Neural mechanisms associated with food motivation in obese and healthy weight adults

Operant Training for Highly Palatable Food Alters Translating Messenger RNA in Nucleus Accumbens D2 Neurons and Reveals a Modulatory Role of Ncdn

BACKGROUND

Highly palatable food triggers behavioral responses including strong motivation. These effects involve the reward system and dopamine neurons, which modulate neurons in the nucleus accumbens (NAc). The molecular mechanisms underlying the long-lasting effects of highly palatable food on feeding behavior are poorly understood.

METHODS

We studied the effects of 2-week operant conditioning of mice with standard or isocaloric highly palatable food. We investigated the behavioral responses and dendritic spine modifications in the NAc. We compared the translating messenger RNA in NAc neurons identified by the type of dopamine receptors they express, depending on the kind of food and training. We tested the consequences of invalidation of an abundant downregulated gene, Ncdn.

RESULTS

Operant conditioning for highly palatable food increased motivation for food even in well-fed mice. In wild-type mice, free choice between regular and highly palatable food increased weight compared with access to regular food only. Highly palatable food increased spine density in the NAc. In animals trained for highly palatable food, translating messenger RNAs were modified in NAc neurons expressing dopamine D2 receptors, mostly corresponding to striatal projection neurons, but not in neurons expressing D1 receptors. Knockout of Ncdn, an abundant downregulated gene, opposed the conditioning-induced changes in satiety-sensitive feeding behavior and apparent motivation for highly palatable food, suggesting that downregulation may be a compensatory mechanism.

CONCLUSIONS

Our results emphasize the importance of messenger RNA alterations in D2 striatal projection neurons in the NAc in the behavioral consequences of highly palatable food conditioning and suggest a modulatory contribution of Ncdn downregulation.

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.

Exposure to written content eliciting weight stigmatization: Neural responses in appetitive and food reward regions

OBJECTIVE

Neural activity in food reward- and appetite-related regions was examined in response to high-calorie (HC), low-calorie, and non-food pictures after exposure to written weight stigma (WS) content. Relationships with eating behavior (by Three-Factor Eating Questionnaire [TFEQ]), blood glucose, and subjective appetite were also explored.

METHODS

Adults with overweight and obesity were randomized to read either a WS (n = 20) or control (n = 20) article and subsequently underwent brain scans while they rated pleasantness of food pictures. Fasting glucose, TFEQ, stigma experiences, and appetite were measured before reading the article, appetite after reading, and glucose and appetite again after the scan.

RESULTS

A priori region of interest analyses revealed significant group differences in activation to HC > low-calorie food cues in the caudate and thalamus whereas exploratory whole-brain analyses suggested significant differences in regions including left insula, left thalamus, left inferior temporal gyrus, right lingual gyrus, and bilateral middle occipital gyrus and superior parietal lobule (p < 0.005 uncorrected, k ≥ 200 m3 ). No significant relationships were observed between the pattern of activation and TFEQ, glucose, or subjective appetite in the WS group.

CONCLUSIONS

Exposure to WS was associated with increased responsiveness to HC food content in the dorsal striatum and thalamus in individuals with overweight and obesity.

Prefrontal cortex melanocortin 4 receptors (MC4R) mediate food intake behavior in male mice

BACKGROUND

Melanocortin 4 receptor (MC4R) activity in the hypothalamus is crucial for regulation of metabolism and food intake. The peptide ligands for the MC4R are associated with feeding, energy expenditure, and also with complex behaviors that orchestrate energy intake and expenditure, but the downstream neuroanatomical and neurochemical targets associated with these behaviors are elusive. In addition to strong expression in the hypothalamus, the MC4R is highly expressed in the medial prefrontal cortex, a region involved in executive function and decision-making.

METHODS

Using viral techniques in genetically modified male mice combined with molecular techniques, we identify and define the effects on feeding behavior of a novel population of MC4R expressing neurons in the infralimbic (IL) region of the cortex.

RESULTS

Here, we describe a novel population of MC4R-expressing neurons in the IL of the mouse prefrontal cortex that are glutamatergic, receive input from melanocortinergic neurons, and project to multiple regions that coordinate appetitive responses to food-related stimuli. The neurons are stimulated by application of MC4R-specific peptidergic agonist, THIQ. Deletion of MC4R from the IL neurons causes increased food intake and body weight gain and impaired executive function in simple food-related behavior tasks.

CONCLUSION

Together, these data suggest that MC4R neurons of the IL play a critical role in the regulation of food intake in male mice.

Binge Eating (BE) and Obesity: Brain Activity and Psychological Measures before and after Roux-En-Y Gastric Bypass (RYGB)

Brain activity in response to food cues following Roux-En-Y Gastric Bypass (RYGB) in binge eating (BE) or non-binge eating (NB) individuals is understudied. Here, 15 RYGB (8 BE; 7 NB) and 13 no treatment (NT) (7 BE; 6 NB) women with obesity underwent fMRI imaging while viewing high and low energy density food (HEF and LEF, respectively) and non-food (NF) visual cues. A region of interest (ROI) analysis compared BE participants to NB participants in those undergoing RYGB surgery pre-surgery and 4 months post. Results were corrected for multiple comparisons using liberal (p < 0.006 uncorrected) and stringent (p < 0.05 FDR corrected) thresholds. Four months following RYGB (vs. no treatment (NT) control), both BE and NB participants showed greater reductions in blood oxygen level-dependent (BOLD) signals (a proxy of local brain activity) in the dorsomedial prefrontal cortex in response to HEF (vs. LEF) cues (p < 0.006). BE (vs. NB) participants showed greater increases in the precuneus (p < 0.006) and thalamic regions (p < 0.05 corrected) to food (vs. NF). For RYGB (vs. NT) participants, BE participants, but not NB participants, showed lower BOLD signal in the middle occipital gyrus (p < 0.006), whilst NB participants, but not BE participants, showed lower signal in inferior frontal gyrus (p < 0.006) in response to HEF (vs. LEF). Results suggest distinct neural mechanisms of RGYB in BE and may help lead to improved clinical treatments.

Potential biomarker of brain response to opioid antagonism in adolescents with eating disorders: a pilot study

Background

Eating Disorders (ED) affect up to 5% of youth and are associated with reward system alterations and compulsive behaviors. Naltrexone, an opioid antagonist, is used to treat ED behaviors such as binge eating and/or purging. The presumed mechanism of action is blockade of reward activation; however, not all patients respond, and the optimal dose is unknown. Developing a tool to detect objective drug response in the brain will facilitate drug development and therapeutic optimization. This pilot study evaluated neuroimaging as a pharmacodynamic biomarker of opioid antagonism in adolescents with ED.

Methods

Youth aged 13-21 with binge/purge ED completed functional magnetic resonance imaging (fMRI) pre- and post-oral naltrexone. fMRI detected blood oxygenation-level dependent (BOLD) signal at rest and during two reward probes (monetary incentive delay, MID, and passive food view, PFV) in predefined regions of interest associated with reward and inhibitory control. Effect sizes for Δ%BOLD (post-naltrexone vs. baseline) were estimated using linear mixed effects modeling.

Results

In 12 youth (16-21 years, 92% female), BOLD signal changes were detected following naltrexone in the nucleus accumbens during PFV (Δ%BOLD -0.08 ± 0.03; Cohen's d -1.06, p = 0.048) and anterior cingulate cortex during MID (Δ%BOLD 0.06 ± 0.03; Cohen's d 1.25, p = 0.086).

Conclusion

fMRI detected acute reward pathway modulation in this small sample of adolescents with binge/purge ED. If validated in future, larger trials, task-based Δ%BOLD detected by fMRI may serve as a pharmacodynamic biomarker of opioid antagonism to facilitate the development of novel therapeutics targeting the reward pathway, enable quantitative pharmacology trials, and inform drug dosing.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT04935931, NCT#04935931.

Relation of Overweight/Obesity to Reward Region Response to Food Reward and the Moderating Effects of Parental History of Eating Pathology in Adolescent Females

OBJECTIVE

To test whether overweight/obesity is associated with an elevated reward region response to milkshake cues and a low reward region response to milkshake receipt. To test whether the risk for eating pathology moderates the effects of weight status on the neural response to milkshake cues and milkshake receipt.

METHOD

The current study used functional magnetic resonance imaging (fMRI) to examine the neuronal responses of female adolescents (n = 80; M age = 14.6 ± 0.9; M BMI = 21.9 ± 3.6; 41% with a biological parental history of eating pathology) during a food receipt paradigm.

RESULTS

Females with overweight/obesity showed a greater ventromedial prefrontal cortex (vmPFC), and ventral anterior cingulate (ACC) response to milkshake cues and a greater ventral striatum, subgenual ACC, and dorsomedial prefrontal cortex response to milkshake receipt than those with a healthy weight. Females with overweight/obesity plus a parental history of eating pathology showed a greater vmPFC/medial orbitofrontal cortex response to milkshake cues than those without a parental history of eating pathology and those with a healthy weight. Females with overweight/obesity and without a parental history of eating pathology showed a greater thalamus and striatum response to milkshake receipt.

CONCLUSIONS

Overweight/obesity is associated with an elevated reward region response to palatable food cues and food receipt. A risk for eating pathology enhances the reward region response to food cues in those with excess weight.

Evaluation of Autonomic Nervous System Dysfunction in Childhood Obesity and Prader-Willi Syndrome

The autonomic nervous system (ANS) may play a role in the distribution of body fat and the development of obesity and its complications. Features of individuals with Prader-Willi syndrome (PWS) impacted by PWS molecular genetic classes suggest alterations in ANS function; however, these have been rarely studied and presented with conflicting results. The aim of this study was to investigate if the ANS function is altered in PWS. In this case-control study, we assessed ANS function in 20 subjects with PWS (6 males/14 females; median age 10.5 years) and 27 body mass index (BMI) z-score-matched controls (19 males/8 females; median age 12.8 years). Standardized non-invasive measures of cardiac baroreflex function, heart rate, blood pressure, heart rate variability, quantitative sudomotor axon reflex tests, and a symptom questionnaire were completed. The increase in heart rate in response to head-up tilt testing was blunted (p < 0.01) in PWS compared to controls. Besides a lower heart rate ratio with Valsalva in PWS (p < 0.01), no significant differences were observed in other measures of cardiac function or sweat production. Findings suggest possible altered sympathetic function in PWS.

Cocaine-induced plasticity, motivation, and cue responsivity do not differ in obesity-prone vs obesity-resistant rats; implications for food addiction

RATIONALE

Compared to obesity-resistant rats, obesity-prone rats consume more food, work harder to obtain food, show greater motivational responses to food-cues, and show greater striatal plasticity in response to eating sugary/fatty foods. Therefore, it is possible that obesity-prone rats may also be more sensitive to the motivational properties of cocaine and cocaine-paired cues, and to plasticity induced by cocaine.

OBJECTIVE

To examine baseline differences in motivation for cocaine and effects of intermittent access (IntA) cocaine self-administration on cocaine motivation, neurobehavioral responsivity to cocaine-paired cues, and locomotor sensitization in male obesity-prone vs obesity-resistant rats.

METHODS

Intravenous cocaine self-administration was used to examine drug-taking and drug-seeking in males. Motivation for cocaine was measured using a within session threshold procedure. Cue-induced c-Fos expression in mesocorticolimbic regions was measured.

RESULTS

Drug-taking and drug-seeking, cue-induced c-Fos, locomotor sensitization, and preferred level of cocaine consumption (Q0) were similar between obesity-prone and obesity-resistant groups. Maximal responding during demand testing (Rmax) was lower in obesity-prone rats. IntA experience enhanced motivation for cocaine (Pmax) in obesity-prone rats.

CONCLUSIONS

The results do not support robust inherent differences in motivation for cocaine, cue-induced cocaine seeking, or neurobehavioral plasticity induced by IntA in obesity-prone vs obesity-resistant rats. This contrasts with previously established differences seen for food and food cues in these populations and shows that inherent enhancements in motivation for food and food-paired cues do not necessarily transfer to drugs and drug-paired cues.

Operant training for highly palatable food alters translating mRNA in nucleus accumbens D2 neurons and reveals a modulatory role of Neurochondrin

BACKGROUND

Highly palatable food triggers behavioral alterations reminiscent of those induced by addictive drugs. These effects involve the reward system and dopamine neurons, which modulate neurons in the nucleus accumbens (NAc). The molecular mechanisms underlying the effects of highly palatable food on feeding behavior are poorly understood.

METHODS

We studied the effects of 2-week operant conditioning of mice with standard or isocaloric highly palatable food. We investigated the behavioral effects and dendritic spine modifications in the NAc. We compared the translating mRNA in NAc neurons identified by the type of dopamine receptors they express, depending on the type of food and training. We tested the consequences of invalidation of an abundant downregulated gene, Ncdn (Neurochondrin).

RESULTS

Operant conditioning for highly palatable food increases motivation for food even in well-fed mice. In control mice, free access to regular or highly palatable food results in increased weight as compared to regular food only. Highly palatable food increases spine density in the NAc. In animals trained for highly palatable food, translating mRNAs are modified in NAc dopamine D2-receptor-expressing neurons, mostly corresponding to striatal projection neurons, but not in those expressing D1-receptors. Knock-out of Ncdn, an abundant down-regulated gene, opposes the conditioning-induced changes in satiety-sensitive feeding behavior and apparent motivation for highly palatable food, suggesting down-regulation may be a compensatory mechanism.

CONCLUSIONS

Our results emphasize the importance of mRNA alterations D2 striatal projection neurons in the NAc in the behavioral consequences of highly palatable food conditioning and suggest a modulatory contribution of Ncdn downregulation.

IT IS A MATTER OF PERSPECTIVE: ATTENTIONAL FOCUS RATHER THAN DIETARY RESTRAINT DRIVES BRAIN RESPONSES TO FOOD STIMULI

Brain responses to food are thought to reflect food's rewarding value and to fluctuate with dietary restraint. We propose that brain responses to food are dynamic and depend on attentional focus. Food pictures (high-caloric/low-caloric, palatable/unpalatable) were presented during fMRI-scanning, while attentional focus (hedonic/health/neutral) was induced in 52 female participants varying in dietary restraint. The level of brain activity was hardly different between palatable versus unpalatable foods or high-caloric versus low-caloric foods. Activity in several brain regions was higher in hedonic than in health or neutral attentional focus (p < 0.05, FWE-corrected). Palatability and calorie content could be decoded from multi-voxel activity patterns (p < 0.05, FDR-corrected). Dietary restraint did not significantly influence brain responses to food. So, level of brain activity in response to food stimuli depends on attentional focus, and may reflect salience, not reward value. Palatability and calorie content are reflected in patterns of brain activity.

Spatiotemporal profile of altered neural reactivity to food images in obesity: Reward system is altered automatically and predicts efficacy of weight loss intervention

Introduction

Obesity presents a significant public health problem. Brain plays a central role in etiology and maintenance of obesity. Prior neuroimaging studies have found that individuals with obesity exhibit altered neural responses to images of food within the brain reward system and related brain networks. However, little is known about the dynamics of these neural responses or their relationship to later weight change. In particular, it is unknown if in obesity, the altered reward response to food images emerges early and automatically, or later, in the controlled stage of processing. It also remains unclear if the pretreatment reward system reactivity to food images is predictive of subsequent weight loss intervention outcome.

Methods

In this study, we presented high-calorie and low-calorie food, and nonfood images to individuals with obesity, who were then prescribed lifestyle changes, and matched normal-weight controls, and examined neural reactivity using magnetoencephalography (MEG). We performed whole-brain analysis to explore and characterize large-scale dynamics of brain systems affected in obesity, and tested two specific hypotheses: (1) in obese individuals, the altered reward system reactivity to food images occurs early and automatically, and (2) pretreatment reward system reactivity predicts the outcome of lifestyle weight loss intervention, with reduced activity associated with successful weight loss.

Results

We identified a distributed set of brain regions and their precise temporal dynamics that showed altered response patterns in obesity. Specifically, we found reduced neural reactivity to food images in brain networks of reward and cognitive control, and elevated reactivity in regions of attentional control and visual processing. The hypoactivity in reward system emerged early, in the automatic stage of processing (< 150 ms post-stimulus). Reduced reward and attention responsivity, and elevated neural cognitive control were predictive of weight loss after six months in treatment.

Discussion

In summary, we have identified, for the first time with high temporal resolution, the large-scale dynamics of brain reactivity to food images in obese versus normal-weight individuals, and have confirmed both our hypotheses. These findings have important implications for our understanding of neurocognition and eating behavior in obesity, and can facilitate development of novel integrated treatment strategies, including tailored cognitive-behavioral and pharmacological therapies.

More complex than you might think: Neural representations of food reward value in obesity

Obesity reached pandemic proportions and weight-loss treatments are mostly ineffective. The level of brain activity in the reward circuitry is proposed to be proportionate to the reward value of food stimuli, and stronger in people with obesity. However, empirical evidence is inconsistent. This may be due to the double-sided nature of high caloric palatable foods: at once highly palatable and high in calories (unhealthy). This study hypothesizes that, viewing high caloric palatable foods, a hedonic attentional focus compared to a health and a neutral attentional focus elicits more activity in reward-related brain regions, mostly in people with obesity. Moreover, caloric content and food palatability can be decoded from multivoxel patterns of activity most accurately in people with obesity and in the corresponding attentional focus. During one fMRI-session, attentional focus (hedonic, health, neutral) was manipulated using a one-back task with individually tailored food stimuli in 32 healthy-weight people and 29 people with obesity. Univariate analyses (p < 0.05, FWE-corrected) showed that brain activity was not different for palatable vs. unpalatable foods, nor for high vs. low caloric foods. Instead, this was higher in the hedonic compared to the health and neutral attentional focus. Multivariate analyses (MVPA) (p < 0.05, FDR-corrected) showed that palatability and caloric content could be decoded above chance level, independently of either BMI or attentional focus. Thus, brain activity to visual food stimuli is neither proportionate to the reward value (palatability and/or caloric content), nor significantly moderated by BMI. Instead, it depends on people's attentional focus, and may reflect motivational salience. Furthermore, food palatability and caloric content are represented as patterns of brain activity, independently of BMI and attentional focus. So, food reward value is reflected in patterns, not levels, of brain activity.

A randomized, double-blind, placebo-controlled clinical trial of 8-week intranasal oxytocin administration in adults with obesity: Rationale, study design, and methods

BACKGROUND

Obesity affects more than one-third of adults in the U.S., and effective treatment options are urgently needed. Oxytocin administration induces weight loss in animal models of obesity via effects on caloric intake, energy expenditure, and fat metabolism. We study intranasal oxytocin, an investigational drug shown to reduce caloric intake in humans, as a potential novel treatment for obesity.

METHODS

We report the rationale, design, methods, and biostatistical analysis plan of a randomized, double-blind, placebo-controlled clinical trial of intranasal oxytocin for weight loss (primary endpoint) in adults with obesity. Participants (aged 18-45 years) were randomly allocated (1:1) to oxytocin (four times daily over eight weeks) versus placebo. Randomization was stratified by biological sex and BMI (30 to <35, 35 to <40, ≥40 kg/m2). We investigate the efficacy, safety, and mechanisms of oxytocin administration in reducing body weight. Secondary endpoints include changes in resting energy expenditure, body composition, caloric intake, metabolic profile, and brain activation via functional magnetic resonance imaging in response to food images and during an impulse control task. Safety and tolerability (e.g., review of adverse events, vital signs, electrocardiogram, comprehensive metabolic panel) are assessed throughout the study and six weeks after treatment completion.

RESULTS

Sixty-one male and female participants aged 18-45 years were randomized (mean age 34 years, mean BMI 37 kg/m2). The study sample is diverse with 38% identifying as non-White and 20% Hispanic.

CONCLUSION

Investigating intranasal oxytocin's efficacy, safety, and mechanisms as an anti-obesity medication will advance the search for optimal treatment strategies for obesity and its associated severe sequelae.

Neural structural abnormalities behind altered brain activation in obesity: Evidence from meta-analyses of brain activation and morphometric data

Obesity represents a risk factor for disability with a major bearing on life expectancy. Neuroimaging techniques are contributing to clarify its neurobiological underpinnings. Here, we explored whether structural brain abnormalities might accompany altered brain activations in obesity. We combined and compared data from brain activation studies for food stimuli and the data reported in structural voxel-based morphometry studies. We found that obese individuals have reduced grey matter density and functional activations in the thalamus and midbrain. A functional connectivity analysis based on these two clusters and its quantitative decoding showed that these regions are part of the reward system functional brain network. Moreover, we found specific grey matter hypo-densities in prefrontal cortex for the obese subjects, regions involved in controlled behaviour. These results support theories of obesity that point to reduced bottom-up reward processes (i.e., the Reward Deficit Theory), but also top-down theories postulating a deficit in cognitive control (i.e., the Inhibitory Control Deficit Theory). The same results also warrant a more systematic exploration of obesity whereby the reward of food and the intentional control over consummatory behaviour is manipulated.

Food cue reactivity in successful laparoscopic gastric banding: A sham-deflation-controlled pilot study

Laparoscopic adjustable gastric banding (LAGB) offers a unique opportunity to examine the underlying neuronal mechanisms of surgically assisted weight loss due to its instant, non-invasive, adjustable nature. Six participants with stable excess weight loss (%EWL ≥ 45) completed 2 days of fMRI scanning 1.5-5 years after LAGB surgery. In a within-subject randomized sham-controlled design, participants underwent (sham) removal of ∼ 50% of the band's fluid. Compared to sham-deflation (i.e., normal band constriction) of the band, in the deflation condition (i.e., decreasing restriction) participants showed significantly lower activation in the anterior (para)cingulate, angular gyrus, lateral occipital cortex, and frontal cortex in response to food images (p < 0.05, whole brain TFCE-based FWE corrected). Higher activation in the deflation condition was seen in the fusiform gyrus, inferior temporal gyrus, lingual gyrus, lateral occipital cortex. The findings of this within-subject randomized controlled pilot study suggest that constriction of the stomach through LAGB may indirectly alter brain activation in response to food cues. These neuronal changes may underlie changes in food craving and food preference that support sustained post-surgical weight-loss. Despite the small sample size, this is in agreement with and adds to the growing literature of post-bariatric surgery changes in behavior and control regions.

Computational approaches to predicting treatment response to obesity using neuroimaging

Obesity is a worldwide disease associated with multiple severe adverse consequences and comorbid conditions. While an increased body weight is the defining feature in obesity, etiologies, clinical phenotypes and treatment responses vary between patients. These variations can be observed within individual treatment options which comprise lifestyle interventions, pharmacological treatment, and bariatric surgery. Bariatric surgery can be regarded as the most effective treatment method. However, long-term weight regain is comparably frequent even for this treatment and its application is not without risk. A prognostic tool that would help predict the effectivity of the individual treatment methods in the long term would be essential in a personalized medicine approach. In line with this objective, an increasing number of studies have combined neuroimaging and computational modeling to predict treatment outcome in obesity. In our review, we begin by outlining the central nervous mechanisms measured with neuroimaging in these studies. The mechanisms are primarily related to reward-processing and include "incentive salience" and psychobehavioral control. We then present the diverse neuroimaging methods and computational prediction techniques applied. The studies included in this review provide consistent support for the importance of incentive salience and psychobehavioral control for treatment outcome in obesity. Nevertheless, further studies comprising larger sample sizes and rigorous validation processes are necessary to answer the question of whether or not the approach is sufficiently accurate for clinical real-world application.

Food cue reactivity: Neurobiological and behavioral underpinnings

The modern obesogenic environment contains an abundance of food cues (e.g., sight, smell of food) as well cues that are associated with food through learning and memory processes. Food cue exposure can lead to food seeking and excessive consumption in otherwise food-sated individuals, and a high level of food cue responsivity is a risk factor for overweight and obesity. Similar food cue responses are observed in experimental rodent models, and these models are therefore useful for mechanistically identifying the neural circuits mediating food cue responsivity. This review draws from both experimental rodent models and human data to characterize the behavioral and biological processes through which food-associated stimuli contribute to overeating and weight gain. Two rodent models are emphasized - cue-potentiated feeding and Pavlovian-instrumental transfer - that provide insight in the neural circuits and peptide systems underlying food cue responsivity. Data from humans are highlighted that reveal physiological, psychological, and neural mechanisms that connect food cue responsivity with overeating and weight gain. The collective literature identifies connections between heightened food cue responsivity and obesity in both rodents and humans, and identifies underlying brain regions (nucleus accumbens, amygdala, orbitofrontal cortex, hippocampus) and endocrine systems (ghrelin) that regulate food cue responsivity in both species. These species similarities are encouraging for the possibility of mechanistic rodent model research and further human research leading to novel treatments for excessive food cue responsivity in humans.

Altered neural correlates of episodic memory for food and non-food cues in females with overweight/obesity

Episodic memory formation is fundamental to cognition and plays a key role in eating behaviors, indirectly promoting the maintenance and acceleration of weight gain. Impaired episodic memory function is a hallmark of people with overweight/obesity, nevertheless, little research has been conducted to explore the effects of overweight/obesity on neural networks associated with episodic memory. The current study aimed to unravel the behavioral responses and neurocognitive mechanisms underlying the episodic memory for food and non-food cues in females with overweight/obesity. To explore this issue, a group of females with overweight/obesity (n = 26) and a group of age-matched females with healthy weight (n = 28) participated in a functional magnetic resonance imaging (fMRI) event-related episodic memory paradigm, during which pictures of palatable food and pictures of neutral daily necessities were presented. Whole-brain analyses revealed differential engagement in several neural regions between the groups during an episodic memory task. Specifically, compared to the healthy weight controls, females with overweight/obesity exhibited reduced brain activity in the temporal, parietal, and frontal regions during episodic memory encoding and successful retrieval of both food and non-food cues. Additionally, activation patterns in the left hippocampus and right olfactory cortex of females with and without overweight/obesity suggested that item memory changed according to the type of stimuli presented during item memory. Specifically, females with overweight/obesity showed greater engagement of the left hippocampus and right olfactory cortex when processing food cues, but less activation of the left hippocampus and right olfactory cortex when presented with non-food cues. Consistent with the obesity and suboptimal food-related decision theoretical model, these findings provide evidence of dissociation of the neural underpinnings of episodic memory in females with overweight/obesity and underline important effects of overweight/obesity on brain functions related to episodic memory.

Impaired Brain Satiety Responses After Weight Loss in Children With Obesity

CONTEXT

Obesity interventions often result in increased motivation to eat.

OBJECTIVE

We investigated relationships between obesity outcomes and changes in brain activation by visual food cues and hormone levels in response to obesity intervention by family-based behavioral treatment (FBT).

METHODS

Neuroimaging and hormone assessments were conducted before and after 24-week FBT intervention in children with obesity (OB, n = 28), or children of healthy weight without intervention (HW, n = 17), all 9- to 11-year-old boys and girls. We evaluated meal-induced changes in neural activation to high- vs low-calorie food cues across appetite-processing brain regions and gut hormones.

RESULTS

Among children with OB who underwent FBT, greater declines of BMI z-score were associated with lesser reductions after the FBT intervention in meal-induced changes in neural activation to high- vs low-calorie food cues across appetite-processing brain regions (P < 0.05), and the slope of relationship was significantly different compared with children of HW. In children with OB, less reduction in brain responses to a meal from before to after FBT was associated with greater meal-induced reduction in ghrelin and increased meal-induced stimulation in peptide YY and glucagon-like peptide-1 (all P < 0.05).

CONCLUSION

In response to FBT, adaptations of central satiety responses and peripheral satiety-regulating hormones were noted. After weight loss, changes of peripheral hormone secretion support weight loss, but there was a weaker central satiety response. The findings suggest that even when peripheral satiety responses by gut hormones are intact, the central regulation of satiety is disturbed in children with OB who significantly improve their weight status during FBT, which could favor future weight regain.

A systematic and meta-analytic review on the neural correlates of viewing high- and low-calorie foods among normal-weight adults

In the context of current-day online shopping, people select foods based on pictures and using their visual systems. Although there are some reviews of previous neuroimaging studies on appetitive behaviors, the findings on neural activation in response to pictures of high- and low-calorie foods seem inconsistent. This study aims to systematically review, integrate, and meta-analyze neuroimaging evidence of viewing high- and low-calorie foods. There were 25 samples from 24 studies, totalizing 489 normal-weight participants (311 female, 160 male, and 18 of unknown sex). We conducted a systematic review and Activation Likelihood Estimation (ALE) meta-analysis on viewing high-calorie foods (versus non-foods), low-calorie foods (versus non-foods), and high- versus low-calorie foods. In systematic review, several brain regions were shown to be activated when viewing high- or low-calorie foods (versus non-foods) and viewing high- versus low-calorie foods, including the prefrontal cortex, orbitofrontal cortex, amygdala, insula, ventral striatum, hippocampus, superior parietal lobe, and fusiform gyrus. However, the ALE meta-analysis showed that the left orbitofrontal cortex, left amygdala, insula, superior parietal lobe, and fusiform gyrus were activated when viewing high-calorie foods (versus non-foods); the left fusiform gyrus was activated when viewing low-calorie foods (versus non-foods); and no cluster was activated when viewing high- versus low-calorie foods. Our research suggests an appetitive brain network that includes visual perception and attentional processing, sensory input integration, subjective reward value encoding, decision-making, and top-down cognitive control. Future studies should control for the effects of methodological and physiological variables when examining the neural correlates of viewing high- and low-calorie foods.

Effects of mindset on hormonal responding, neural representations, subjective experience and intake

A person can alternate between food-related mindsets, which in turn may depend on one's emotional state or situation. Being in a certain mindset can influence food-related thoughts, but interestingly it might also affect eating-related physiological responses. The current study investigates the influence of an induced 'loss of control' mindset as compared to an 'in control' mindset on hormonal, neural and behavioural responses to chocolate stimuli. Mindsets were induced by having female chocolate lovers view a short movie during two sessions in a within-subjects design. Neural responses to visual chocolate stimuli were measured using an ultra-high field (7T) scanner. Momentary ghrelin and glucagon-like peptide 1 (GLP-1) levels were determined on five moments and were simultaneously assessed with self-reports on perceptions of chocolate craving, hunger and feelings of control. Furthermore, chocolate intake was measured using a bogus chocolate taste test. It was hypothesized that the loss of control mindset would lead to hormonal, neural and behavioural responses that prepare for ongoing food intake, even after eating, while the control mindset would lead to responses reflecting satiety. Results show that neural activity in the mesocorticolimbic system was stronger for chocolate stimuli than for neutral stimuli and that ghrelin and GLP-1 levels responded to food intake, irrespective of mindset. Self-reported craving and actual chocolate intake were affected by mindset, in that cravings and intake were higher with a loss of control mindset than with a control mindset. Interestingly, these findings suggest that physiology on the one hand (hormonal and neural responses) and behavior and subjective experience (food intake and craving) on the other hand are not in sync, are not equally affected by mindset.

Altered regional grey matter volume and appetite-related hormone levels in adolescent obesity with or without binge-eating disorder

PURPOSE

Binge eating disorder (BED) is characterized by frequent and persistent overeating episodes of binge eating without compensatory behaviors. The aim was to evaluate regional gray matter volume (GMV) abnormalities and appetite-regulating hormone levels (NPY and Leptin) in obese subjects either with or without BED compared to healthy controls (HC).

METHODS

Twenty-six obese patients with BED, 25 obese patients without BED and 27 healthy subjects as an age-matched control group with neuroimaging and appetite-regulating hormone levels were found eligible for regional GMV abnormalities. A structural magnetic resonance scan and timely blood samples were drawn to assess the appetite-regulating hormone levels.

RESULTS

The BED obese patients had a greater GMVs of the right medial orbitofrontal cortex (OFC) and the left medial OFC compared to the non-BED obese patients. BED patients were characterized by greater GMV of the left medial OFC than HCs. Relative to the HCs, higher serum NPY levels were found in BED obese and non-BED obese groups. Serum leptin levels (pg/mL) had positively correlations with GMV in right medial OFC, left medial OFC, right lateral OFC, and left anterior cingulate cortex.

CONCLUSION

Among the reward processing network, which is largely associated with feeding behaviours in individuals with obesity and binge eating disorder, the OFC volumes was correlated with serum leptin concentrations. The results of our study may provide a rationale for exploring the link between regional grey matter volumes and appetite-related hormone levels in people with BED.

LEVEL OF EVIDENCE

Level III, case-control analytic study.

Neural underpinnings of food choice and consumption in obesity

BACKGROUND/OBJECTIVES

Obesity is associated with unhealthy food choices. Food selection is driven by the subjective valuation of available options, and the perceived and actual rewards accompanying consumption. These cognitive operations are mediated by brain regions including the ventromedial prefrontal cortex (vmPFC), dorsal anterior cingulate cortex (dACC), and ventral striatum (vStr). This study investigated the relationship between body mass index (BMI) and functional activations in the vmPFC, dACC, and vStr during food selection and consumption.

SUBJECTS/METHODS

After overnight fasting, 26 individuals (BMI: 18-40 kg/m²) performed a food choice task while being scanned with functional magnetic resonance imaging (fMRI). Each trial involved selecting one beverage from a pair of presented options, followed by delivery of a 3 mL aliquot of the selected option using an MR-compatible gustometer. We also tracked subjective preference for each beverage throughout the experiment.

RESULTS

During food choice, individuals with greater BMI had less activation in the dorsolateral prefrontal cortex when selecting a high-value option and less vmPFC activation upon its consumption. Independent of BMI, during food choice the dACC and anterior insula elicited higher activation when a less preferred beverage was selected. Activation of the dACC and a broader frontoparietal network was also observed when deciding between options more similar in value. During consumption, receipt of a more preferred beverage was associated with greater vmPFC response, and attenuation of the dACC.

CONCLUSIONS

An individual's preference for a food option modulates the brain activity associated with choosing and consuming it. The relationship between food preference and underlying brain activity is altered in obesity, with reduced engagement of cognition-related regions when presented with a highly valued option, but a blunted response in reward-related regions upon consumption.

The Association between Body Mass Index and Intra-Cortical Myelin: Findings from the Human Connectome Project

Intra-cortical myelin is a myelinated part of the cerebral cortex that is responsible for the spread and synchronization of neuronal activity in the cortex. Recent animal studies have established a link between obesity and impaired oligodendrocyte maturation vis-à-vis cells that produce and maintain myelin; however, the association between obesity and intra-cortical myelination remains to be established. To investigate the effects of obesity on intra-cortical myelin in living humans, we employed a large, demographically well-characterized sample of healthy young adults drawn from the Human Connectome Project (n = 1066). Intra-cortical myelin was assessed using a novel T1-w/T2-w ratio method. Linear regression analysis was used to investigate the association between body mass index (BMI), an indicator of obesity, and intra-cortical myelination, adjusting for covariates of no interest. We observed BMI was related to lower intra-cortical myelination in regions previously identified to be involved in reward processing (i.e., medial orbitofrontal cortex, rostral anterior cingulate cortex), attention (i.e., visual cortex, inferior/middle temporal gyrus), and salience detection (i.e., insula, supramarginal gyrus) in response to viewing food cues (corrected p < 0.05). In addition, higher BMIs were associated with more intra-cortical myelination in regions associated with somatosensory processing (i.e., the somatosensory network) and inhibitory control (i.e., lateral inferior frontal gyrus, frontal pole). These findings were also replicated after controlling for key potential confounding factors including total intracranial volume, substance use, and fluid intelligence. Findings suggested that altered intra-cortical myelination may represent a novel microstructure-level substrate underlying prior abnormal obesity-related brain neural activity, and lays a foundation for future investigations designed to evaluate how living habits, such as dietary habit and physical activity, affect intra-cortical myelination.

Obesity and Sex-Related Associations With Differential Effects of Sucralose vs Sucrose on Appetite and Reward Processing: A Randomized Crossover Trial

IMPORTANCE

Nonnutritive sweeteners (NNSs) are used as an alternative to nutritive sweeteners to quench desire for sweets while reducing caloric intake. However, studies have shown mixed results concerning the effects of NNSs on appetite, and the associations between sex and obesity with reward and appetitive responses to NNS compared with nutritive sugar are unknown.

OBJECTIVE

To examine neural reactivity to different types of high-calorie food cues (ie, sweet and savory), metabolic responses, and eating behavior following consumption of sucralose (NNS) vs sucrose (nutritive sugar) among healthy young adults.

DESIGN, SETTING, AND PARTICIPANTS

In a randomized, within-participant, crossover trial including 3 separate visits, participants underwent a functional magnetic resonance imaging task measuring blood oxygen level-dependent signal in response to visual cues. For each study visit, participants arrived at the Dornsife Cognitive Neuroimaging Center of University of Southern California at approximately 8:00 am after a 12-hour overnight fast. Blood was sampled at baseline and 10, 35, and 120 minutes after participants received a drink containing sucrose, sucralose, or water to measure plasma glucose, insulin, glucagon-like peptide(7-36), acyl-ghrelin, total peptide YY, and leptin. Participants were then presented with an ad libitum meal. Participants were right-handed, nonsmokers, weight-stable for at least 3 months before the study visits, nondieters, not taking medication, and with no history of eating disorders, illicit drug use, or medical diagnoses. Data analysis was performed from March 2020 to March 2021.

INTERVENTIONS

Participants ingested 300-mL drinks containing either sucrose (75 g), sucralose (individually sweetness matched), or water (as a control).

MAIN OUTCOMES AND MEASURES

Primary outcomes of interest were the effects of body mass index (BMI) status and sex on blood oxygen level-dependent signal to high-calorie food cues, endocrine, and feeding responses following sucralose vs sucrose consumption. Secondary outcomes included neural, endocrine, and feeding responses following sucrose vs water and sucralose vs water (control) consumption, and cue-induced appetite ratings following sucralose vs sucrose (and vs water).

RESULTS

A total of 76 participants were randomized, but 2 dropped out, leaving 74 adults (43 women [58%]; mean [SD] age, 23.40 [3.96] years; BMI range, 19.18-40.27) who completed the study. In this crossover design, 73 participants each received water (drink 1) and sucrose (drink 2), and 72 participants received water (drink 1), sucrose (drink 2), and sucralose (drink 3). Sucrose vs sucralose was associated with greater production of circulating glucose, insulin, and glucagon-like peptide-1 and suppression of acyl-ghrelin, but no differences were found for peptide YY or leptin. BMI status by drink interactions were observed in the medial frontal cortex (MFC; P for interaction < .001) and orbitofrontal cortex (OFC; P for interaction = .002). Individuals with obesity (MFC, β, 0.60; 95% CI, 0.38 to 0.83; P < .001; OFC, β, 0.27; 95% CI, 0.11 to 0.43; P = .002), but not those with overweight (MFC, β, 0.02; 95% CI, -0.19 to 0.23; P = .87; OFC, β, -0.06; 95% CI, -0.21 to 0.09; P = .41) or healthy weight (MFC, β, -0.13; 95% CI, -0.34 to 0.07; P = .21; OFC, β, -0.08; 95% CI, -0.23 to 0.06; P = .16), exhibited greater responsivity in the MFC and OFC to savory food cues after sucralose vs sucrose. Sex by drink interactions were observed in the MFC (P for interaction = .03) and OFC (P for interaction = .03) after consumption of sucralose vs sucrose. Female participants had greater MFC and OFC responses to food cues (MFC high-calorie vs low-calorie cues, β, 0.21; 95% CI, 0.05 to 0.37; P = .01; MFC sweet vs nonfood cues, β, 0.22; 95% CI, 0.02 to 0.42; P = .03; OFC food vs nonfood cues, β, 0.12; 95% CI, 0.02 to 0.22; P = .03; and OFC sweet vs nonfood cues, β, 0.15; 95% CI, 0.03 to 0.27; P = .01), but male participants' responses did not differ (MFC high-calorie vs low-calorie cues, β, 0.01; 95% CI, -0.19 to 0.21; P = .90; MFC sweet vs nonfood cues, β, -0.04; 95% CI, -0.26 to 0.18; P = .69; OFC food vs nonfood cues, β, -0.08; 95% CI, -0.24 to 0.08; P = .32; OFC sweet vs nonfood cues, β, -0.11; 95% CI, -0.31 to 0.09; P = .31). A sex by drink interaction on total calories consumed during the buffet meal was observed (P for interaction = .03). Female participants consumed greater total calories (β, 1.73; 95% CI, 0.38 to 3.08; P = .01), whereas caloric intake did not differ in male participants (β, 0.68; 95% CI, -0.99 to 2.35; P = .42) after sucralose vs sucrose ingestion.

CONCLUSIONS AND RELEVANCE

These findings suggest that female individuals and those with obesity may be particularly sensitive to disparate neural responsivity elicited by sucralose compared with sucrose consumption.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02945475.

Thoughts of social distancing experiences affect food intake and hypothetical binge eating: Implications for people in home quarantine during COVID-19

BACKGROND AND RATIONALE

Social distance regulations have been suggested as one of the best ways to control and prevent the spread of COVID-19. Social connection and food are intertwined because both have played critical evolutionary roles in human survival. We tested whether the substitutability hypothesis in human motivation applies here in that cues signaling scarcity in one domain (e.g., social connection) might enhance the desire to acquire resources in another domain (e.g., food).

METHODS

We recruited 140 adults from Kaohsiung City (the largest city in southern Taiwan) to participate in a laboratory experiment. Participants were randomly assigned to receive either social distancing or neutral primes via an emotional-event recollection technique. The amount of ice cream eaten during a taste test and the self-reported likelihood of binge eating served as the dependent measures.

RESULTS

We found that, compared with controls, participants primed with social distancing consumed more ice cream in a taste test and reported a greater likelihood that they would engage in binge eating if they were placed in home quarantine.

CONCLUSIONS

We may be the first to provide experimental evidence that social distancing can enhance the desire for food. The link between social distancing and the desire for food is pertinent to understanding how strongly social distance regulations may influence weight gain. Our findings have far-reaching implications for weight control under social distance regulations for prevention and control of COVID-19.

Associations between ghrelin and leptin and neural food cue reactivity in a fasted and sated state

Food cue exposure can trigger eating. Food cue reactivity (FCR) is a conditioned response to food cues and includes physiological responses and activation of reward-related brain areas. FCR can be affected by hunger and weight status. The appetite-regulating hormones ghrelin and leptin play a pivotal role in homeostatic as well as hedonic eating. We examined the association between ghrelin and leptin levels and neural FCR in the fasted and sated state and the association between meal-induced changes in ghrelin and neural FCR, and in how far these associations are related to BMI and HOMA-IR. Data from 109 participants from three European centers (age 50±18 y, BMI 27±5 kg/m²) who performed a food viewing task during fMRI after an overnight fast and after a standardized meal were analyzed. Blood samples were drawn prior to the viewing task in which high-caloric, low-caloric and non-food images were shown. Fasting ghrelin was positively associated with neural FCR in the inferior and superior occipital gyrus in the fasted state. This was partly attributable to BMI and HOMA-IR. These brain regions are involved in visual attention, suggesting that individuals with higher fasting ghrelin have heightened attention to food cues. Leptin was positively associated with high calorie FCR in the medial prefrontal cortex (PFC) in the fasted state and to neural FCR in the left supramarginal gyrus in the fasted versus sated state, when correcting for BMI and HOMA-IR, respectively. This PFC region is involved in assessing anticipated reward value, suggesting that for individuals with higher leptin levels high-caloric foods are more salient than low-caloric foods, but foods in general are not more salient than non-foods. There were no associations between ghrelin and leptin and neural FCR in the sated state, nor between meal-induced changes in ghrelin and neural FCR. In conclusion, we show modest associations between ghrelin and leptin and neural FCR in a relatively large sample of European adults with a broad age and BMI range. Our findings indicate that people with higher leptin levels for their weight status and people with higher ghrelin levels may be more attracted to high caloric foods when hungry. The results of the present study form a foundation for future studies to test whether food intake and (changes in) weight status can be predicted by the association between (mainly fasting) ghrelin and leptin levels and neural FCR.

Increased Brain Reward Responsivity to Food-Related Odors in Obesity

OBJECTIVE

Food odors serve as powerful stimuli signaling the food quality and energy density and direct food-specific appetite and consumption. This study explored obesity-related brain activation in response to odors related to high- or low-energy-dense foods.

METHODS

Seventeen participants with obesity (BMI > 30 kg/m² ; 4 males and 13 females) and twenty-one with normal weight (BMI < 25 kg/m² ; 9 males and 12 females) underwent a functional magnetic resonance imaging scan in which they received chocolate (high-energy-dense food) and cucumber (low-energy-dense food) odor stimuli. Participants' olfactory and gustatory functions were assessed by the "Sniffin' Sticks" and "Taste Strips" tests, respectively.

RESULTS

Compared with normal-weight controls, participants with obesity had lower odor sensitivity (phenylethyl alcohol) and decreased odor discrimination ability. However, participants with obesity demonstrated greater brain activation in response to chocolate compared with cucumber odors in the bilateral inferior frontal operculum and cerebellar vermis, right ventral anterior insula extending to putamen, right middle temporal gyrus, and right supramarginal areas.

CONCLUSIONS

The present study provides preliminary evidence that obesity is associated with heightened brain activation of the reward and flavor processing areas in response to chocolate versus cucumber odors, possibly because of the higher energy density and reinforcing value of chocolate compared with cucumber.

Reassessing relationships between appetite and adiposity in people at risk of obesity: A twin study using fMRI

BACKGROUND

Neuroimaging studies suggest that appetitive drive is enhanced in obesity.

OBJECTIVE

To test if appetitive drive varies in direct proportion to the level of body adiposity after accounting for genetic factors that contribute to both brain response and obesity risk.

SUBJECTS/METHODS

Participants were adult monozygotic (n = 54) and dizygotic (n = 30) twins with at least one member of the pair with obesity. Body composition was assessed by dual-energy X-ray absorptiometry. Hormonal and appetite measures were obtained in response to a standardized meal that provided 20% of estimated daily caloric needs and to an ad libitum buffet meal. Pre- and post-meal functional magnetic resonance imaging (fMRI) assessed brain response to visual food cues in a set of a priori appetite-regulating regions. Exploratory voxelwise analyses outside a priori regions were performed with correction for multiple comparisons.

RESULTS

In a group of 84 adults, the majority with obesity (75%), body fat mass was not associated with hormonal responses to a meal (glucose, insulin, glucagon-like peptide-1 and ghrelin, all P>0.40), subjective feelings of hunger (β=-0.01 mm [95% CI -0.35, 0.34] P = 0.97) and fullness (β=0.15 mm [-0.15, 0.44] P = 0.33), or buffet meal intake in relation to estimated daily caloric needs (β=0.28% [-0.05, 0.60] P = 0.10). Body fat mass was also not associated with brain response to high-calorie food cues in appetite-regulating regions (Pre-meal β=-0.12 [-0.32, 0.09] P = 0.26; Post-meal β=0.18 [-0.02, 0.37] P = 0.09; Change by a meal β=0.29 [-0.02, 0.61] P = 0.07). Conversely, lower fat mass was associated with being weight reduced (β=-0.05% [-0.07, -0.03] P<0.001) and greater pre-meal activation to high-calorie food cues in the dorsolateral prefrontal cortex (Z = 3.63 P = 0.017).

CONCLUSIONS

In a large study of adult twins, the majority with overweight or obesity, the level of adiposity was not associated with excess appetitive drive as assessed by behavioral, hormonal, or fMRI measures.

Inter-individual body mass variations relate to fractionated functional brain hierarchies

Variations in body mass index (BMI) have been suggested to relate to atypical brain organization, yet connectome-level substrates of BMI and their neurobiological underpinnings remain unclear. Studying 325 healthy young adults, we examined associations between functional connectivity and inter-individual BMI variations. We utilized non-linear connectome manifold learning techniques to represent macroscale functional organization along continuous hierarchical axes that dissociate low level and higher order brain systems. We observed an increased differentiation between unimodal and heteromodal association networks in individuals with higher BMI, indicative of a disrupted modular architecture and hierarchy of the brain. Transcriptomic decoding and gene enrichment analyses identified genes previously implicated in genome-wide associations to BMI and specific cortical, striatal, and cerebellar cell types. These findings illustrate functional connectome substrates of BMI variations in healthy young adults and point to potential molecular associations.

Considering Sex as a Biological Variable in Basic and Clinical Studies: An Endocrine Society Scientific Statement

In May 2014, the National Institutes of Health (NIH) stated its intent to "require applicants to consider sex as a biological variable (SABV) in the design and analysis of NIH-funded research involving animals and cells." Since then, proposed research plans that include animals routinely state that both sexes/genders will be used; however, in many instances, researchers and reviewers are at a loss about the issue of sex differences. Moreover, the terms sex and gender are used interchangeably by many researchers, further complicating the issue. In addition, the sex or gender of the researcher might influence study outcomes, especially those concerning behavioral studies, in both animals and humans. The act of observation may change the outcome (the "observer effect") and any experimental manipulation, no matter how well-controlled, is subject to it. This is nowhere more applicable than in physiology and behavior. The sex of established cultured cell lines is another issue, in addition to aneuploidy; chromosomal numbers can change as cells are passaged. Additionally, culture medium contains steroids, growth hormone, and insulin that might influence expression of various genes. These issues often are not taken into account, determined, or even considered. Issues pertaining to the "sex" of cultured cells are beyond the scope of this Statement. However, we will discuss the factors that influence sex and gender in both basic research (that using animal models) and clinical research (that involving human subjects), as well as in some areas of science where sex differences are routinely studied. Sex differences in baseline physiology and associated mechanisms form the foundation for understanding sex differences in diseases pathology, treatments, and outcomes. The purpose of this Statement is to highlight lessons learned, caveats, and what to consider when evaluating data pertaining to sex differences, using 3 areas of research as examples; it is not intended to serve as a guideline for research design.

What Do You Want to Eat? Influence of Menu Description and Design on Consumer's Mind: An fMRI Study

The main objective of this research was to analyse the active regions when processing dishes with a pleasant (vs. unpleasant) design and the effect of the previously read rational (vs. emotional) description when visualising the dish. The functional magnetic resonance image technique was used for the study. The results showed that participants who visualised pleasant vs. unpleasant dishes became active in several domains (e.g., attention, cognition and reward). On the other side, visualisation of unpleasant dishes activated stronger regions linked to inhibition, rejection, and related ambiguity. We found that subjects who read rational descriptions when visualising pleasant dishes activated regions related to congruence integration, while subjects who visualised emotional descriptions showed an increased neuronal response to pleasant dishes in the regions related to memory, emotion and congruence.

Sensory cue reactivity: Sensitization in alcohol use disorder and obesity

Neuroimaging techniques to measure the function of the human brain such as electroencephalography (EEG), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI), are powerful tools for understanding the underlying neural circuitry associated with alcohol use disorder (AUD) and obesity. The sensory (visual, taste and smell) paradigms used in neuroimaging studies represent an ideal platform to investigate the connection between the different neural circuits subserving the reward/executive control systems in these disorders, which may offer a translational mechanism for novel intervention predictions. Thus, the current review provides an integrated summary of the recent neuroimaging studies that have applied cue-reactivity paradigms and neuromodulation strategies to explore underlying alterations in neural circuitry as well in treatment strategies in AUD and obesity. Finally, we discuss literature on mechanisms associated with increased alcohol sensitivity post-bariatric surgery (BS) which offers guidance for future research to use sensory percepts in elucidating the relation of reward signaling in AUD development post-BS.

Impact of Gut and Metabolic Hormones on Feeding Reward

Ingestion of food activates a cascade of endocrine responses (thereby reflecting a contemporaneous feeding status) that include the release of hormones from the gastrointestinal (GI) tract, such as cholecystokinin (CCK), glucagonlike peptide YY (PYY), peptide PP, and oleoylethanolamide, as well as suppression of ghrelin secretion. The pancreas and adipose tissue, on the other hand, release hormones that serve as a measure of the current metabolic state or the long-term energy stores, that is, insulin, leptin, and adiponectin. It is well known and intuitively understandable that these hormones target either directly (by crossing the blood-brain barrier) or indirectly (e.g., via vagal input) the "homeostatic" brainstem-hypothalamic pathways involved in the regulation of appetite. The current article focuses on yet another target of the metabolic and GI hormones that is critical in inducing changes in food intake, namely, the reward system. We discuss the physiological basis of this functional interaction, its importance in the control of appetite, and the impact that disruption of this crosstalk has on energy intake in select physiological and pathophysiological states. We conclude that metabolic and GI hormones have a capacity to strengthen or weaken a response of the reward system to a given food, and thus, they are fundamental in ensuring that feeding reward is plastic and dependent on the energy status of the organism. © 2021 American Physiological Society. Compr Physiol 11:1425-1447, 2021.

The neurobiology of abstinence-induced reward-seeking in males and females

Drugs of abuse and highly palatable foods (e.g. high fat or sweet foods) have powerful reinforcing effects, which can lead to compulsive and addictive drives to ingest these substances to the point of psychopathology and self-harm--specifically the development of Substance Use Disorder (SUD) and obesity. Both SUD and binge-like overeating can be defined as disorders in which the salience of the reward (food or drug) becomes exaggerated relative to, and at the expense of, other rewards that promote well-being. A major roadblock in the treatment of these disorders is high rates of relapse after periods of abstinence. It is common, although not universal, for cue-induced craving to increase over time with abstinence, often triggered by cues previously paired with the reinforcing substance. Accumulating evidence suggests that similar neural circuits and cellular mechanisms contribute to abstinence-induced and cue-triggered seeking of drugs and palatable food. Although much research has focused on the important role of corticolimbic circuitry in drug-seeking, our goal is to expand focus to the more recently explored hypothalamic-thalamic-striatal circuitry. Specifically, we review how connections, and neurotransmitters therein, among the lateral hypothalamus, paraventricular nucleus of the thalamus, and the nucleus accumbens contribute to abstinence-induced opioid- and (high fat or sweet) food-seeking. Given that biological sex and gonadal hormones have been implicated in addictive behavior across species, another layer to this review is to compare behaviors and neural circuit-based mechanisms of abstinence-induced opioid- or food-seeking between males and females when such data is available.

'Liking' and 'wanting' in eating and food reward: Brain mechanisms and clinical implications

It is becoming clearer how neurobiological mechanisms generate 'liking' and 'wanting' components of food reward. Mesocorticolimbic mechanisms that enhance 'liking' include brain hedonic hotspots, which are specialized subregions that are uniquely able to causally amplify the hedonic impact of palatable tastes. Hedonic hotspots are found in nucleus accumbens medial shell, ventral pallidum, orbitofrontal cortex, insula cortex, and brainstem. In turn, a much larger mesocorticolimbic circuitry generates 'wanting' or incentive motivation to obtain and consume food rewards. Hedonic and motivational circuitry interact together and with hypothalamic homeostatic circuitry, allowing relevant physiological hunger and satiety states to modulate 'liking' and 'wanting' for food rewards. In some conditions such as drug addiction, 'wanting' is known to dramatically detach from 'liking' for the same reward, and this may also occur in over-eating disorders. Via incentive sensitization, 'wanting' selectively becomes higher, especially when triggered by reward cues when encountered in vulnerable states of stress, etc. Emerging evidence suggests that some cases of obesity and binge eating disorders may reflect an incentive-sensitization brain signature of cue hyper-reactivity, causing excessive 'wanting' to eat. Future findings on the neurobiological bases of 'liking' and 'wanting' can continue to improve understanding of both normal food reward and causes of clinical eating disorders.

A Systematic Review Of Implicit Attitudes And Their Neural Correlates In Eating Behaviour

An increasing number of studies suggests that implicit attitudes toward food and body shape predict eating behaviour and characterize patients with eating disorders (EDs). However, literature has not been previously analysed, thus differences between patients with EDs and healthy controls and the level of automaticity of the processes involved in implicit attitudes are still matters of debate. The present systematic review aimed to synthetize current evidence from papers investigating implicit attitudes towards food and body in healthy and EDs populations. PubMed, EMBASE (Ovid), PsycINFO, Web of Science and Scopus were systematically screened and 183 studies using different indirect paradigms were included in the qualitative analysis. The majority of studies reported negative attitudes towards overweight/obese body images in healthy and EDs samples and weight bias as a diffuse stereotypical evaluation. Implicit food attitudes are consistently reported as valid predictors of eating behaviour. Few studies on the neurobiological correlates showed neurostimulation effects on implicit attitudes, but the automaticity at brain level of implicit evaluations remains an open area of research. In conclusion, implicit attitudes are relevant measures of eating behaviour in healthy and clinical settings, although evidence about their neural correlates is limited.

Brain-gut-microbiome interactions in obesity and food addiction

Normal eating behaviour is coordinated by the tightly regulated balance between intestinal and extra-intestinal homeostatic and hedonic mechanisms. By contrast, food addiction is a complex, maladaptive eating behaviour that reflects alterations in brain-gut-microbiome (BGM) interactions and a shift of this balance towards hedonic mechanisms. Each component of the BGM axis has been implicated in the development of food addiction, with both brain to gut and gut to brain signalling playing a role. Early-life influences can prime the infant gut microbiome and brain for food addiction, which might be further reinforced by increased antibiotic usage and dietary patterns throughout adulthood. The ubiquitous availability and marketing of inexpensive, highly palatable and calorie-dense food can further shift this balance towards hedonic eating through both central (disruptions in dopaminergic signalling) and intestinal (vagal afferent function, metabolic endotoxaemia, systemic immune activation, changes to gut microbiome and metabolome) mechanisms. In this Review, we propose a systems biology model of BGM interactions, which incorporates published reports on food addiction, and provides novel insights into treatment targets aimed at each level of the BGM axis.

A plant-based meal affects thalamus perfusion differently than an energy- and macronutrient-matched conventional meal in men with type 2 diabetes, overweight/obese, and healthy men: A three-group randomized crossover study

BACKGROUND & AIMS

Reward circuitry in the brain plays a key role in weight regulation. We tested the effects of a plant-based meal on these brain regions.

METHODS

A randomized crossover design was used to test the effects of two energy- and macronutrient-matched meals: a vegan (V-meal) and a conventional meat (M-meal) on brain activity, gastrointestinal hormones, and satiety in participants with type 2 diabetes (T2D; n = 20), overweight/obese participants (O; n = 20), and healthy controls (H; n = 20). Brain perfusion was measured, using arterial spin labeling functional brain imaging; satiety was assessed using a visual analogue scale; and plasma concentrations of gut hormones were determined at 0 and 180 min. Repeated-measures ANOVA was used for statistical analysis. Bonferroni correction for multiple comparisons was applied. The Hedge's g statistic was used to measure the effect size for means of paired difference between the times (180-0 min) and meal types (M-V meal) for each group.

RESULTS

Thalamus perfusion was the highest in patients with T2D and the lowest in overweight/obese individuals (p = 0.001). Thalamus perfusion decreased significantly after ingestion of the M-meal in men with T2D (p = 0.04) and overweight/obese men (p = 0.004), and it decreased significantly after ingestion of the V-meal in healthy controls (p < 0.001; Group x Meal x Time: F = 3.4; p = 0.035). The effect size was -0.41 (95% CI, -1.14 to 0.31; p = 0.26) for men with diabetes; -0.72 (95% CI, -1.48 to 0.01; p = 0.05) for overweight/obese men; and 0.82 (95% CI, 0.09 to 1.59; p = 0.03) for healthy men. Postprandial secretion of active GLP-1 increased after the V-meal compared with the M-meal by 42% (95% CI 25-62%; p = 0.003) in men with T2D and by 41% (95% CI 24-61%; p = 0.002) in healthy controls. Changes in thalamus perfusion after ingestion of both test meals correlated with changes in satiety (r = +0.68; p < 0.01), fasting plasma insulin (r = +0.40; p < 0.01), C-peptide (r = +0.48; p < 0.01) and amylin (r = +0.55; p < 0.01), and insulin secretion at 5 mmol/l (r = +0.77; p < 0.05).

CONCLUSIONS

The higher postprandial GLP-1 secretion after the V-meal in men with T2D, with concomitant greater satiety and changes in thalamus perfusion, suggest a potential use of plant-based meals in addressing the key pathophysiologic mechanisms of food intake regulation. Trial registration ClinicalTrials.gov number, NCT02474147.

Whole-brain functional connectivity correlates of obesity phenotypes

Dysregulated neural mechanisms in reward and somatosensory circuits result in an increased appetitive drive for and reduced inhibitory control of eating, which in turn causes obesity. Despite many studies investigating the brain mechanisms of obesity, the role of macroscale whole‐brain functional connectivity remains poorly understood. Here, we identified a neuroimaging‐based functional connectivity pattern associated with obesity phenotypes by using functional connectivity analysis combined with machine learning in a large‐scale (n ~ 2,400) dataset spanning four independent cohorts. We found that brain regions containing the reward circuit positively associated with obesity phenotypes, while brain regions for sensory processing showed negative associations. Our study introduces a novel perspective for understanding how the whole‐brain functional connectivity correlates with obesity phenotypes. Furthermore, we demonstrated the generalizability of our findings by correlating the functional connectivity pattern with obesity phenotypes in three independent datasets containing subjects of multiple ages and ethnicities. Our findings suggest that obesity phenotypes can be understood in terms of macroscale whole‐brain functional connectivity and have important implications for the obesity neuroimaging community.

Development and Pilot Testing of Standardized Food Images for Studying Eating Behaviors in Children

Food images are routinely used to investigate the cognitive and neurobiological mechanisms of eating behaviors, but there is a lack of standardized image sets for use in children, which limits cross-study comparisons. To address this gap, we developed a set of age-appropriate images that included 30 high-energy-dense (ED) foods (>2.00 kcal/g), 30 low-ED foods (<1.75 kcal/g), and 30 office supplies photographed in two amounts (i.e., "larger" and "smaller"). Preliminary testing was conducted with children (6-10 years) to assess recognition, emotional valence (1 = very sad, 5 = very happy), and excitability (1 = very bored, 5 = very excited). After the initial testing, 10 images with low recognition were replaced; thus, differences between Image Set 1 and Image Set 2 were analyzed. Thirty (n = 30, mean age 8.3 ± 1.2 years) children rated Set 1, and a different cohort of 29 children (mean age 8.1 ± 1.1 years) rated Set 2. Changes made between image sets improved recognition of low-ED foods (Set 1 = 88.3 ± 10.5% vs. Set 2 = 95.6 ± 10.6%; p < 0.0001) and office supplies (83.7 ± 10.5 vs. 93.0 ± 10.6%; p < 0.0001). For the revised image set, children recognized more high-ED foods (98.4 ± 10.6%) than low-ED foods (95.6 ± 10.6%; p < 0.05) and office supplies (93.0 ± 10.6%; p < 0.0001). Recognition also improved with age (p < 0.001). Excitability and emotional valence scores were greater for high-ED foods compared with both low-ED foods and office supplies (p < 0.0001 for both). However, child fullness ratings influenced the relationship between excitability/emotional valence and category of item (p < 0.002). At the lowest fullness level, high-ED foods were rated the highest in both excitability and emotional valence, followed by low-ED foods and then office supplies. At the highest fullness level, high-ED foods remained the highest in excitability and emotional valence, but ratings for low-ED foods and office supplies were not different. This suggests that low-ED foods were more exciting and emotionally salient (relative to office supplies) when children were hungry. Ratings of recognition, excitability, and emotional valence did not differ by image amount. This new, freely available, image set showed high recognition and expected differences between image category for emotional valence and excitability. When investigating children's responsiveness to food cues, specifically energy density, it is essential for investigators to account for potential influences of child age and satiety level.

Multivariate association between brain function and eating disorders using sparse canonical correlation analysis

Eating disorder is highly associated with obesity and it is related to brain dysfunction as well. Still, the functional substrates of the brain associated with behavioral traits of eating disorder are underexplored. Existing neuroimaging studies have explored the association between eating disorder and brain function without using all the information provided by the eating disorder related questionnaire but by adopting summary factors. Here, we aimed to investigate the multivariate association between brain function and eating disorder at fine-grained question-level information. Our study is a retrospective secondary analysis that re-analyzed resting-state functional magnetic resonance imaging of 284 participants from the enhanced Nathan Kline Institute-Rockland Sample database. Leveraging sparse canonical correlation analysis, we associated the functional connectivity of all brain regions and all questions in the eating disorder questionnaires. We found that executive- and inhibitory control-related frontoparietal networks showed positive associations with questions of restraint eating, while brain regions involved in the reward system showed negative associations. Notably, inhibitory control-related brain regions showed a positive association with the degree of obesity. Findings were well replicated in the independent validation dataset (n = 34). The results of this study might contribute to a better understanding of brain function with respect to eating disorder.

Is obesity related to enhanced neural reactivity to visual food cues? A review and meta-analysis

Theoretical work suggests that obesity is related to enhanced incentive salience of food cues. However, evidence from both behavioral and neuroimaging studies on the topic is mixed. In this work we review the literature on cue reactivity in obesity and perform a preregistered meta-analysis of studies investigating effects of obesity on brain responses to passive food pictures viewing. Further, we examine whether age influences brain responses to food cues in obesity. In the meta-analysis we included 13 studies of children and adults that investigated group differences (obese vs. lean) in responses to food vs. non-food pictures viewing. While we found no significant differences in the overall meta-analysis, we show that age significantly influences brain response differences to food cues in the left insula and the left fusiform gyrus. In the left insula, obese vs. lean brain differences in response to food cues decreased with age, while in the left fusiform gyrus the pattern was opposite. Our results suggest that there is little evidence for obesity-related differences in responses to food cues and that such differences might be mediated by additional factors that are often not considered.

Child neurobiology impacts success in family-based behavioral treatment for children with obesity

Background and Objectives:

Family-based behavioral treatment (FBT) is the recommended treatment for children with common obesity. However, there is a large variability in short- and long-term treatment response and mechanisms for unsuccessful treatment outcomes are not fully understood. In this study, we tested if brain response to visual food cues among children with obesity before treatment predicted weight or behavioral outcomes during a 6-mo. behavioral weight management program and/or long-term relative weight maintenance over a 1-year follow-up period.

Subjects and Methods:

Thirty-seven children with obesity (age 9–11y, 62% male) who entered active FBT (attended 2 or more sessions) and had outcome data. Brain activation was assessed at pre-treatment by functional magnetic resonance imaging across an a priori set of appetite-processing brain regions that included the ventral and dorsal striatum, medial orbitofrontal cortex, amygdala, substantia nigra/ventral tegmental area and insula in response to viewing food images before and after a standardized meal.

Results:

Children with more robust reductions in brain activation to high-calorie food cue images following a meal had greater declines in BMI z-score during FBT (r= 0.42; 95% CI: 0.09, 0.66; P=0.02) and greater improvements in Healthy Eating Index scores (r= −0.41; 95% CI: −0.67, −0.06; P=0.02). In whole-brain analyses, greater activation in the ventromedial prefrontal cortex, specifically by high-calorie food cues, was predictive of better treatment outcomes (whole-brain cluster corrected P=0.02). There were no significant predictors of relative weight maintenance and initial behavioral or hormonal measures did not predict FBT outcomes.

Conclusions:

Children’s brain responses to a meal prior to obesity treatment were related to treatment-based weight outcomes, suggesting that neurophysiologic factors and appetitive drive, more so than initial hormone status or behavioral characteristics, limit intervention success.

Appetitive traits as targets for weight loss: The role of food cue responsiveness and satiety responsiveness

Individuals with overweight or obesity (OW/OB) are at increased risk for significant physical and psychological comorbidities. The current treatment for OW/OB is behavioral weight loss, which provides psychoeducation on nutrition and physical activity, as well as behavior therapy skills. However, behavioral weight loss is not effective for the majority of the individuals who participate. Research suggests that overeating, or eating past nutritional needs, is one of the leading causes of weight gain. Accumulating evidence suggests that appetitive traits, such as food cue responsiveness and satiety responsiveness, are associated with overeating and weight in youth and adults. The following review presents the current literature on the relationship between food cue responsiveness, satiety responsiveness, overeating, and OW/OB. Research suggests that higher food cue responsiveness and lower satiety responsiveness are associated with overeating and OW/OB cross-sectionally and longitudinally. Emerging data suggest that food cue responsiveness and satiety responsiveness may exist along the same continuum and can be targeted to manage overeating and reduce weight. We have developed a treatment model targeting food cue responsiveness and satiety responsiveness to reduce overeating and weight and have preliminary feasibility, acceptability, and efficacy data, with testing currently being conducted in larger trials. Through programs targeting appetitive traits we hope to develop an alternative weight loss model to assist individuals with a propensity to overeat.

Insights to the neural response to food cues in class III compared with class I and II obese adults using a sample of endometrial cancer survivors seeking weight loss

Background

The rates of severe or Class III obesity (BMI ≥ 40.0 kg/m²) and endometrial cancer (EC) incidence and mortality have been increasing significantly in the United States. Adults with severe obesity are more likely to die and women with severe obesity have a higher risk of EC development and mortality than those with Class I/II obesity (BMI: 30–<40 kg/m²). However, no prior studies have evaluated the neural response to food cues by obesity severity/class in adults with or without cancer.

Methods

We conducted a functional magnetic resonance imaging visual food cue task in 85 obese Stage I EC survivors who were seeking weight loss in a lifestyle intervention at baseline. We evaluated the neural response to high-calorie vs. non-food images after an overnight fast (fasted state) and after eating a standardized meal (fed state), and grouped patients by obesity class (Class I/II: n = 38; Class III: n = 47).

Results

In the fasted state, we found increased activation in several regions including the dorsolateral prefrontal cortex (DLPFC) in Class III and Class I/II patients (whole brain cluster corrected (WBCC), p < 0.05), which was significantly higher in Class III vs. Class I/II (p < 0.05). We found decreased activation in the insula in the fasted state, which was significantly lower in Class I/II vs. Class III (p = 0.03). In the fed state, we found increased activation in the DLPFC in Class III and Class I/II (WBCC, p < 0.05). The increased activation in cognitive control/inhibition regions (DLPFC) is consistent with the summative literature; however, the decreased activation in taste information processing regions (insula) was unexpected.

Conclusions

Our results provide novel insights on food cue response between different classes of obesity and highlight the importance of targeting the DLPFC in weight loss interventions, particularly in severely obese patients. Additional studies examining food-related neural circuitry between different classes of obesity are needed.

Modeling interactions between brain function, diet adherence behaviors, and weight loss success

INTRODUCTION

Obesity is linked to altered activation in reward and control brain circuitry; however, the associated brain activity related to successful or unsuccessful weight loss (WL) is unclear.

METHODS

Adults with obesity (N = 75) completed a baseline functional magnetic resonance imaging (fMRI) scan before entering a WL intervention (ie,3-month diet and physical activity [PA] program). We conducted an exploratory analysis to identify the contributions of baseline brain activation, adherence behavior patterns, and the associated connections to WL at the conclusion of a 3-month WL intervention. Food cue-reactivity brain regions were functionally identified using fMRI to index brain activation to food vs nonfood cues. Food consumption, PA, and class attendance were collected weekly during the 3-month intervention.

RESULTS

The left middle frontal gyrus (L-MFG, BA 46) and right middle frontal gyrus (R-MFG; BA 9) were positively activated when viewing food compared with nonfood images. Structural equation modeling with bootstrapping was used to investigate a hypothesized path model and revealed the following significant paths: (1) attendance to 3-month WL, (2) R-MFG to attendance, and (3) indirect effects of R-MFG through attendance on WL.

CONCLUSION

Findings suggest that brain activation to appetitive food cues predicts future WL through mediating session attendance, diet, and PA. This study contributes to the growing evidence of the importance of food cue reactivity and self-regulation brain regions and their impact on WL outcomes.