG had larger pupil dilation than the OG while listening to auditory food words. CG had larger pupil dilation in food words than in nonfood words. However, the OG had a similar pupillary response in food and nonfood words. Pupil dilation response to higher-calorie foods was extended over the later stages of the time period (after 2000 ms) in the OG. In summary, our findings indicated that individuals with obesity had lower pupil dilation to auditory food words compared to normal-weight peers. Adolescents with obesity had prolonged pupillary dilation in higher calories of food words. The individual psychological factors affecting the dynamic changes of pupil responses to food cues in adolescents with obesity should be examined in further studies.

Category-specific general Pavlovian-instrumental transfer

Modern living is characterized by easy access to highly palatable energy-dense foods. Environmental cues associated with palatable foods increase seeking of those foods (specific transfer) and other palatable foods (general transfer). We conducted a series of studies testing the boundaries of food cue-reactivity by evaluating the impact of broader flavor associations (i.e. saltiness, sweetness) in eliciting general transfer effects. Experiment 1 was an online experiment with fictive rewards that tested if two actions associated with different food rewards (chip and chocolate points) could be provoked by images of other foods that were either similar or distinct in flavor from the foods associated with these instrumental actions. We observed that response excitation was only elicited by similarly flavored food cues, whereas distinctly flavored food cues inhibited response rates relative to control cues. Experiment 2 confirmed this observation in a classroom setting where real food rewards were contingent on task performance. Experiment 3 was an online study that further confirmed the reliability of the effects with a well powered sample. There were moderate-to-strong associations between specific and general transfer effects across all studies, suggesting overlapping cognitive processes are responsible for both transfer effects. These data improve the mechanistic understanding of how broad category associations can moderate the impact of food cues on food choices. This knowledge could be helpful for improving the precision of psychological interventions that seek to mitigate the impact of food cue-reactivity.

Cue-potentiated feeding in rodents: Implications for weight regulation in obesogenic environments

Cue-potentiated feeding (CPF) describes instances where food intake is increased by exposure to conditioned cues associated with food, often in the absence of hunger. CPF effects have been reported in a range of experimental protocols developed by researchers working across diverse fields spanning behavioural neuroscience, social psychology and ecology. Here we review the evolution of research on cue-potentiated feeding in animal models to identify important behavioural parameters and key neural circuits and pharmacological systems underlying the effect. Overall, evidence indicates that social, discrete and contextual stimuli can be used to elicit CPF effects across multiple species, though effects are often subtle and sensitive to procedural variables. While regular exposure to food cues is thought to be a key risk factor for overeating in so-called 'obesogenic' environments, further work is needed to identify whether CPF promotes positive energy balance and weight gain over the longer term. We suggest several methodological and conceptual areas for inquiry to elucidate the contribution of CPF to the regulation of food choice and energy intake.

Effects of Open-Label Placebos on Visual Food Cue Reactivity in Children and Adolescents

BACKGROUND

A high level of food cue reactivity (FCR) is a risk factor for overeating and weight gain. This randomized trial investigated whether open-label placebos (OLPs: placebos honestly administered) can reduce FCR (reported appetite) in children and adolescents.

METHOD

Children (n = 73; 8-12 years old) and adolescents (n = 187; 16-18 years old) were randomly assigned to either an OLP group or a control group (without OLP). Participants viewed images depicting food (sweets and fruits) and non-food items. Before viewing, the OLP group received a placebo for appetite reduction. Participants rated their desire to eat the depicted food items (0-100) and the perceived effectiveness of the OLP intervention.

RESULTS

The OLP exhibited a large effect in children, leading to a general reduction in appetite (group difference OLP vs. no OLP: M = -20.8; ηp2 = 0.20). This general effect was absent in adolescents, whose appetite reduction was restricted to fruits (OLP vs. no OLP: M = -8.1; ηp2 = 0.03). Additionally, children perceived the OLP as more effective than adolescents.

CONCLUSION

The reduced response and skeptical attitudes of adolescents towards OLP treatment require further investigation.

Hunger, Satiety, and Their Vulnerabilities

The psychological states of hunger and satiety play an important role in regulating human food intake. Several lines of evidence suggest that these states rely upon declarative learning and memory processes, which are based primarily in the medial temporal lobes (MTL). The MTL, and particularly the hippocampus, is unusual in that it is especially vulnerable to insult. Consequently, we examine here the impact on hunger and satiety of conditions that: (1) are central to ingestive behaviour and where there is evidence of MTL pathology (i.e., habitual consumption of a Western-style diet, obesity, and anorexia nervosa); and (2) where there is overwhelming evidence of MTL pathology, but where ingestive behaviour is not thought central (i.e., temporal lobe epilepsy and post-traumatic stress disorder). While for some of these conditions the evidence base is currently limited, the general conclusion is that MTL impairment is linked, sometimes strongly, to dysfunctional hunger and satiety. This focus on the MTL, and declarative learning and memory processes, has implications for the development of alternative treatment approaches for the regulation of appetite.

Obesity- and diet-induced plasticity in systems that control eating and energy balance

In April 2023, the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), in partnership with the National Institute of Child Health and Human Development, the National Institute on Aging, and the Office of Behavioral and Social Sciences Research, hosted a 2-day online workshop to discuss neural plasticity in energy homeostasis and obesity. The goal was to provide a broad view of current knowledge while identifying research questions and challenges regarding neural systems that control food intake and energy balance. This review includes highlights from the meeting and is intended both to introduce unfamiliar audiences with concepts central to energy homeostasis, feeding, and obesity and to highlight up-and-coming research in these areas that may be of special interest to those with a background in these fields. The overarching theme of this review addresses plasticity within the central and peripheral nervous systems that regulates and influences eating, emphasizing distinctions between healthy and disease states. This is by no means a comprehensive review because this is a broad and rapidly developing area. However, we have pointed out relevant reviews and primary articles throughout, as well as gaps in current understanding and opportunities for developments in the field.

Acute and chronic alcohol modulation of extended amygdala calcium dynamics

The central amygdala (CeA) and bed nucleus of the stria terminalis (BNST) are reciprocally connected nodes of the extended amygdala thought to play an important role in alcohol consumption. Studies of immediate-early genes indicate that BNST and CeA are acutely activated following alcohol drinking and may signal alcohol reward in nondependent drinkers, while stress signaling in the extended amygdala following chronic alcohol exposure drives increased drinking via negative reinforcement. However, the temporal dynamics of neuronal activation in these regions during drinking behavior are poorly understood. In this study, we used fiber photometry and the genetically encoded calcium sensor GCaMP6s to assess acute changes in neuronal activity during alcohol consumption in BNST and CeA before and after a chronic drinking paradigm. Activity was examined in the pan-neuronal population and separately in dynorphinergic neurons. BNST and CeA showed increased pan-neuronal activity during acute consumption of alcohol and other fluid tastants of positive and negative valence, as well as highly palatable chow. Responses were greatest during initial consummatory bouts and decreased in amplitude with repeated consumption of the same tastant, suggesting modulation by stimulus novelty. Dynorphin neurons showed similar consumption-associated calcium increases in both regions. Following three weeks of continuous alcohol access (CA), calcium increases in dynorphin neurons during drinking were maintained, but pan-neuronal activity and BNST-CeA coherence were altered in a sex-specific manner. These results indicate that BNST and CeA, and dynorphin neurons specifically, are engaged during drinking behavior, and activity dynamics are influenced by stimulus novelty and chronic alcohol.

The Cerebellar Response to Visual Portion Size Cues Is Associated with the Portion Size Effect in Children

The neural mechanisms underlying susceptibility to eating more in response to large portions (i.e., the portion size effect) remain unclear. Thus, the present study examined how neural responses to portion size relate to changes in weight and energy consumed as portions increase. Associations were examined across brain regions traditionally implicated in appetite control (i.e., an appetitive network) as well as the cerebellum, which has recently been implicated in appetite-related processes. Children without obesity (i.e., BMI-for-age-and-sex percentile < 90; N = 63; 55% female) viewed images of larger and smaller portions of food during fMRI and, in separate sessions, ate four meals that varied in portion size. Individual-level linear and quadratic associations between intake (kcal, grams) and portion size (i.e., portion size slopes) were estimated. The response to portion size in cerebellar lobules IV-VI was associated with the quadratic portion size slope estimated from gram intake; a greater response to images depicting smaller compared to larger portions was associated with steeper increases in intake with increasing portion sizes. Within the appetitive network, neural responses were not associated with portion size slopes. A decreased cerebellar response to larger amounts of food may increase children's susceptibility to overeating when excessively large portions are served.

Randomized Controlled Trial of Effects of Behavioral Weight Loss Treatment on Food Cue Reactivity

BACKGROUND

It is not known whether behavioral weight loss can attenuate blood oxygen level-dependent responses to food stimuli.

OBJECTIVES

This randomized controlled trial assessed the effects of a commercially available behavioral weight loss program (WW, WeightWatchers) compared to a wait-list control on blood oxygen level-dependent response to food cues.

METHODS

Females with obesity ( N = 61) were randomized to behavioral weight loss or wait-list control. At baseline and follow-up, participants completed assessments that included functional magnetic resonance imaging scans to assess response to images of high-calorie foods (HCF) or low-calorie foods (LCF), and neutral objects.

RESULTS

There were no significant between-group differences in change from baseline to follow-up in any regions of the brain in response to viewing HCF or LCF. From baseline to follow-up, participants in behavioral weight loss, compared with wait-list control, reported significantly greater increases in desire for LCF. Changes in liking and palatability of LCF and liking, palatability, and desire for HCF did not differ between groups.

DISCUSSION

Behavioral weight loss was associated with increased desire for LCF without changes in neural reactivity to food cues. These results suggest that alteration of neurological processes underlying responsiveness to food is difficult to achieve through behavioral weight management alone.

Short- and Long-Term High-Fat Diet Exposure Differentially Alters Phasic and Tonic GABAergic Signaling onto Lateral Orbitofrontal Pyramidal Neurons

The chronic consumption of caloric dense high-fat foods is a major contributor to increased body weight, obesity, and other chronic health conditions. The orbitofrontal cortex (OFC) is critical in guiding decisions about food intake and is altered with diet-induced obesity. Obese rodents have altered morphologic and synaptic electrophysiological properties in the lateral orbitofrontal cortex (lOFC). Yet the time course by which exposure to a high-fat diet (HFD) induces these changes is poorly understood. Here, male mice are exposed to either short-term (7 d) or long-term (90 d) HFD. Long-term HFD exposure increases body weight, and glucose signaling compared with short-term HFD or a standard control diet (SCD). Both short and long-term HFD exposure increased the excitability of lOFC pyramidal neurons. However, phasic and tonic GABAergic signaling was differentially altered depending on HFD exposure length, such that tonic GABAergic signaling was decreased with early exposure to the HFD and phasic signaling was changed with long-term diet exposure. Furthermore, alterations in the short-term diet exposure were transient, as removal of the diet restored electrophysiological characteristics similar to mice fed SCD, whereas long-term HFD electrophysiological changes were persistent and remained after HFD removal. Finally, we demonstrate that changes in reward devaluation occur early with diet exposure. Together, these results suggest that the duration of HFD exposure differentially alters lOFC function and provides mechanistic insights into the susceptibility of the OFC to impairments in outcome devaluation.SIGNIFICANCE STATEMENT This study provides mechanistic insight on the impact of short-term and long-term high-fat diet (HFD) exposure on GABAergic function in the lateral orbitofrontal cortex (lOFC), a region known to guide decision-making. We find short-term HFD exposure induces transient changes in firing and tonic GABA action on lOFC pyramidal neurons, whereas long-term HFD induces obesity and has lasting changes on firing, tonic GABA and inhibitory synaptic transmission onto lOFC neurons. Given that GABAergic signaling in the lOFC can influence decision-making around food, these results have important implications in present society as palatable energy dense foods are abundantly available.

Neural correlates of appetite in adolescents

Appetitive characteristics are associated with child adiposity, but their biological underpinnings are unclear. We sought to investigate the neural correlates of psychometric and behavioral measures of appetitive characteristics in youth. Adolescents (14-18y; 39F, 37M) varying in familial obesity risk and body weight (20% with overweight, 24% with obesity) viewed pictures of high energy-density (ED) foods, low-ED foods and non-foods during fMRI scanning on two separate days. On one day participants consumed a 474 ml preload of water (0 kcal, fasted) and on another (counter-balanced) 474 ml milkshake (480 kcal, fed), before scanning. A multi-item ad libitum meal (ALM) followed scanning. Parents completed Child Eating Behavior Questionnaire (CEBQ) sub-scales assessing food approach and food self-regulation. Caloric compensation was calculated as the percentage of preload intake compensated for by down-regulation of ALM intake in the fed vs. fasted condition. Analyses correcting for multiple comparisons demonstrated that, for the fasted condition, higher CEBQ Food Responsiveness scores were associated with greater activation to high-ED (vs. low-ED) foods in regions implicated in food reward (insula, rolandic operculum, putamen). In addition, higher caloric compensation was associated with greater fed vs. fasted activations in response to foods (vs. non-foods) in thalamus and supramarginal gyrus. Uncorrected analyses provided further support for associations of different measures of appetitive characteristics with brain responses to food cues in each condition. Measures of appetitive characteristics demonstrated overlapping and distinct associations with patterns of brain activation elicited by food cues in fasted and fed states. Understanding the neural basis of appetitive characteristics could aid development of biobehaviorally-informed obesity interventions.

CRH neurons in the lateral hypothalamic area regulate feeding behavior of mice

Food cues serve as pivotal triggers for eliciting physiological responses that subsequently influence food consumption. The magnitude of response induced by these cues stands as a critical determinant in the context of obesity risk. Nonetheless, the underlying neural mechanism that underpins how cues associated with edible food potentiate feeding behaviors remains uncertain. In this study, we revealed that corticotropin-releasing hormone (CRH)-expressing neurons in the lateral hypothalamic area played a crucial role in promoting consummatory behaviors in mice, shedding light on this intricate process. By employing an array of diverse assays, we initially established the activation of these neurons during feeding. Manipulations using optogenetic and chemogenetic assays revealed that their activation amplified appetite and promoted feeding behaviors, whereas inhibition decreased them. Additionally, our investigation identified downstream targets, including the ventral tegmental area, and underscored the pivotal involvement of the CRH neuropeptide itself in orchestrating this regulatory network. This research casts a clarifying light on the neural mechanism underlying the augmentation of appetite and the facilitation of feeding behaviors in response to food cues. VIDEO ABSTRACT.

What Is Food Noise? A Conceptual Model of Food Cue Reactivity

As GLP-1 receptor agonists, like semaglutide, emerge as effective treatments for weight management, anecdotal reports from patients and clinicians alike point to a reduction in what has been colloquially termed "food noise", as patients report experiencing less rumination and obsessive preoccupation about food. In this narrative review, we discuss concepts used in studies to investigate human eating behavior that can help elucidate and define food noise, particularly food cue reactivity. We propose a conceptual model that summarizes the main factors that have been shown to determine the magnitude of the reactivity elicited by external and internal food cues and how these factors can affect short- and long-term behavioral and clinical outcomes. By integrating key research conducted in this field, the Cue-Influencer-Reactivity-Outcome (CIRO) model of food cue reactivity provides a framework that can be used in future research to design studies and interpret findings related to food noise and food cue reactivity.

Separate orexigenic hippocampal ensembles shape dietary choice by enhancing contextual memory and motivation

The hippocampus (HPC), traditionally known for its role in learning and memory, has emerged as a controller of food intake. While prior studies primarily associated the HPC with food intake inhibition, recent research suggests a critical role in appetitive processes. We hypothesized that orexigenic HPC neurons differentially respond to fats and/or sugars, potent natural reinforcers that contribute to obesity development. Results uncover previously-unrecognized, spatially-distinct neuronal ensembles within the dorsal HPC (dHPC) that are responsive to separate nutrient signals originating from the gut. Using activity-dependent genetic capture of nutrient-responsive HPC neurons, we demonstrate a causal role of both populations in promoting nutrient-specific preference through different mechanisms. Sugar-responsive neurons encode an appetitive spatial memory engram for meal location, whereas fat-responsive neurons selectively enhance the preference and motivation for fat intake. Collectively, these findings uncover a neural basis for the exquisite specificity in processing macronutrient signals from a meal that shape dietary choices.

Discordance between assessments of food cue responsiveness: Implications for assessment in youth with overweight/obesity

Food cue responsiveness (FCR), broadly defined as behavioral, cognitive, emotional and/or physiological responses to external appetitive cues outside of physiological need, contributes to overeating and obesity among youth and adults. A variety of measures purportedly assess this construct, ranging from youth- or parent-report surveys to objective eating tasks. However, little research has assessed their convergence. It is especially important to evaluate this in children with overweight/obesity (OW/OB), as reliable and valid assessments of FCR are essential to better understand the role of this critical mechanism in behavioral interventions. The present study examined the relationship between five measures of FCR in a sample of 111 children with OW/OB (mean age = 10.6, mean BMI percentile = 96.4; 70% female; 68% white; 23% Latinx). Assessments included: objectively measured eating in the absence of hunger (EAH), parasympathetic activity when exposed to food, parent reported food responsiveness subscale from the Child Eating Behavior Questionnaire (CEBQ-FR), child self-reported Power of Food total score (C-PFS), and child self-reported Food Cravings Questionnaire total score (FCQ-T). Statistically significant spearman correlations were found between EAH and CEBQ-FR (ρ = 0.19, p < 0.05) and parasympathetic reactivity to food cues with both C-PFS (ρ = -0.32, p = 0.002) and FCQ-T (ρ = -0.34, p < 0.001). No other associations were statistically significant. These relationships remained significant in subsequent linear regression models controlling for child age and gender. The lack of concordance between measures assessing highly conceptually related constructs is of concern. Future studies should seek to elucidate a clear operationalization of FCR, examine the associations between FCR assessments in children and adolescents with a range of weight statuses, and evaluate how to best revise these measures to accurately reflect the latent construct being assessed.

The Effects of Food Advertisements on Food Intake and Neural Activity: A Systematic Review and Meta-Analysis of Recent Experimental Studies

Food advertisements are ubiquitous in our daily environment. However, the relationships between exposure to food advertising and outcomes related to ingestive behavior require further investigation. The objective was to conduct a systematic review and meta-analysis of behavioral and neural responses to food advertising in experimental studies. PubMed, Web of Science, and Scopus were searched for articles published from January 2014 to November 2021 using a search strategy following PRISMA guidelines. Experimental studies conducted with human participants were included. A random-effects inverse-variance meta-analysis was performed on standardized mean differences (SMD) of food intake (behavioral outcome) between the food advertisement and nonfood advertisement conditions of each study. Subgroup analyses were performed by age, BMI group, study design, and advertising media type. A seed-based d mapping meta-analysis of neuroimaging studies was performed to evaluate neural activity between experimental conditions. Nineteen articles were eligible for inclusion, 13 for food intake (n = 1303) and 6 for neural activity (n = 303). The pooled analysis of food intake revealed small, but statistically significant, effects of increased intake after viewing food advertising compared with the control condition among adults and children (adult SMD: 0.16; 95% CI: 0.03, 0.28; P = 0.01; I² = 0; 95% CI: 0, 95.0%; Children SMD: 0.25; 95% CI: 0.14, 0.37; P < 0.0001; I² = 60.4%; 95% CI: 25.6%, 79.0%). The neuroimaging studies involved children only, and the pooled analysis corrected for multiple comparisons identified one significant cluster, the middle occipital gyrus, with increased activity after food advertising exposure compared with the control condition (peak coordinates: 30, -86, 12; z-value: 6.301, size: 226 voxels; P < 0.001). These findings suggest that acute exposure to food advertising increases food intake among children and adults and that the middle occipital gyrus is an implicated brain region among children. (PROSPERO registration: CRD42022311357).

The relationship between sleep and appetitive conditioning: A systematic review and meta-analysis

This systematic review and meta-analysis (PROSPERO registration animal/human studies: CRD42021234793/CRD42021234790) examined the relationship between sleep and appetitive conditioning. Inclusion criteria included: a) appetitive conditioning paradigm; b) measure of conditioning; c) sleep measurement and/or sleep loss; d) human and/etor non-human animal samples; and e) written in English. Searches of seven databases returned 3777 publications. The final sample consisted of 42 studies using primarily animal samples and involving food- and drug-related conditioning tasks. We found sleep loss disrupted appetitive conditioning of food rewards (p < 0.001) but potentiated appetitive conditioning of drug rewards (p < 0.001). Furthermore, sleep loss negatively impacted extinction learning irrespective of the reward type. Post-learning sleep was associated with increases in REM sleep (p = 0.02). Findings suggest sleep loss potentiates the impact of psychoactive substances in a manner likely to produce an increased risk of problematic substance use. In obese/overweight populations, sleep loss may be associated with deficits in the conditioning and extinction of reward-related behaviours. Further research should assess the relationship between sleep and appetitive conditioning in humans.

Habituation or sensitization of brain response to food cues: Temporal dynamic analysis in an functional magnetic resonance imaging study

Introduction

In the modern obesogenic environment, heightened reactivity to food-associated cues plays a major role in overconsumption by evoking appetitive responses. Accordingly, functional magnetic resonance imaging (fMRI) studies have implicated regions of the salience and rewards processing in this dysfunctional food cue-reactivity, but the temporal dynamics of brain activation (sensitization or habituation over time) remain poorly understood.

Methods

Forty-nine obese or overweight adults were scanned in a single fMRI session to examine brain activation during the performance of a food cue-reactivity task. A general linear model (GLM) was used to validate the activation pattern of food cue reactivity in food > neutral contrast. The linear mixed effect models were used to examine the effect of time on the neuronal response during the paradigm of food cue reactivity. Neuro-behavioral relationships were investigated with Pearson's correlation tests and group factor analysis (GFA).

Results

A linear mixed-effect model revealed a trend for the time-by-condition interactions in the left medial amygdala [t(289) = 2.21, β = 0.1, P = 0.028], right lateral amygdala [t(289) = 2.01, β = 0.26, P = 0.045], right nucleus accumbens (NAc) [t(289) = 2.81, β = 0.13, P = 0.005] and left dorsolateral prefrontal cortex (DLPFC) [t(289) = 2.58, β = 0.14, P = 0.01], as well as in the left superior temporal cortex [42 Area: t(289) = 2.53, β = 0.15, P = 0.012; TE1.0_TE1.2 Area: t(289) = 3.13, β = 0.27, P = 0.002]. Habituation of blood-oxygenation-level-dependent (BOLD) signal during exposure to food vs. neutral stimuli was evident in these regions. We have not found any area in the brain with significant increased response to food-related cues over time (sensitization). Our results elucidate the temporal dynamics of cue-reactivity in overweight and obese individuals with food-induced craving. Both subcortical areas involved in reward processing and cortical areas involved in inhibitory processing are getting habituated over time in response to food vs. neutral cues. There were significant bivariate correlations between self-report behavioral/psychological measures with individual habituation slopes for the regions with dynamic activity, but no robust cross-unit latent factors were identified between the behavioral, demographic, and self-report psychological groups.

Discussion

This work provides novel insights into dynamic neural circuit mechanisms supporting food cue reactivity, thereby suggesting pathways in biomarker development and cue-desensitization interventions.

The role of reinforcement learning and value-based decision-making frameworks in understanding food choice and eating behaviors

The obesogenic food environment includes easy access to highly-palatable, energy-dense, "ultra-processed" foods that are heavily marketed to consumers; therefore, it is critical to understand the neurocognitive processes the underlie overeating in response to environmental food-cues (e.g., food images, food branding/advertisements). Eating habits are learned through reinforcement, which is the process through which environmental food cues become valued and influence behavior. This process is supported by multiple behavioral control systems (e.g., Pavlovian, Habitual, Goal-Directed). Therefore, using neurocognitive frameworks for reinforcement learning and value-based decision-making can improve our understanding of food-choice and eating behaviors. Specifically, the role of reinforcement learning in eating behaviors was considered using the frameworks of (1) Sign-versus Goal-Tracking Phenotypes; (2) Model-Free versus Model-Based; and (3) the Utility or Value-Based Model. The sign-and goal-tracking phenotypes may contribute a mechanistic insight on the role of food-cue incentive salience in two prevailing models of overconsumption-the Extended Behavioral Susceptibility Theory and the Reactivity to Embedded Food Cues in Advertising Model. Similarly, the model-free versus model-based framework may contribute insight to the Extended Behavioral Susceptibility Theory and the Healthy Food Promotion Model. Finally, the value-based model provides a framework for understanding how all three learning systems are integrated to influence food choice. Together, these frameworks can provide mechanistic insight to existing models of food choice and overconsumption and may contribute to the development of future prevention and treatment efforts.