Reward processing in obesity, substance addiction and non-substance addiction

Late Positive Potential Elicited by Monetary Reward Feedback Predicts Changes of Disordered Eating From Age 11 to Age 12 in Community-Dwelling Girls

OBJECTIVE

Early adolescence is marked by elevated psychopathology, including disrupted eating attitudes and behaviors. Reward processing is an identified mechanism in portending eating pathology, that is, aberrant reward responsivity may contribute to disrupted reward-seeking behaviors (e.g., food consuming). This literature has focused on adults or mid-to-late adolescents, with little work done on early adolescence. We examined the linkages between reward feedback processing, indexed by event-related potentials (ERPs), and changes of emerging disordered eating in community-dwelling early adolescents.

METHOD

At T1, 115 youths (66 girls, mean/SD age = 11.00/1.16 years) completed an EEG monetary reward Doors task. Youths completed the Eating Disorder Examination-Questionnaire Short at T1 and ~6 months (T2) and ~12 months (T3) after T1. In the ERP data, we isolated a reward positivity (RewP) and a late positive potential (LPP) via principal component analysis. We applied multilevel modeling to examine whether baseline ERPs interacted with Time in predicting disordered eating and whether these interactions varied by sex.

RESULTS

We found a significant Time × LPP interaction in girls but not boys. Among girls, only those with a smaller LPP toward the losses (versus wins), which might reflect suboptimal evaluation and regulatory processes in undesired situations, showed increases in disordered eating from T1 to T3.

DISCUSSION

We provided preliminary yet novel evidence concerning the prospective associations between reward processing and changes of disordered eating in early adolescents. Future studies along this line will be critical for understanding the early mechanisms of eating pathology, identifying youths at risk, and developing prevention strategies.

Influence of reinforcement learning on the inhibitory control of Internet gaming disorder

Reward processing dysfunction and inhibition control deficiency have been observed in Internet gaming disorder (IGD). However, it is still unclear whether the previous reinforcement learning depends on reward/punishment feedback influences on the cognitive inhibitory control of IGD. This study compared the differences between an IGD group and healthy people without game experiences in the probability selection task and the subsequent stop signal task by the method of behavioral experiments, in order to explore whether the reward learning ability is impaired in the IGD group. We also discuss the influence of previous reward learning on subsequent inhibition control. The results showed that (1) during the reward learning phase, the IGD group's accuracy was significantly lower than that of the control group; (2) compared with the control group, the IGD group's reaction times were longer in the transfer phase; (3) for no-go trials of the inhibitory control phase after reward learning, the accuracy of the reward-related stimulation in the IGD group was lower than that of punishment-related or neutral stimulation, but there was no significant difference among the three conditions in the control group. These findings indicated that the reinforcement learning ability of the IGD group was impaired, which further caused the abnormal response to reinforcement stimuli.

Large-scale network abnormality in behavioral addiction

BACKGROUND

Researchers have endeavored to ascertain the network dysfunction associated with behavioral addiction (BA) through the utilization of resting-state functional connectivity (rsFC). Nevertheless, the identification of aberrant patterns within large-scale networks pertaining to BA has proven to be challenging.

METHODS

Whole-brain seed-based rsFC studies comparing subjects with BA and healthy controls (HC) were collected from multiple databases. Multilevel kernel density analysis was employed to ascertain brain networks in which BA was linked to hyper-connectivity or hypo-connectivity with each prior network.

RESULTS

Fifty-six seed-based rsFC publications (1755 individuals with BA and 1828 HC) were included in the meta-analysis. The present study indicate that individuals with BAs exhibit (1) hypo-connectivity within the fronto-parietal network (FN) and hypo- and hyper-connectivity within the ventral attention network (VAN); (2) hypo-connectivity between the FN and regions of the VAN, hypo-connectivity between the VAN and regions of the FN and default mode network (DMN), hyper-connectivity between the DMN and regions of the FN; (3) hypo-connectivity between the reward system and regions of the sensorimotor network (SS), DMN and VAN; (4) hypo-connectivity between the FN and regions of the SS, hyper-connectivity between the VAN and regions of the SS.

CONCLUSIONS

These findings provide impetus for a conceptual framework positing a model of BA characterized by disconnected functional coordination among large-scale networks.

The Association between Grazing and Food Addiction: The Italian Version of the Repetitive Eating Questionnaire (Rep(Eat)-Q) and Its Relationships with Food Addiction Criteria

BACKGROUND

Among the dysfunctional eating behaviors associated with excessive food intake, a construct that is gaining increasing attention is grazing-the constant, continuous, compulsive, and repetitive consumption of small/moderate amounts of food. Furthermore, in some cases, grazing seems to indicate a dependence on food and/or eating. Currently, the Repetitive Eating Questionnaire (Rep(Eat)-Q) appears to be the only questionnaire that comprehensively measures grazing, including its repetitive and compulsive eating component. Therefore, in a sample of individuals with severe obesity, the objective of this study was twofold: (A) to evaluate the psychometric properties of the Italian version of the Rep(Eat)-Q, and (B) to analyze the association between grazing and food addiction (FA).

METHOD

A cross-sectional research design was used. A total of 402 inpatients with severe obesity (BMI > 35) were recruited. Participants underwent a series of questionnaires to investigate structural validity and convergent validity and association with FA criteria.

RESULTS

The factorial structure of the Rep(Eat)-Q is robust and showed fit indexes: CFI = 0.973; RMSEA = 0.074; 90%CI [0.056-0.091]; and SRMR = 0.029. Also, it exhibited good internal consistency and convergent validity. Furthermore, logistic regression analysis highlights a specific association between certain FA criteria and grazing.

CONCLUSIONS

The Rep(Eat)-Q can be considered to be a concise, robust, reliable, and statistically sound tool to assess repetitive eating, specifically grazing. Its strong psychometric properties offer significant advantages for both research and clinical applications. Furthermore, in a sample of individuals with severe obesity, the results suggest that individuals with problematic grazing exhibit a typical behavioral profile of subjects with FA, indicating that FA can manifest through problematic grazing as well.

Transdiagnostic considerations of the relationship between reward sensitivity and psychopathological symptoms - a cross-lagged panel analysis

BACKGROUND

Reward sensitivity constitutes a potential key mechanism regarding the etiology and maintenance of mental disorders, especially depression. However, due to a lack of longitudinal studies, the temporal dynamics are not clear yet. Although some evidence indicates that reward processing could be a transdiagnostic mechanism of disorders, these observations could be also a product of comorbidity with depression. This study aimed at investigating the temporal dynamics of reward sensitivity and the course of psychopathological symptoms in a longitudinal investigation, while taking a possible mediating role of depression into account.

METHODS

We conducted a three-wave longitudinal online survey with a 4-week interval. A total of N = 453 participants filled out all three questionnaires. Reward sensitivity was assessed with the Positive Valence System Scale-21 (PVSS-21), depression with the Patient Health Questionnaire (PHQ-9), eating disorder symptoms with the Eating Disorder Examination-Questionnaire-8 (EDE-Q-8), social anxiety with the Mini-social phobia inventory (Mini-SPIN) and alcohol consumption with the Alcohol Use Disorders Identification Test-Consumption (AUDIT-C). Cross-lagged panels and mediation analyses were calculated using path analyses.

RESULTS

Depressive and eating disorder symptoms predicted reward insensitivity at later points in time. Effects were larger from T2 to T3. A bidirectional relationship concerning social anxiety was found. Higher alcohol consumption predicted higher reward sensitivity. Depression at T2 fully mediated the association between psychopathological symptoms at T1 and reward sensitivity at T3 for social anxiety and eating disorder symptoms.

CONCLUSIONS

Our findings imply that reduced reward sensitivity seems to be a consequence rather than an antecedent of psychopathological symptoms. Comorbid depression plays a crucial role in other mental disorders regarding observed hyposensitivity towards rewards. Therefore, our results do not support a transdiagnostic notion of reward sensitivity, but they indicate a potential role of reward sensitivity for symptom persistence.

TRIAL REGISTRATION

The study was preregistered at the Open Science Framework (OSF) ( https://archive.org/details/osf-registrations-6n3s8-v1 ; registration DOI https://doi.org/10.17605/OSF.IO/6N3S8 ).

The effects of an 8-week mindful eating intervention on anticipatory reward responses in striatum and midbrain

Introduction

Accumulating evidence suggests that increased neural responses during the anticipation of high-calorie food play an important role in the tendency to overeat. A promising method for counteracting enhanced food anticipation in overeating might be mindfulness-based interventions (MBIs). However, the neural mechanisms by which MBIs can affect food reward anticipation are unclear. In this randomized, actively controlled study, the primary objective was to investigate the effect of an 8-week mindful eating intervention on reward anticipation. We hypothesized that mindful eating would decrease striatal reward anticipation responses. Additionally, responses in the midbrain-from which the reward pathways originate-were explored.

Methods

Using functional magnetic resonance imaging (fMRI), we tested 58 healthy participants with a wide body mass index range (BMI: 19-35 kg/m2), motivated to change their eating behavior. During scanning they performed an incentive delay task, measuring neural reward anticipation responses to caloric and monetary cues before and after 8 weeks of mindful eating or educational cooking (active control).

Results

Compared with the educational cooking intervention, mindful eating affected neural reward anticipation responses, with reduced caloric relative to monetary reward responses. This effect was, however, not seen in the striatum, but only in the midbrain. The secondary objective was to assess temporary and long-lasting (1 year follow-up) intervention effects on self-reported eating behavior and anthropometric measures [BMI, waist circumference, waist-to-hip-ratio (WHR)]. We did not observe effects of the mindful eating intervention on eating behavior. Instead, the control intervention showed temporary beneficial effects on BMI, waist circumference, and diet quality, but not on WHR or self-reported eating behavior, as well as long-lasting increases in knowledge about healthy eating.

Discussion

These results suggest that an 8-week mindful eating intervention may have decreased the relative salience of food cues by affecting midbrain but not striatal reward responses, without necessarily affecting regular eating behavior. However, these exploratory results should be verified in confirmatory research.The primary and secondary objectives of the study were registered in the Dutch Trial Register (NTR): NL4923 (NTR5025).

Higher body weight-dependent neural activation during reward processing

Obesity is associated with alterations in brain structure and function, particularly in areas related to reward processing. Although brain structural investigations have demonstrated a continuous association between higher body weight and reduced gray matter in well-powered samples, functional neuroimaging studies have typically only contrasted individuals from the normal weight and obese body mass index (BMI) ranges with modest sample sizes. It remains unclear, whether the commonly found hyperresponsiveness of the reward circuit can (a) be replicated in well-powered studies and (b) be found as a function of higher body weight even below the threshold of clinical obesity. 383 adults across the weight spectrum underwent functional magnetic resonance imaging during a common card-guessing paradigm simulating monetary reward. Multiple regression was used to investigate the association of BMI and neural activation in the reward circuit. In addition, a one-way ANOVA model comparing three weight groups (normal weight, overweight, obese) was calculated. Higher BMI was associated with higher reward response in the bilateral insula. This association could no longer be found when participants with obesity were excluded from the analysis. The ANOVA revealed higher activation in obese vs. lean, but no difference between lean and overweight participants. The overactivation of reward-related brain areas in obesity is a consistent finding that can be replicated in large samples. In contrast to brain structural aberrations associated with higher body weight, the neurofunctional underpinnings of reward processing in the insula appear to be more pronounced in the higher body weight range.

Neuro-Vulnerability in Energy Metabolism Regulation: A Comprehensive Narrative Review

This comprehensive narrative review explores the concept of neuro-vulnerability in energy metabolism regulation and its implications for metabolic disorders. The review highlights the complex interactions among the neural, hormonal, and metabolic pathways involved in the regulation of energy metabolism. The key topics discussed include the role of organs, hormones, and neural circuits in maintaining metabolic balance. The review investigates the association between neuro-vulnerability and metabolic disorders, such as obesity, insulin resistance, and eating disorders, considering genetic, epigenetic, and environmental factors that influence neuro-vulnerability and subsequent metabolic dysregulation. Neuroendocrine interactions and the neural regulation of food intake and energy expenditure are examined, with a focus on the impact of neuro-vulnerability on appetite dysregulation and altered energy expenditure. The role of neuroinflammation in metabolic health and neuro-vulnerability is discussed, emphasizing the bidirectional relationship between metabolic dysregulation and neuroinflammatory processes. This review also evaluates the use of neuroimaging techniques in studying neuro-vulnerability and their potential applications in clinical settings. Furthermore, the association between neuro-vulnerability and eating disorders, as well as its contribution to obesity, is examined. Potential therapeutic interventions targeting neuro-vulnerability, including pharmacological treatments and lifestyle modifications, are reviewed. In conclusion, understanding the concept of neuro-vulnerability in energy metabolism regulation is crucial for addressing metabolic disorders. This review provides valuable insights into the underlying neurobiological mechanisms and their implications for metabolic health. Targeting neuro-vulnerability holds promise for developing innovative strategies in the prevention and treatment of metabolic disorders, ultimately improving metabolic health outcomes.

Neurophysiological mechanisms underlying the differential effect of reward prospect on response selection and inhibition

Reward and cognitive control play crucial roles in shaping goal-directed behavior. Yet, the behavioral and neural underpinnings of interactive effects of both processes in driving our actions towards a particular goal have remained rather unclear. Given the importance of inhibitory control, we investigated the effect of reward prospect on the modulatory influence of automatic versus controlled processes during response inhibition. For this, a performance-contingent monetary reward for both correct response selection and response inhibition was added to a Simon NoGo task, which manipulates the relationship of automatic and controlled processes in Go and NoGo trials. A neurophysiological approach was used by combining EEG temporal signal decomposition and source localization methods. Compared to a non-rewarded control group, rewarded participants showed faster response execution, as well as overall lower response selection and inhibition accuracy (shifted speed-accuracy tradeoff). Interestingly, the reward group displayed a larger interference of the interactive effects of automatic versus controlled processes during response inhibition (i.e., a larger Simon NoGo effect), but not during response selection. The reward-specific behavioral effect was mirrored by the P3 amplitude, underlining the importance of stimulus-response association processes in explaining variability in response inhibition performance. The selective reward-induced neurophysiological modulation was associated with lower activation differences in relevant structures spanning the inferior frontal and parietal cortex, as well as higher activation differences in the somatosensory cortex. Taken together, this study highlights relevant neuroanatomical structures underlying selective reward effects on response inhibition and extends previous reports on the possible detrimental effect of reward-triggered performance trade-offs on cognitive control processes.

Central Regulation of Eating Behaviors in Humans: Evidence from Functional Neuroimaging Studies

Neuroimaging has great potential to provide insight into the neural response to food stimuli. Remarkable advances have been made in understanding the neural activity underlying food perception, not only in normal eating but also in obesity, eating disorders, and disorders of gut-brain interaction in recent decades. In addition to the abnormal brain function in patients with eating disorders compared to healthy controls, new therapies, such as neurofeedback and neurostimulation techniques, have been developed that target the malfunctioning brain regions in patients with eating disorders based on the results of neuroimaging studies. In this review, we present an overview of early and more recent research on the central processing and regulation of eating behavior in healthy and patient populations. In order to better understand the relationship between the gut and the brain as well as the neural mechanisms underlying abnormal ingestive behaviors, we also provide suggestions for future directions to enhance our current methods used in food-related neuroimaging studies.

Metabolism-related brain morphology accelerates aging and predicts neurodegenerative diseases and stroke: a UK Biobank study

Metabolic syndrome (MetS) is characterized by a constellation of metabolic risk factors, including obesity, hypertriglyceridemia, low high-density lipoprotein (HDL) levels, hypertension, and hyperglycemia, and is associated with stroke and neurodegenerative diseases. This study capitalized on brain structural images and clinical data from the UK Biobank and explored the associations of brain morphology with MetS and brain aging due to MetS. Cortical surface area, thickness, and subcortical volumes were assessed using FreeSurfer. Linear regression was used to examine associations of brain morphology with five MetS components and the MetS severity in a metabolic aging group (N = 23,676, age 62.8 ± 7.5 years). Partial least squares (PLS) were employed to predict brain age using MetS-associated brain morphology. The five MetS components and MetS severity were associated with increased cortical surface area and decreased thickness, particularly in the frontal, temporal, and sensorimotor cortex, and reduced volumes in the basal ganglia. Obesity best explained the variation of brain morphology. Moreover, participants with the most severe MetS had brain age 1-year older than those without MetS. Brain age in patients with stroke (N = 1042), dementia (N = 83), Parkinson's (N = 107), and multiple sclerosis (N = 235) was greater than that in the metabolic aging group. The obesity-related brain morphology had the leading discriminative power. Therefore, the MetS-related brain morphological model can be used for risk assessment of stroke and neurodegenerative diseases. Our findings suggested that prioritizing adjusting obesity among the five metabolic components may be more helpful for improving brain health in aging populations.

Dynamic regulation of the extracellular matrix in reward memory processes: a question of time

Substance use disorders are a global health problem with increasing prevalence resulting in significant socioeconomic burden and increased mortality. Converging lines of evidence point to a critical role of brain extracellular matrix (ECM) molecules in the pathophysiology of substance use disorders. An increasing number of preclinical studies highlight the ECM as a promising target for development of novel cessation pharmacotherapies. The brain ECM is dynamically regulated during learning and memory processes, thus the time course of ECM alterations in substance use disorders is a critical factor that may impact interpretation of the current studies and development of pharmacological therapies. This review highlights the evidence for the involvement of ECM molecules in reward learning, including drug reward and natural reward such as food, as well as evidence regarding the pathophysiological state of the brain's ECM in substance use disorders and metabolic disorders. We focus on the information regarding time-course and substance specific changes in ECM molecules and how this information can be leveraged for the development of therapeutic strategies.

Phytochemical interventions for post-traumatic stress disorder: A cluster co-occurrence network analysis using CiteSpace

OBJECTIVE

This study investigated trends in the study of phytochemical treatment of post-traumatic stress disorder (PTSD).

METHODS

The Web of Science database (2007-2022) was searched using the search terms "phytochemicals" and "PTSD," and relevant literature was compiled. Network clustering co-occurrence analysis and qualitative narrative review were conducted.

RESULTS

Three hundred and one articles were included in the analysis of published research, which has surged since 2015 with nearly half of all relevant articles coming from North America. The category is dominated by neuroscience and neurology, with two journals, Addictive Behaviors and Drug and Alcohol Dependence, publishing the greatest number of papers on these topics. Most studies focused on psychedelic intervention for PTSD. Three timelines show an "ebb and flow" phenomenon between "substance use/marijuana abuse" and "psychedelic medicine/medicinal cannabis." Other phytochemicals account for a small proportion of the research and focus on topics like neurosteroid turnover, serotonin levels, and brain-derived neurotrophic factor expression.

CONCLUSION

Research on phytochemicals and PTSD is unevenly distributed across countries/regions, disciplines, and journals. Since 2015, the research paradigm shifted to constitute the mainstream of psychedelic research thus far, leading to the exploration of botanical active ingredients and molecular mechanisms. Other studies focus on anti-oxidative stress and anti-inflammation. Please cite this article as: Gao B, Qu YC, Cai MY, Zhang YY, Lu HT, Li HX, Tang YX, Shen H. Phytochemical interventions for post-traumatic stress disorder: A cluster co-occurrence network analysis using CiteSpace. J Integr Med. 2023; Epub ahead of print.

A combined X-ray fluorescence and infrared microspectroscopy study for new insights into elemental-biomolecular obesity-induced changes in rat brain structures

The objective of our research was to determine the brain changes at the molecular and elemental levels typical of early-stage obesity. Therefore a combined approach using Fourier transform infrared micro-spectroscopy (FTIR-MS) and synchrotron radiation induced X-ray fluorescence (SRXRF) was introduced to evaluate some brain macromolecular and elemental parameters in high-calorie diet (HCD)- induced obese rats (OB, n = 6) and in their lean counterparts (L, n = 6). A HCD was found to alter the lipid- and protein- related structure and elemental composition of the certain brain areas important for energy homeostasis. The increased lipid unsaturation in the frontal cortex and ventral tegmental area, the increased fatty acyl chain length in the lateral hypothalamus and substantia nigra as well as the decreased both protein α helix to protein β- sheet ratio and the percentage fraction of β-turns and β-sheets in the nucleus accumbens were revealed in the OB group reflecting obesity-related brain biomolecular aberrations. In addition, the certain brain elements including P, K and Ca were found to differentiate the lean and obese groups at the best extent. We can conclude that HCD-induced obesity triggers lipid- and protein- related structural changes as well as elemental redistribution within various brain structures important for energy homeostasis. In addition, an approach applying combined X-ray and infrared spectroscopy was shown to be a reliable tool for identifying elemental-biomolecular rat brain changes for better understanding the interplay between the chemical and structural processes involved in appetite control.

Amygdala hyperactivation relates to eating behaviour: a potential indicator of food addiction in Prader-Willi syndrome

Prader-Willi syndrome is a rare neurodevelopmental genetic disorder characterized by various endocrine, cognitive and behavioural problems. The symptoms include an obsession for food and reduced satiety, which leads to hyperphagia and morbid obesity. Neuropsychological studies have reported that Prader-Willi patients display altered social interactions with a specific weakness in interpreting social information and responding to them, a symptom close to that observed in autism spectrum disorders. In the present case-control study, we hypothesized that brain regions associated with compulsive eating behaviour would be abnormally activated by food-related odours in Prader-Willi syndrome, as these can stimulate the appetite and induce hunger-related behaviour. We conducted a brain imaging study using the olfactory modality because odours have a high-hedonic valence and can cause stronger emotional reactions than other modalities. Further, the olfactory system is also intimately associated with the endocrine regulation of energy balance and is the most appropriate modality for studies of Prader-Willi syndrome. A total of 16 Prader-Willi participants were recruited for this study, which is a significant achievement given the low incidence rate of this rare disease. The second group of 11 control age-matched subjects also participated in the brain imaging study. In the MRI scanner, using an MRI-compatible olfactometer during 56 block sessions, we randomly presented two odours (tulip and caramel), which have different hedonic valence and a different capacity to arouse hunger-related behaviour. Our results demonstrate that Prader-Willi participants have abnormal activity in the brain reward system that regulates eating behaviour. Indeed, we found that these patients had right amygdala activity up to five times higher in response to a food odour (caramel) compared with the tulip odour. In contrast, age-matched control participants had similar activity levels in response to both odours. The amygdala activity levels were found to be associated with the severity of the hyperphagia in Prader-Willi patients. Our results provide evidence for functional alteration of the right amygdala in Prader-Willi syndrome, which is part of the brain network involved in food addiction modulated by the ghrelin and oxytocin systems, which may drive the hyperphagia. Our study provides important new insights into the functioning of emotion-related brain circuits and pathology, and it is one of the few to explore the dysfunction of the neural circuits involved in emotion and addiction in Prader-Willi syndrome. It suggests new directions for the exploration and remediation of addictive behaviours.

Reward and inhibition in obesity and cigarette smoking: Neurobiological overlaps and clinical implications

Cigarette smoking and obesity are the leading causes of premature morbidity and mortality and increase the risk of all-cause mortality four-fold when comorbid. Individuals with these conditions demonstrate neurobiological and behavioral differences regarding how they respond to rewarding stimuli or engage in inhibitory control. This narrative review examines the role of reward and inhibition in cigarette smoking and obesity independently, as well as recent research demonstrating an effect of increased body mass index (BMI) on neurocognitive function in individuals who smoke. It is possible that chronic smoking and overeating of highly palatable food, contributing to obesity, dysregulates reward neurocircuitry, subsequently leading to hypofunction of brain networks associated with inhibitory control. These brain changes do not appear to be specific to food or nicotine and, as a result, can potentiate continued cross-use. Changes to reward and inhibitory function due to increased BMI may also make cessation more difficult for those comorbid for obesity and smoking.

Neural and functional validation of fMRI-informed EEG model of right inferior frontal gyrus activity

The right inferior frontal gyrus (rIFG) is a region involved in the neural underpinning of cognitive control across several domains such as inhibitory control and attentional allocation process. Therefore, it constitutes a desirable neural target for brain-guided interventions such as neurofeedback (NF). To date, rIFG-NF has shown beneficial ability to rehabilitate or enhance cognitive functions using functional Magnetic Resonance Imaging (fMRI-NF). However, the utilization of fMRI-NF for clinical purposes is severely limited, due to its poor scalability. The present study aimed to overcome the limited applicability of fMRI-NF by developing and validating an EEG model of fMRI-defined rIFG activity (hereby termed "Electrical FingerPrint of rIFG"; rIFG-EFP). To validate the computational model, we employed two experiments in healthy individuals. The first study (n = 14) aimed to test the target engagement of the model by employing rIFG-EFP-NF training while simultaneously acquiring fMRI. The second study (n = 41) aimed to test the functional outcome of two sessions of rIFG-EFP-NF using a risk preference task (known to depict cognitive control processes), employed before and after the training. Results from the first study demonstrated neural target engagement as expected, showing associated rIFG-BOLD signal changing during simultaneous rIFG-EFP-NF training. Target anatomical specificity was verified by showing a more precise prediction of the rIFG-BOLD by the rIFG-EFP model compared to other EFP models. Results of the second study suggested that successful learning to up-regulate the rIFG-EFP signal through NF can reduce one's tendency for risk taking, indicating improved cognitive control after two sessions of rIFG-EFP-NF. Overall, our results confirm the validity of a scalable NF method for targeting rIFG activity by using an EEG probe.

Body mass index interacts with sex to predict readmission in in-patients with alcohol use disorder

A previous highly controlled pilot study revealed that body mass index (BMI) predicts outcome of in-patients with alcohol use disorder (AUD) in a sex-specific manner. We here provide translational evidence from a daily clinical routine setting and investigated whether BMI and sex interact to predict 24-month readmission risk in four naturalistic cohorts of a specialized addiction clinic (i.e., all patients admitted to the clinic from 2016 to 2020): (i) in-patients (443 males and 197 females) and (ii) day clinic patients (241 males and 103 females) with a primary diagnosis of AUD; (iii) in-patients (175 males and 98 females) and (iv) day clinic patients (174 males and 64 females) with a primary substance use disorder (SUD) other than alcohol. In the in-patients with AUD, BMI interacted with sex to predict the 24-month readmission risks (p = 0.008; after adjustment for age and liver enzyme activities: p = 0.012); with higher BMI, the risk increases significantly in males, whereas for females, the risk tends to decrease. In the group of overweight in-patients, we found higher readmission rates in males relative to females with an odds ratio of 1.8 (p = 0.038). No such significant effects were found in the other cohorts. This study's findings support previous results, suggesting that the easily accessible BMI may serve as a predictive and sex-sensitive biomarker for outcome in in-patients with AUD. Future studies are necessary to elucidate the underlying aetiopathological mechanisms.

Meta-analytic evidence for a sex-diverging association between alcohol use and body mass index

Alcohol use is an important health issue and has been suggested to contribute to the burden produced by obesity. Both alcohol use and obesity are subject to sex differences. The available studies on the relationship between alcohol use and body mass index (BMI) report inconsistent results with positive, negative, and null findings which requests a meta-analytic approach. Therefore, we conducted a meta-analysis of case-control, cohort, and cross-sectional studies. The systematic literature search and data extraction was performed by 3 independent raters. We conducted sex-separated meta-analyses and -regressions to investigate how alcohol consumption associates with BMI. Our systematic literature search resulted in 36 studies with 48 data sets (Nmen = 172,254; kmen = 30; Nwomen = 24,164; kwomen = 18; Nunknown sex = 672,344; kunknown sex = 24). Alcohol use was associated with higher BMI in men (g = 0.08 [0.07; 0.09]) and lower BMI in women (g = - 0.26 [- 0.29; - 0.22]). Moreover, we found the amount of daily alcohol intake in men (β = 0.001 [0.0008; 0.0014]) and ethnicity in women (g[Caucasians] = - 0.45 versus g[Asians] = - 0.05; z = 11.5, p < 0.0001) to moderate these effects. We here identified sex-diverging relationships between alcohol use and BMI, found daily alcohol intake and ethnicity to sex-specifically moderate these effects, and argue that sex-specific choice of beverage type and higher amount of daily alcohol use in men than in women account for these observations. Future research is needed to provide empirical evidence for the underlying mechanisms.

Sign-tracking modulates reward-related neural activation to reward cues, but not reward feedback

Research shows cognitive and neurobiological overlap between sign-tracking [value-modulated attentional capture (VMAC) by response-irrelevant, discrete cues] and maladaptive behaviour (e.g. substance abuse). We investigated the neural correlates of sign-tracking in 20 adults using an additional singleton task (AST) and functional magnetic resonance imaging (fMRI). Participants responded to a target to win monetary reward, the amount of which was signalled by singleton type (reward cue: high value vs. low value). Singleton responses resulted in monetary deductions. Sign-tracking-greater distraction by high-value vs. low-value singletons (H > L)-was observed, with high-value singletons producing slower responses to the target than low-value singletons. Controlling for age and sex, analyses revealed no differential brain activity across H > L singletons. Including sign-tracking as a regressor of interest revealed increased activity (H > L singletons) in cortico-subcortical loops, regions associated with Pavlovian conditioning, reward processing, attention shifts and relative value coding. Further analyses investigated responses to reward feedback (H > L). Controlling for age and sex, increased activity (H > L reward feedback) was found in regions associated with reward anticipation, attentional control, success monitoring and emotion regulation. Including sign-tracking as a regressor of interest revealed increased activity in the temporal pole, a region related to value discrimination. Results suggest sign-tracking is associated with activation of the 'attention and salience network' in response to reward cues but not reward feedback, suggesting parcellation between the two at the level of the brain. Results add to the literature showing considerable overlap in neural systems implicated in reward processing, learning, habit formation, emotion regulation and substance craving.

Gut-brain mechanisms underlying changes in disordered eating behaviour after bariatric surgery: a review

Bariatric surgery results in long-term weight loss and an improved metabolic phenotype due to changes in the gut-brain axis regulating appetite and glycaemia. Neuroendocrine alterations associated with bariatric surgery may also influence hedonic aspects of eating by inducing changes in taste preferences and central reward reactivity towards palatable food. However, the impact of bariatric surgery on disordered eating behaviours (e.g.: binge eating, loss-of-control eating, emotional eating and 'addictive eating'), which are commonly present in people with obesity are not well understood. Increasing evidence suggests gut-derived signals, such as appetitive hormones, bile acid profiles, microbiota concentrations and associated neuromodulatory metabolites, can influence pathways in the brain implicated in food intake, including brain areas involved in sensorimotor, reward-motivational, emotional-arousal and executive control components of food intake. As disordered eating prevalence is a key mediator of weight-loss success and patient well-being after bariatric surgery, understanding how changes in the gut-brain axis contribute to disordered eating incidence and severity after bariatric surgery is crucial to better improve treatment outcomes in people with obesity.

A Systematic Review on Common and Distinct Neural Correlates of Risk-taking in Substance-related and Non-substance Related Addictions

Both substance-related as well as non-substance-related addictions may include recurrent engagement in risky actions despite adverse outcomes. We here apply a unified approach and review task-based neuroimaging studies on substance-related (SRAs) and non-substance related addictions (NSRAs) to examine commonalities and differences in neural correlates of risk-taking in these two addiction types. To this end, we conducted a systematic review adhering to the PRISMA guidelines. Two databases were searched with predefined search terms to identify neuroimaging studies on risk-taking tasks in individuals with addiction disorders. In total, 19 studies on SRAs (comprising a total of 648 individuals with SRAs) and 10 studies on NSRAs (comprising a total of 187 individuals with NSRAs) were included. Risk-related brain activation in SRAs and NSRAs was summarized individually and subsequently compared to each other. Results suggest convergent altered risk-related neural processes, including hyperactivity in the OFC and the striatum. As characteristic for both addiction types, these brain regions may represent an underlying mechanism of suboptimal decision-making. In contrast, decreased DLPFC activity may be specific to SRAs and decreased IFG activity could only be identified for NSRAs. The precuneus and posterior cingulate show elevated activity in SRAs, while findings regarding these areas were mixed in NSRAs. Additional scarce evidence suggests decreased ventral ACC activity and increased dorsal ACC activity in both addiction types. Associations between identified activation patterns with drug use severity underpin the clinical relevance of these findings. However, this exploratory evidence should be interpreted with caution and should be regarded as preliminary. Future research is needed to evaluate the findings gathered by this review.

Task-Dependent Effective Connectivity of the Reward Network During Food Cue-Reactivity: A Dynamic Causal Modeling Investigation

Neural reactivity to food cues may play a central role in overeating and excess weight gain. Functional magnetic resonance imaging (fMRI) studies have implicated regions of the reward network in dysfunctional food cue-reactivity, but neural interactions underlying observed patterns of signal change remain poorly understood. Fifty overweight and obese participants with self-reported cue-induced food craving viewed food and neutral cues during fMRI scanning. Regions of the reward network with significantly greater food versus neutral cue-reactivity were used to specify plausible models of task-related neural interactions underlying the observed blood oxygenation level-dependent (BOLD) signal, and a bi-hemispheric winning model was identified in a dynamic causal modeling (DCM) framework. Neuro-behavioral correlations are investigated with group factor analysis (GFA) and Pearson's correlation tests. The ventral tegmental area (VTA), amygdalae, and orbitofrontal cortices (OFC) showed significant food cue-reactivity. DCM suggests these activations are produced by largely reciprocal dynamic signaling between these regions, with food cues causing regional disinhibition and an apparent shifting of activity to the right amygdala. Intrinsic self-inhibition in the VTA and right amygdala is negatively correlated with measures of food craving and hunger and right-amygdalar disinhibition by food cues is associated with the intensity of cue-induced food craving, but no robust cross-unit latent factors were identified between the neural group and behavioral or demographic variable groups. Our results suggest a rich array of dynamic signals drive reward network cue-reactivity, with the amygdalae mediating much of the dynamic signaling between the VTA and OFCs. Neuro-behavioral correlations suggest particularly crucial roles for the VTA, right amygdala, and the right OFC-amygdala connection but the more robust GFA identified no cross-unit factors, so these correlations should be interpreted with caution. This investigation provides novel insights into dynamic circuit mechanisms with etiologic relevance to obesity, suggesting pathways in biomarker development and intervention.

Using event-related potentials to study food-related cognition: An overview of methods and perspectives for future research

Electroencephalography (EEG), and the measure of event-related potentials (ERPs) in particular, are useful methods to study the cognitive and cerebral mechanisms underlying the perception and processing of food cues. Further research on these aspects is necessary to better understand how cognitive functioning may influence food choices in different populations (e.g. obese individuals, individuals with eating disorders). To help researchers in designing future studies, this article provides an overview of the methods used in the current literature on ERPs and food-related cognition. Several methodological aspects are explored to outline interesting perspectives for future research, including discussions on the main experimental tasks used, the cognitive functions assessed (e.g. inhibitory control, attentional processing), the characteristics of the participants recruited (e.g. weight status, eating behaviors), and the stimuli selected (e.g. food pictures, odors). The issues generated by some of these methodological choices are discussed, and a few guidelines are provided.

Integrative Hedonic and Homeostatic Food Intake Regulation by the Central Nervous System: Insights from Neuroimaging

Food intake regulation in humans is a complex process controlled by the dynamic interaction of homeostatic and hedonic systems. Homeostatic regulation is controlled by appetitive signals from the gut, adipose tissue, and the vagus nerve, while conscious and unconscious reward processes orchestrate hedonic regulation. On the one hand, sight, smell, taste, and texture perception deliver potent food-related feedback to the central nervous system (CNS) and influence brain areas related to food reward. On the other hand, macronutrient composition stimulates the release of appetite signals from the gut, which are translated in the CNS into unconscious reward processes. This multi-level regulation process of food intake shapes and regulates human ingestive behavior. Identifying the interface between hormones, neurotransmitters, and brain areas is critical to advance our understanding of conditions like obesity and develop better therapeutical interventions. Neuroimaging studies allow us to take a glance into the central nervous system (CNS) while these processes take place. This review focuses on the available neuroimaging evidence to describe this interaction between the homeostatic and hedonic components in human food intake regulation.

The role of sex in the association between cannabis use and working memory-related brain activity

Although cannabis use patterns differ between men and women, studies on sex differences on the effects of cannabis on the brain and cognitive control are largely lacking. Working memory (WM) is a component of cognitive control believed to be involved in the development and maintenance of addiction. In this study, we evaluated the association between cannabis use and WM (load) related brain activity in a large sample, enabling us to assess sex effects in this association. The brain activity of 104 frequent cannabis users (63% men) and 85 controls (53% men) was recorded during an N‐back WM task. Behavioral results showed a significant interaction between WM load and group for both accuracy and reaction time, with cannabis users showing a relatively larger decrease in performance with increasing WM load. Cannabis users compared to controls showed a relatively smaller reduction in WM (load) related activity in the precuneus and posterior cingulate cortex at higher WM load. This WM (load) related activity was not associated with performance nor cannabis use and related problems. An exploratory analysis showed higher WM‐related activity in the superior frontal gyrus in men compared to women. While cannabis users showed higher WM (load) related activity in central nodes of the default mode network, this was not directly attributable to group specific worsening of performance under higher cognitive load. Further research is necessary to assess whether observed group differences increase with higher cognitive load, how group differences relate to measures of cannabis use, and how sex affects these group differences.

Substance use disorder and obesogenic eating: Does working memory training strengthen ability to abstain from unwanted behaviors? A systematic review

INTRODUCTION

Abstaining from unwanted behaviors requires a sufficient balance between the executive and impulsive cognitive systems. Working memory (WM) is a vital component of both systems, identified in a wide range of research as the central and dominant component of executive function. WM potentially modulates the desires, tendencies, and behaviors specific to and seen in individuals with substance use disorder (SUD) and obesogenic eating (OE). Compared to healthy populations, research has shown individuals with SUD, as well as those who display OE, to have some degree of executive dysfunction, and both conditions have far-reaching health care implications. Additionally, these deficits are associated with impulsive behavior. Research has proposed that impulsive and so-called reward-driven responses could be altered through cognitive therapy and that both SUD and OE could benefit from working memory training (WMT).

METHOD

In this narrative review, we systematically align extant empirical reasoning and evidence with these assumptions. Our main aim is to ascertain and summarize the value of WMT for the treatment of both SUD and food reward consummatory behaviors. As a means to include detailed narrative accounts of all papers of potential value, our thresholds for meaningful improvements in both WM and unwanted behaviors are broad.

RESULTS

The results from the eleven qualifying studies are as follows: Nine of ten studies show a significant positive training effect of WMT on one or more components of WM capacity; three of six eligible papers (two on alcohol and one on opioid addiction) deliver notable improvements in SUD in response to WMT. One of two suitable studies showed WMT to be a moderately efficacious form of therapy for OE. Conversely, WMT appears to have negligible therapeutic benefit for cognitive function deficits or psychopathology unrelated to WM, suggesting that WMT has unique treatment efficacy for impulsive human behaviors.

CONCLUSION

In conclusion, more rigorous and uniform studies on WMT and impulsive harmful behaviors are required to give proof of the benefits of this potential useful treatment.

Brain response to food odors is not associated with body mass index and obesity-related metabolic health measures

Smell perception plays a role in eating behavior and might be involved in the development of obesity. In fact, olfactory function is impaired in obesity and might depend on metabolic health factors. To date, the underlying neural mechanisms remain unclear. Here, we investigate neural processing of food-related odors in normal-weight, overweight and obese individuals. Fifty-three young and healthy participants (28.8 ± 4.4 years, 27 female; 24 normal-weight, 10 overweight, and 19 obese) were presented with high- (chocolate, potato chips) and low-caloric (orange, cucumber) food odors during a functional magnetic resonance imaging (fMRI). We also assessed olfactory identification ability, body mass index (BMI), body fat percentage, insulin resistance, and leptin levels. In brief, olfactory perception of food odors was linked to brain activity in the entorhinal and piriform cortex, and the insula, hippocampus, and amygdala. Insulin resistance was negatively related to olfactory identification. Additionally, perception of sweet versus savory odors was related to a higher brain activity in the right middle/superior frontal gyrus. Finally, we found no effect of obesity status, BMI, metabolic factors, or body fat percentage on neural responses to food odors. Overall, this suggests that food odor processing might depend on factors other than body weight status or associated markers of metabolic health.

Food Addiction and Its Relationship to Weight- and Addiction-Related Psychological Parameters in Individuals With Overweight and Obesity

Background and Aims: It is assumed that a relevant subgroup of individuals experiences an addiction-like eating behaviour (Food Addiction), characterized by an impaired control over eating behaviour, emotional eating and food craving. Individuals experiencing Food Addiction partially share common symptomatology with Binge-Eating-Disorder and Bulimia Nervosa. The aim of this study was to investigate the prevalence of Food Addiction, general psychopathology, and associations with weight- and addiction-related constructs in individuals with overweight and obesity, who did not suffer from Binge-Eating-Disorder or Bulimia Nervosa.

Methods:N=213 (67.1% female; M_BMI=33.35kg/m², SD_BMI=3.79kg/m²) participants who were included in a weight loss program (I-GENDO project) reported BMI and completed questionnaires before the start of the treatment. Food Addiction severity, depressive symptoms, alcohol use disorder, internet use disorder, psychological distress, impulsivity personality trait, impulsive and emotional eating behaviour, food related inhibitory control, weight bias internalization, and self-efficacy were assessed.

Results: The prevalence of Food Addiction was 15% with higher, although not statistically significant, prevalence in female (18.2%) compared to male (8.6%) participants. Food Addiction was associated with higher BMI at baseline assessment, low self-esteem, impulsive and emotional eating behaviour, weight bias internalization, and deficits in food-related inhibitory control. In addition, correlations were found between Food Addiction and severity of depressive symptoms, internet use disorder, and psychological distress.

Conclusion: A relevant subgroup of participants experiences Food Addiction even when controlling for Binge-Eating-Disorder and Bulimia Nervosa. Future studies are warranted that investigate whether Food Addiction affects treatment success.

Neuroanatomical Correlates of Binge-Eating Behavior: At the Roots of Unstoppable Eating

Binge-eating refers to episodes of uncontrolled eating accompanied by a perceived loss of control, which can be common in the general population. Given the profound negative consequences of persistent binge-eating such as weight and eating disorders, it is vital to determine what makes someone more vulnerable than others to engage in such a conduct. A total of 42 normal-weight individuals (21 with binge-eating episodes and 21 without binge-eating episodes) underwent a structural magnetic resonance imaging measurement and Voxel-based morphometry (VBM) was used to assess between-group differences in terms of gray matter volume (GMV), together with self-report impulsivity and binge-eating measures. The results showed binge-eating individuals as characterized by higher trait impulsivity and greater regional GMV in the left middle frontal gyrus: however, the GMV in this region appeared to be positively correlated only with measures of binge-eating but not with trait impulsivity measures. These findings provide novel insights on the neurobiological roots of BE in normal-weight individuals and highlight how this behavior can be associated with brain morphometric changes within prefrontal regions also in a non-clinical population. Overall, this study provides a further characterization of the neural correlates of binge-eating and novel insights into the treatment of its more severe pathological forms.

Effects of bariatric surgery on functional connectivity of the reward and default mode network: A pre-registered analysis

Obesity imposes serious health risks and involves alterations in resting‐state functional connectivity of brain networks involved in eating behavior. Bariatric surgery is an effective treatment, but its effects on functional connectivity are still under debate. In this pre‐registered study, we aimed to determine the effects of bariatric surgery on major resting‐state brain networks (reward and default mode network) in a longitudinal controlled design. Thirty‐three bariatric surgery patients and 15 obese waiting‐list control patients underwent magnetic resonance imaging at baseline, after 6 and 12 months. We conducted a pre‐registered whole‐brain time‐by‐group interaction analysis, and a time‐by‐group interaction analysis on within‐network connectivity. In exploratory analyses, we investigated the effects of weight loss and head motion. Bariatric surgery compared to waiting did not significantly affect functional connectivity of the reward network and the default mode network (FWE‐corrected p > .05), neither whole‐brain nor within‐network. In exploratory analyses, surgery‐related BMI decrease (FWE‐corrected p = .041) and higher average head motion (FWE‐corrected p = .021) resulted in significantly stronger connectivity of the reward network with medial posterior frontal regions. This pre‐registered well‐controlled study did not support a strong effect of bariatric surgery, compared to waiting, on major resting‐state brain networks after 6 months. Exploratory analyses indicated that head motion might have confounded the effects. Data pooling and more rigorous control of within‐scanner head motion during data acquisition are needed to substantiate effects of bariatric surgery on brain organization.

Neural networks during delay discounting as trans-disease marker: A meta-analytical review

Delay discounting reflects a devaluation of delayed long-term benefits but pursuing immediate rewards. Higher discounting rates (h-DR) are found ubiquitous in many diseases and unhealthy conditions, particularly in addiction disorder (AD), attention-deficit/hyperactivity disorder (ADHD), and obesity. Thus, h-DR was considered to be a common benchmark across many diseases facilitating to understand one disease to relevant others, which was called trans-disease process. However, the common and specific neural biomarkers associated with this process has not yet been studied well. We performed a voxel-wise task-related neuroimaging meta-analysis to clarify the neural pattern of trans-disease process across AD, ADHD and obesity. We recruited 19 eligible papers, including 9 AD papers (154 patients), 6 ADHD papers (106 patients) and 4 obesity studies (94 patients). Neuroimaging meta-analysis demonstrated the presence of neural biomarkers of trans-disease process: these patients showed inadequate brain response in caudate, ventromedial and dorsolateral prefrontal cortex (dlPFC) than do of healthy controls (HCs). Disease-specific neural patterns were also found, with prominent hypoactivation in parahippocampal-striatum network for AD, hyperactivation in dopamine-projection striatum network for ADHD and decreased activity in dorsal anterior cingulate cortex and dlPFC for obesity. This study provided robust evidence to reveal the neural substrates of trans-disease process, as well further promoted the triple brain network model in favor of the theoretical developments of these neuropsychiatric disorders.

Linking categorical models for prediction of pleasantness score using individual predictions of sweetness and creaminess: An advancement of categorical modeling

The aim of this work was to develop and evaluate approaches of linked categorical models using individual predictions of probability. A model was developed using data from a study which assessed the perception of sweetness, creaminess, and pleasantness in dairy solutions containing variable concentrations of sugar and fat. Ordered categorical models were used to predict the individual sweetness and creaminess scores and these individual predictions were used as covariates in the model of pleasantness response. The model using individual predictions was compared to a previously developed model using the amount of fat and sugar as covariates driving pleasantness score. The model using the individual prediction of odds of sweetness and creaminess had a lower variability of pleasantness than the model using the content of sugar and fat in the test solutions, which indicates that the individual odds explain part of the variability in pleasantness. Additionally, simultaneous and sequential modeling approaches were compared for the linked categorical model. Parameter estimation was similar, but precision was better with sequential modeling approaches compared to the simultaneous modeling approach. The previous model characterizing the pleasantness response was improved by using individual predictions of sweetness and creaminess rather than the amount of fat and sugar in the solution. The application of this approach provides an advancement within categorical modeling showing how categorical models can be linked to enable the utilization of individual prediction. This approach is aligned with biology of taste sensory which is reflective of the individual perception of sweetness and creaminess, rather than the amount of fat and sugar in the solution.

Neural activation to loss and reward among alcohol naive adolescents who later initiate alcohol use

Adolescent alcohol use is associated with adverse psychosocial outcomes, including an increased risk of alcohol use disorder in adulthood. It is therefore important to identify risk factors of alcohol initiation in adolescence. Research to date has shown that altered neural activation to reward is associated with alcohol use in adolescence; however, few studies have focused on neural activation to loss and alcohol use. The current study examined neural activation to loss and reward among 64 alcohol naive 12−14 year olds that did (n = 20) and did not initiate alcohol use by a three year follow-up period. Results showed that compared to adolescents that did not initiate alcohol use, adolescents that did initiate alcohol use by the three year follow-up period had increased activation to loss in the left striatum (i.e., putamen), right precuneus, and the brainstem/pons when they were alcohol naive at baseline. By contrast, alcohol initiation was not associated with neural activation to winning a reward. These results suggest that increased activation in brain regions implicated in salience, error detection/self-referential processing, and sensorimotor function, especially to negative outcomes, may represent an initial vulnerability factor for alcohol use in adolescence.

Prevalence of food addiction in children and adolescents: A systematic review and meta-analysis

Food addiction (FA) has been as a construct that is associated with childhood obesity. However, relatively little is known regarding the prevalence of FA among children and adolescents. An instrument designed to assess FA among youth, the Yale Food Addiction Scale for Children and Adolescents (YFAS-C), has been developed and used to estimate FA prevalence among pediatric populations. The present systematic review and meta-analysis aimed to synthesize the results of FA prevalence among youth. Using keywords related to FA and children to search PubMed, Embase, Scopus, and Web of Science, we identified and analyzed 22 cross-sectional studies. No longitudinal studies were identified in the search. Meta-analysis with Freeman-Tukey Double Arcsine transformation was conducted to estimate FA prevalence. Meta-regression was applied to understand whether weight status (i.e., data from community samples vs. overweight/obese samples) is associated with FA. Eligible studies (N = 22) were analyzed using 6,996 participants. The estimated FA prevalence was 15% (95% CI 11-19%) for all samples, 12% (95% CI 8-17%) for community samples, and 19% (95% CI 14-26%) for overweight/obese samples. Meta-regression indicated that weight status was associated with FA severity (p = 0.002) and marginally with FA prevalence (p = 0.056). Healthcare providers should consider and address the high FA prevalence among pediatric population.

The Effect of Food Composition and Behavior on Neurobiological Response to Food: a Review of Recent Research

PURPOSE OF REVIEW

Controversy surrounds the construct of food addiction. The current review examines neurobiological evidence for the existence of food addiction as a valid diagnosis.

RECENT FINDINGS

Recent neuroimaging studies suggest significant overlap in the areas of the brain that are activated in relation to both food and drug addiction. Specifically, areas of the brain implicated in executive functioning (e.g., attention, planning, decision-making, inhibition), pleasure and the experience of reward, and sensory input and motor functioning display increased activation among individuals with symptoms of both food and drug addiction. Proposed symptoms of food addiction mirror those comprising other substance use disorder diagnoses, with similar psychological and behavioral sequelae. Results of neuroimaging studies suggest significant overlap in the areas of the brain that are activated in relation to both food and drug addiction, providing support for continued research into the construct of food addiction.

Legend of Weight Loss: a Crosstalk Between the Bariatric Surgery and the Brain

In recent years, plenty of researches have reported in obese individuals with abnormal brain processes implicated in homeostatic regulation, reward, emotion, memory, attention, and executive function in eating behaviors. Thus, treating obesity cannot remain "brainless." Behavioral and psychological interventions activate the food reward, attention, and motivation system, leading to minimal weight loss and high relapse rates. Pharmacotherapy is an effective weight loss method and regulate brain activity but with concerns about its brain function safety problems. Obesity surgery, the most effective therapy currently available for obesity, shows pronounced effects on brain activity, such as deactivation of reward and attention system, and activation of inhibition control toward food cues. In this review, we present an overview of alterations in the brain after the three common weight loss methods.

A neuroimaging investigation into the role of peripheral metabolic biomarkers in the anticipation of reward in alcohol use

BACKGROUND

The relationship between alcohol use and metabolism has focused on the effects of alcohol use on metabolic factors. Metabolic factors, such as triglycerides, cholesterol, and glucose, have been shown to be associated with increased risk for heavy alcohol consumption and alcohol use disorder (AUD). It's been suggested that changes in metabolic factors may play a role in reward seeking behaviors and pathways. Studies on feeding behavior and obesity revealed the role of triglycerides in neural response to food cues in neurocircuitry regulating reward and feeding behaviors. This study aimed to explore the relationship of peripheral metabolism, alcohol use, and reward processing in individuals that use alcohol.

METHODS

Ninety participants from a previously collected dataset were included in the analysis. Participants were treatment seeking, detoxified individuals with AUD and healthy individuals without AUD, with the following metabolic biomarkers: triglyceride, glucose, high- and low-density cholesterol, and HbA1c levels. Participants completed a neuroimaging version of the Monetary Incentive Delay task (MID).

RESULTS

Correlations on peripheral metabolic biomarkers, alcohol use, and neural activity during reward anticipation and outcome during the MID task were not significant. Mediation models revealed triglycerides and high-density cholesterol had significant effects on left anterior insula during anticipation of potential monetary loss and this effect was not mediated by alcohol use.

CONCLUSION

Limbic recruitment by anticipation of monetary rewards revealed an independent relationship with peripheral metabolism and was not affected by individual differences in alcohol use, despite the effects of alcohol use on metabolic markers and reward processing neural circuitry.

A meta-analytic investigation of the role of reward on inhibitory control

Contemporary theories predict that inhibitory control (IC) can be improved when rewards are available for successfully inhibiting. In non-clinical samples empirical research has demonstrated some support; however, "null" findings have also been published. The aim of this meta-analysis was to clarify the magnitude of the effect of reward on IC and identify potential moderators. A total of 73 articles (contributing k = 80 studies) were identified from PubMed, PsycInfo, and Scopus, published between 1997 and 2020, using a systematic search strategy. A random effects meta-analysis was performed on effect sizes generated from IC tasks, which included rewarded and non-rewarded inhibition trials. Moderator analyses were conducted on clinical samples (vs "healthy controls"), task type (go/no-go vs stop signal vs Flanker vs Simon vs Stroop vs Anti-saccade), reward type (monetary vs points vs other), and age (adults vs children). The prospect of reward for successful inhibition significantly improved IC (SMD = 0.429, 95% CI = 0.288, 0.570, I² = 96.7%) compared with no reward conditions/groups. This finding was robust against influential cases and outliers. The significant effect was present across all IC tasks. There was no evidence of the effect moderated by type of reward, age, or clinical samples. Moderator analyses did not resolve the considerable heterogeneity. The findings suggest that IC is a transient state that fluctuates in response to motivations driven by reward. Future research might examine the potential of improving IC through rewards as a behavioural intervention.

Basal ganglia lateralization in different types of reward

Reward processing is a fundamental human activity. The basal ganglia are recognized for their role in reward processes; however, specific roles of the different nuclei (e.g., nucleus accumbens, caudate, putamen and globus pallidus) remain unclear. Using quantitative meta-analyses we assessed whole-brain and basal ganglia specific contributions to money, erotic, and food reward processing. We analyzed data from 190 fMRI studies which reported stereotaxic coordinates of whole-brain, within-group results from healthy adult participants. Results showed concordance in overlapping and distinct cortical and sub-cortical brain regions as a function of reward type. Common to all reward types was concordance in basal ganglia nuclei, with distinct differences in hemispheric dominance and spatial extent in response to the different reward types. Food reward processing favored the right hemisphere; erotic rewards favored the right lateral globus pallidus and left caudate body. Money rewards engaged the basal ganglia bilaterally including its most anterior part, nucleus accumbens. We conclude by proposing a model of common reward processing in the basal ganglia and separate models for money, erotic, and food rewards.

Structural validity, measurement invariance, reliability and diagnostic accuracy of the Italian version of the Yale Food Addiction Scale 2.0 in patients with severe obesity and the general population

PURPOSE

To examine the structural validity, measurement invariance, reliability, and some other psychometrical properties of the Italian version of the Yale Food Addiction Scale 2 (I-YFAS 2.0) in patients with severe obesity and the general population.

METHODS

704 participants-400 inpatients with severe obesity and 304 participants enrolled from the general population-completed the I-YFAS 2.0 and questionnaires measuring eating disorder symptoms. A first confirmatory factor analysis (CFA) tested a hierarchical structure in which each item of the I-YFAS 2.0 loaded onto one of the twelve latent symptoms/criteria which loaded onto a general dimension of Food Addiction (FA). The second CFA tested a first-order structure in which symptoms/criteria of FA simply loaded onto a latent dimension. Measurement invariance (MI) between the group of inpatients with severe obesity and the sample from the general population was also tested. Finally, convergent validity, test-retest reliability, internal consistency, and prevalence analyses were performed.

RESULTS

CFAs confirmed the structure for the I-YFAS 2.0 for both the hierarchical structure and the first-order structure. Configural MI and strong MI were reached for hierarchical and the first-order structure, respectively. Internal consistencies were shown to be acceptable. Prevalence of FA was 24% in the group of inpatients with severe obesity and 3.6% in the sample from the general population.

CONCLUSIONS

The I-YFAS 2.0 represents a valid and reliable questionnaire for the assessment of FA in both Italian adult inpatients with severe obesity and the general population, and is a psychometrically sound tool for clinical as well as research purposes.

LEVEL OF EVIDENCE

Level V, descriptive study.

Reliance on model-based and model-free control in obesity

Consuming more energy than is expended may reflect a failure of control over eating behaviour in obesity. Behavioural control arises from a balance between two dissociable strategies of reinforcement learning: model-free and model-based. We hypothesized that weight status relates to an imbalance in reliance on model-based and model-free control, and that it may do so in a linear or quadratic manner. To test this, 90 healthy participants in a wide BMI range [normal-weight (n = 31), overweight (n = 29), obese (n = 30)] performed a sequential decision-making task. The primary analysis indicated that obese participants relied less on model-based control than overweight and normal-weight participants, with no difference between overweight and normal-weight participants. In line, secondary continuous analyses revealed a negative linear, but not quadratic, relationship between BMI and model-based control. Computational modelling of choice behaviour suggested that a mixture of both strategies was shifted towards less model-based control in obese participants. Our findings suggest that obesity may indeed be related to an imbalance in behavioural control as expressed in a phenotype of less model-based control potentially resulting from enhanced reliance on model-free computations.

Preliminary evidence for an association between intake of high-fat high-sugar diet, variations in peripheral dopamine precursor availability and dopamine-dependent cognition in humans

Obesity is associated with alterations in dopaminergic transmission and cognitive function. Rodent studies suggest that diets rich in saturated fat and refined sugars (HFS), as opposed to diets diets low in saturated fat and refined sugars (LFS), change the dopamine system independent of excessive body weight. However, the impact of HFS on the human brain has not been investigated. Here, we compared the effect of dietary dopamine depletion on dopamine-dependent cognitive task performance between two groups differing in habitual intake of dietary fat and sugar. Specifically, we used a double-blind within-subject cross-over design to compare the effect of acute phenylalanine/tyrosine depletion on a reinforcement learning and a working memory task, in two groups that are on opposite ends of the spectrum of self-reported HFS intake (low vs high intake: LFS vs HFS group). We tested 31 healthy young women matched for body mass index (mostly normal weight to overweight) and IQ. Depletion of peripheral precursors of dopamine reduced the working memory specific performance on the operation span task in the LFS, but not in the HFS group (P = 0.016). Learning from positive- and negative-reinforcement (probabilistic selection task) was increased in both diet groups after dopamine depletion (P = 0.049). As a secondary exploratory research question, we measured peripheral dopamine precursor availability (pDAP) at baseline as an estimate for central dopamine levels. The HFS group had a significantly higher pDAP at baseline compared to the LFS group (P = 0.025). Our data provide the first evidence indicating that the intake of HFS is associated with changes in dopamine precursor availability, which is suggestive of changes in central dopamine levels in humans. The observed associations are present in a sample of normal to overweight participants (ie, in the absence of obesity), suggesting that the consumption of a HFS might already be associated with altered behaviours. Alternatively, the effects of HFS diet and obesity might be independent.

Hierarchical integrated processing of reward-related regions in obese males: A graph-theoretical-based study

Abnormal activities in reward-related regions are associated with overeating or obesity. Preliminary studies have shown that changes in neural activity in obesity include not only regional reward regions abnormalities but also impairments in the communication between reward-related regions and multiple functional areas. A recent study has shown that the transitions between different neural networks are nonrandom and hierarchical, and that activation of particular brain networks is more likely to occur after other brain networks. The aims of this study were to investigate the key nodes of reward-related regions in obese males and explore the hierarchical integrated processing of key nodes. Twenty-four obese males and 24 normal-weight male controls of similar ages were recruited. The fMRI data were acquired using 3.0 T MRI. The fMRI data preprocessing was performed in DPABI and SPM 12. Degree centrality analyses were conducted using GRETNA toolkit, and Granger causality analyses were calculated using DynamicBC toolbox. Decreased degree centrality was observed in left ventral medial prefrontal cortex (vmPFC) and right parahippocampal/hippocampal gyrus in group with obesity. The group with obesity demonstrated increased effective connectivity between left vmPFC and several regions (left inferior temporal gyrus, left supplementary motor area, right insular cortex, right postcentral gyrus, right paracentral lobule and bilateral fusiform gyrus). Increased effective connectivity was observed between right parahippocampal/hippocampal gyrus and left precentral/postcentral gyrus. Decreased effective connectivity was found between right parahippocampal/hippocampal gyrus and left inferior parietal lobule. This study identified the features of hierarchical interactions between the key reward nodes and multiple function networks. These findings may provide more evidence for the existing view of hierarchical organization in reward processing.

Sweet/Fat Preference Taste in Subjects Who are Lean, Obese and Very Obese

Purpose

This study assessed the perception of sweetness, creaminess, and pleasantness from a sweet/fat preference test in subjects who are lean (BMI: 19–25), obese (BMI: 30–33) or very obese (BMI: 34–40) using categorical modeling.

Methods

Subjects tasted 16 dairy solutions consisting of 0%, 3.5%, 11.3% and 37.5% fat and each containing 0%, 5%, 10%, or 20% sugar and rated them for sweetness, creaminess and pleasantness.

Results

A proportional odds model described the perception of sweetness using an Emax for the effect of sugar and a linear effect for fat. Perception of creaminess was dependent on the fat and sugar content and was described with proportional odds model with linear effects of sugar and fat. Perception of pleasantness increased with sugar and fat but decreased in solutions containing 37.5% fat. A differential odds model using an Emax model for fat and sugar with a negative interaction between them allowed the sugar content to be less than proportional and the fat content to be greater than proportional for pleasantness.

Conclusions

Application of modeling provided understanding of these complex interactions of sugar and fat on the perception of sweetness, creaminess, and pleasantness and provides a tool to investigate obesity and pharmacological intervention.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-020-02968-9.

Caudate Functional Connectivity Associated With Weight Change in Adolescents

Background

Childhood obesity has become a global epidemic and the etiology of maladaptive ingestive behavior in children warrants further research. Mounting evidence suggests that the caudate is associated with body weight gain and obesity in adults. In adolescents, however, how caudate-related neural networks are associated with body weight gain is unclear because their central nervous systems are still developing.

Objectives

The current longitudinal resting-state functional magnetic resonance imaging (rs-fMRI) study was conducted to investigate the hypothesis that caudate-related neural networks have a role in weight gain in adolescents.

Methods

The study included 20 healthy adolescents with a mean age of 17.5 ± 2.0 years and a mean body mass index of 20.6 ± 2.1 who underwent baseline rs-fMRI then follow-up rs-fMRI approximately 1 year later. Body mass index (BMI) was measured at both timepoints. Seed-based functional connectivity analysis was utilized to analyze caudate-related functional connectivity (FC) using the caudate as a seed. Associations between caudate-related FC and BMI at baseline were assessed, as were associations between change in BMI and caudate-related FC between baseline and follow-up.

Results

At baseline, greater caudate-lateral prefrontal cortex FC was correlated with lower BMI (family wise error-corrected p < 0.05). Compared to the baseline, increased FC in the caudate-lateral prefrontal cortex at follow up were negatively associated with increased BMI (p < 0.05).

Conclusion

Given that the lateral prefrontal cortex and caudate are associated with inhibitory control, the caudate-lateral prefrontal cortex FC may have a preventive effect on weight gain in adolescents. The results of the current study suggest that developing inhibitory control would lead to the prevention of childhood obesity.

The Obesity-Susceptibility Gene TMEM18 Promotes Adipogenesis through Activation of PPARG

TMEM18 is the strongest candidate for childhood obesity identified from GWASs, yet as for most GWAS-derived obesity-susceptibility genes, the functional mechanism remains elusive. We here investigate the relevance of TMEM18 for adipose tissue development and obesity. We demonstrate that adipocyte TMEM18 expression is downregulated in children with obesity. Functionally, downregulation of TMEM18 impairs adipocyte formation in zebrafish and in human preadipocytes, indicating that TMEM18 is important for adipocyte differentiation in vivo and in vitro. On the molecular level, TMEM18 activates PPARG, particularly upregulating PPARG1 promoter activity, and this activation is repressed by inflammatory stimuli. The relationship between TMEM18 and PPARG1 is also evident in adipocytes of children and is clinically associated with obesity and adipocyte hypertrophy, inflammation, and insulin resistance. Our findings indicate a role of TMEM18 as an upstream regulator of PPARG signaling driving healthy adipogenesis, which is dysregulated with adipose tissue dysfunction and obesity.

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.

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.