Neural correlates of taste reward value across eating disorders

Neuroimaging studies of resting-state functional magnetic resonance imaging in eating disorders

Eating disorders (EDs), including anorexia nervosa (AN), bulimia nervosa (BN), binge-eating disorder (BED), and pica, are psychobehavioral conditions characterized by abnormal eating behaviors and an excessive preoccupation with weight and body shape. This review examines changes in brain regions and functional connectivity in ED patients over the past decade (2013-2023) using resting-state functional magnetic resonance imaging (rs-fMRI). Key findings highlight alterations in brain networks such as the default mode network (DMN), central executive network (CEN), and emotion regulation network (ERN). In individuals with AN, there is reduced functional connectivity in areas associated with facial information processing and social cognition, alongside increased connectivity in regions linked to sensory stimulation, aesthetic judgment, and social anxiety. Conversely, BED patients show diminished connectivity in the dorsal anterior cingulate cortex within the salience network and increased connectivity in the posterior cingulate cortex and medial prefrontal cortex within the DMN. These findings suggest that rs-fMRI could serve as a valuable biomarker for assessing brain function and predicting treatment outcomes in EDs, paving the way for personalized therapeutic strategies.

Food Avoidance and Aversive Goal Value Computation in Anorexia Nervosa

Anorexia nervosa (AN) is associated with food restriction and significantly low body weight, but the neurobiology of food avoidance in AN is unknown. Animal research suggests that food avoidance can be triggered by conditioned fear that engages the anterior cingulate and nucleus accumbens. We hypothesized that the neural activation during food avoidance in AN could be modeled based on aversive goal value processing. Nineteen females with AN and thirty healthy controls matched for age underwent functional magnetic resonance brain imaging while conducting a food avoidance task. During active control free-bid and computer-generated forced-bid trials, participants bid money to avoid eating food items. Brain activation was parametrically modulated with the trial-by-trial placed bids. During free-bid trials, the AN group engaged the caudate nucleus, nucleus accumbens, ventral anterior cingulate, and inferior and medial orbitofrontal cortex more than the control group. High- versus low-bid trials in the AN group were associated with higher caudate nucleus response. Emotion dysregulation and intolerance of uncertainty scores were inversely associated with nucleus accumbens free-bid trial brain response in AN. This study supports the idea that food avoidance behavior in AN involves aversive goal value computation in the nucleus accumbens, caudate nucleus, anterior cingulate, and orbitofrontal cortex.

Neuronal activity and reward processing in relation to binge eating

PURPOSE OF REVIEW

Studies increasingly show the importance of reward processing in binge eating and provide evidence of associated changes in the neurobiological reward system. This review gives an up-to-date overview of the neurobiological substrates of reward processing subconstructs in binge eating. Neural findings are linked to different behavioral theories and the clinical relevance is discussed.

RECENT FINDINGS

Increased neural responses in the orbitofrontal cortex, anterior cingulate cortex as well as striatum during anticipation and receipt of food rewards are found in association to binge eating. Increased model-free learning is also found and associated with altered brain reward reactivity. Data in rest report reduced striatal dopamine release and lower frontostriatal connectivity. Mechanisms of onset of binge eating are less clear, but specific personality traits, related to frontostriatal dysconnectivity, probably increase the risk of binge eating onset.

SUMMARY

Both structural and task-based imaging studies show differences in the neurobiological reward system in binge eating. These changes are linked to specific reward processing, such as altered reward responsiveness to food cues, reinforcement learning, and habitual behavior. Findings are lined with different behavioral theories of binge eating, and a staging model is described, from onset to full illness development. Understanding the specific underlying aberrant reward mechanism in binge eating, associated with different stages of the illness, enables caregivers to focus their treatment more precisely.

Binge-Eating Precursors in Children and Adolescents: Neurodevelopment, and the Potential Contribution of Ultra-Processed Foods

Binge-eating disorder (BED) is a highly prevalent disorder. Subthreshold BED conditions (sBED) are even more frequent in youth, but their significance regarding BED etiology and long-term prognosis is unclear. A better understanding of brain findings associated with BED and sBED, in the context of critical periods for neurodevelopment, is relevant to answer such questions. The present narrative review starts from the knowledge of the development of emotional self-regulation in youth, and the brain circuits supporting emotion-regulation and eating behaviour. Next, neuroimaging studies with sBED and BED samples will be reviewed, and their brain-circuitry overlap will be examined. Deficits in inhibition control systems are observed to precede, and hyperactivity of reward regions to characterize, sBED, with overlapping findings in BED. The imbalance between reward/inhibition systems, and the implication of interoception/homeostatic processing brain systems should be further examined. Recent knowledge of the potential impact that the high consumption of ultra-processed foods in paediatric samples may have on these sBED/BED-associated brain systems is then discussed. There is a need to identify, early on, those sBED individuals at risk of developing BED at neurodevelopmental stages when there is a great possibility of prevention. However, more neuroimaging studies with sBED/BED pediatric samples are needed.

Food Restriction in Anorexia Nervosa in the Light of Modern Learning Theory: A Narrative Review

Improvements in the clinical management of anorexia nervosa (AN) are urgently needed. To do so, the search for innovative approaches continues at laboratory and clinical levels to translate new findings into more effective treatments. In this sense, modern learning theory provides a unifying framework that connects concepts, methodologies and data from preclinical and clinical research to inspire novel interventions in the field of psychopathology in general, and of disordered eating in particular. Indeed, learning is thought to be a crucial factor in the development/regulation of normal and pathological eating behaviour. Thus, the present review not only tries to provide a comprehensive overview of modern learning research in the field of AN, but also follows a transdiagnostic perspective to offer testable explanations for the origin and maintenance of pathological food rejection. This narrative review was informed by a systematic search of research papers in the electronic databases PsycInfo, Scopus and Web of Science following PRISMA methodology. By considering the number and type of associations (Pavlovian, goal-directed or habitual) and the affective nature of conditioning processes (appetitive versus aversive), this approach can explain many features of AN, including why some patients restrict food intake to the point of life-threatening starvation and others restrict calorie intake to lose weight and binge on a regular basis. Nonetheless, it is striking how little impact modern learning theory has had on the current AN research agenda and practice.

Anorexia nervosa as a disorder of the subcortical-cortical interoceptive-self

PURPOSE

Anorexia nervosa (AN) is characterized by a diminished capacity in perceiving the physiological correlates of interoceptive sensations, namely bodily self-consciousness. Given the neural division of self-processing into interoceptive-, exteroceptive- and mental-self, we hypothesize neural deficits in the interoceptive-processing regions in AN.

METHODS

To prove this, we reviewed resting state (rs), task and rest-task studies in AN literature.

RESULTS

Neuronal data demonstrate the following in AN: (i) decreased rs-functional connectivity (rsFC) of subcortical-cortical midline structures (SCMS); (ii) reduced rsFC between medial (default-mode network/DMN and salience network/SN) and lateral (executive-control network/ECN) cortical regions; (iii) decreased rsFC in mainly the regions of the interoceptive-self; (iv) altered activity with overall increased activity in response to sensory/body image stimuli, especially in the regions of the interoceptive-self; (v) lack of a clear task-related distinction between own's and others' body image.

CONCLUSION

These data may indicate that rs-hypoconnectivity between SCMS, as neural correlate of a reduced intero-exteroceptive integration resulting in self-objectification, might be linked to overall increased activity in interoceptive regions during sensory/body image stimuli in AN, engendering an "anxious bodily self."

LEVEL OF EVIDENCE

I: Systematic review.

The neurobiological reward system and binge eating: A critical systematic review of neuroimaging studies

OBJECTIVE

Changes in reward processing are hypothesized to play a role in the onset and maintenance of binge eating (BE). However, despite an increasing number of studies investigating the neurobiological reward system in individuals who binge eat, no comprehensive systematic review exists on this topic. Therefore, this review has the following objectives: (1) identify structural and functional changes in the brain reward system, either during rest or while performing a task; and (2) formulate directions for future research.

METHODS

A search was conducted of articles published until March 31, 2022. Neuroimaging studies were eligible if they wanted to study the reward system and included a group of individuals who binge eat together with a comparator group. Their results were summarized in a narrative synthesis.

RESULTS

A total of 58 articles were included. At rest, individuals who binge eat displayed a lower striatal dopamine release, a change in the volume of the striatum, frontal cortex, and insula, as well as a lower frontostriatal connectivity. While performing a task, there was a higher activity of the brain reward system when anticipating or receiving food, more model-free reinforcement learning, and more habitual behavior. Most studies only included one patient group, used general reward-related measures, and did not evaluate the impact of comorbidities, illness duration, race, or sex.

DISCUSSION

Confirming previous hypotheses, this review finds structural and functional changes in the neurobiological reward system in BE. Future studies should compare disorders, use measures that are specific to BE, and investigate the impact of confounding factors.

PUBLIC SIGNIFICANCE STATEMENT

This systematic review finds that individuals who binge eat display structural and functional changes in the brain reward system. These changes could be related to a higher sensitivity to food, relying more on previous experiences when making decisions, and more habitual behavior. Future studies should use a task that is specific to binge eating, look across different patient groups, and investigate the impact of comorbidities, illness duration, race, and sex.

Understanding relations between intolerance of uncertainty and body checking and body avoiding in anorexia nervosa

BACKGROUND

A key feature of anorexia nervosa is body image disturbances and is often expressed by dysfunctional body-related behaviours such as body checking and body avoiding. These behaviours are thought to contribute to both the maintenance and relapse of AN, yet empirical evidence is scarce. One variable that may contribute to the need for engaging in these behaviours is intolerance of uncertainty. This study aims to investigate body checking and body avoiding and its relations with intolerance of uncertainty in women with anorexia nervosa (AN-ill; 70), women recovered from AN (AN-rec; 85) and control group (127).

METHODS

Three questionnaires were completed, measuring eating pathology, intolerance of uncertainty and body checking and body avoiding. One-way ANOVAS were used to test group differences. Moderation analyses were used to investigate associations between variables.

RESULTS

Levels of intolerance of uncertainty, body checking and body avoiding were highest in AN-ill followed by AN-rec and, lastly, the control group, confirming group differences. Intolerance of uncertainty was associated with body checking in the AN-rec group and the control group but not in the AN-ill group. The association between intolerance of uncertainty and body avoiding was reported in the AN-rec group and only marginally in the control group.

CONCLUSION

Levels of intolerance of uncertainty, body checking and body avoiding were highest in AN-ill, however still elevated in AN-rec, confirming the presence of body image disturbances, even after recovery. The unique associations between intolerance of uncertainty and body checking and body avoiding within the studied groups may represent different stages of the illness. In the AN-rec group, the relation between intolerance of uncertainty, body checking and body avoiding may be driven by trait anxiety. For AN-ill group, body checking and body avoiding may eventually have grown into habitual patterns, rather than a strategy to ameliorate anxiety and uncertainty. Women with anorexia nervosa often experience disturbances in their body image and are expressed in body-related behaviours such as body checking and body avoiding. These behaviours are thought to contribute to both the maintenance and relapse of anorexia nervosa. Intolerance of uncertainty is defined as the incapacity to tolerate uncertainty and may contribute to the need for engaging in these behaviours. This study aims to investigate body checking and body avoiding and its relations with intolerance of uncertainty in women with anorexia nervosa (AN-ill; 70), women recovered from AN (AN-rec; 85) and control group (127). Three questionnaires were completed, measuring eating pathology, intolerance of uncertainty and body checking and body avoiding. Levels of intolerance of uncertainty, body checking and body avoiding were highest in AN-ill and still elevated in AN-rec, even after recovery. The associations between intolerance of uncertainty and body checking and body avoiding within the studied groups may represent different stages of the illness. In the AN-rec group, the relation between intolerance of uncertainty, body checking and body avoiding may be driven by trait anxiety. For AN-ill group, body checking and body avoiding may have grown into habitual patterns, rather than a strategy to ameliorate anxiety and uncertainty.

State or trait: the neurobiology of anorexia nervosa - contributions of a functional magnetic resonance imaging study

BACKGROUND

The understanding of the cerebral neurobiology of anorexia nervosa (AN) with respect to state- versus trait-related abnormalities is limited. There is evidence of restitution of structural brain alterations with clinical remission. However, with regard to functional brain abnormalities, this issue has not yet been clarified.

METHODS

We compared women with AN (n = 31), well-recovered female participants (REC) (n = 18) and non-patients (NP) (n = 27) cross-sectionally. Functional magnetic resonance imaging was performed to compare neural responses to food versus non-food images. Additionally, affective ratings were assessed.

RESULTS

Functional responses and affective ratings did not differ between REC and NP, even when applying lenient thresholds for the comparison of neural responses. Comparing REC and AN, the latter showed lower valence and higher arousal ratings for food stimuli, and neural responses differed with lenient thresholds in an occipital region.

CONCLUSIONS

The data are in line with some previous findings and suggest restitution of cerebral function with clinical recovery. Furthermore, affective ratings did not differ from NP. These results need to be verified in intra-individual longitudinal studies.

From Desire to Dread-A Neurocircuitry Based Model for Food Avoidance in Anorexia Nervosa

Anorexia nervosa is a severe psychiatric illness associated with food avoidance. Animal models from Berridge et al. over the past decade showed that environmental ambience, pleasant or fear inducing, can trigger either appetitive (desire) or avoidance (dread) behaviors in animals via frontal cortex, nucleus accumbens dopamine D1 and D2 receptors, and hypothalamus. Those mechanisms could be relevant for understanding anorexia nervosa. However, models that translate animal research to explain the psychopathology of anorexia nervosa are sparse. This article reviews animal and human research to find evidence for whether this model can explain food avoidance behaviors in anorexia nervosa. Research on anorexia nervosa suggests fear conditioning to food, activation of the corticostriatal brain circuitry, sensitization of ventral striatal dopamine response, and alterations in hypothalamic function. The results support the applicability of the animal neurocircuitry derived model and provide directions to further study the pathophysiology that underlies anorexia nervosa.

Moving towards specificity: A systematic review of cue features associated with reward and punishment in anorexia nervosa

Models of anorexia nervosa (AN) posit that symptoms are maintained through deficient reward and enhanced punishment processing. However, theoretical and empirical inconsistencies highlight the need for a more nuanced conceptualization of this literature. Our goal was to comprehensively review the research on reward and punishment responding in AN from a cue-specific lens to determine which stimuli evoke or discourage reward and punishment responses in this population, and, ultimately, what properties these rewarding and punishing cues might share. A systematic review interrogating reward and punishment responses to specific cues yielded articles (n = 92) that examined responses to disorder relevant (e.g., food) and irrelevant (e.g., money) stimuli across self-report, behavioral, and biological indices. Overall, in most studies individuals with AN exhibited aversive responses to cues signaling higher body weights, social contexts, and monetary losses, and appetitive responses to cues for weight loss behaviors and thinness. Findings were more mixed on responses to palatable food and monetary gains. Results highlight that reward and punishment responding in AN are context specific and may be affected by varied stimulus qualities (e.g., predictability, controllability, delay, effort). Increasing specificity in future research on reward and punishment mechanisms in AN will better inform development of precisely-targeted interventions.

Neuroimaging and eating disorders

PURPOSE OF REVIEW

Eating disorders are severe psychiatric disorders with a suspected complex biopsychosocial cause. The purpose of this review is to synthesize the recent literature on brain imaging in eating disorders.

RECENT FINDINGS

Food restriction as well as binge eating and purging behaviors are associated with lower regional brain volumes or cortical thickness, but those changes largely return to normal with normalization of weight and eating behavior. Computational modeling has started to identify patterns of structural and functional imaging data that classify eating disorder subtypes, which could be used in the future, diagnostically and to better understand disorder-specific psychopathology. The prediction error model, a computational approach to assess dopamine-related brain reward function, helped support a brain-based model for anorexia nervosa. In that model, the conscious motivation to restrict conflicts with body signals that stimulate eating. This conflict causes anxiety and drives a vicious cycle of food restriction.

SUMMARY

Novel brain research supports the notion that eating disorders have distinct neurobiological underpinnings. This new knowledge can be used to describe disease models to patients and develop novel treatments.

The promise of neurobiological research in anorexia nervosa

PURPOSE OF REVIEW

This article reviews new research in the context of existing literature to identify approaches that will advance understanding of the persistence of anorexia nervosa.

RECENT FINDINGS

Neuroscience research in anorexia nervosa has yielded disparate findings: no definitive neural mechanism underlying illness vulnerability or persistence has been identified and no clear neural target for intervention has emerged. Recent advances using structural and functional neuroimaging research, as well as new techniques for applying and combining these approaches, have led to a refined understanding of changes in neural architecture among individuals who are acutely ill, have undergone renourishment, or are in recovery/remission. In particular, advances have come from the incorporation of computational and translational approaches, as well as efforts to link experimental paradigms with illness-relevant behavior. Recent findings converge to suggest abnormalities in systems involved in reward learning and processing among individuals with anorexia nervosa.

SUMMARY

Anorexia nervosa is associated with neurobiological abnormalities. Aberrant learning and reward processing may contribute to the persistence of illness. To better utilize new techniques to understand the neural mechanisms of persistent anorexia nervosa, it may help to distinguish stages of illness and to link neurobiology with maladaptive behavior.

Examining weight suppression as a transdiagnostic factor influencing illness trajectory in bulimic eating disorders

Recent research indicates that weight suppression (WS: defined as the difference between highest lifetime and current weight) prospectively predicts illness trajectory across eating disorders characterized by binge eating, including AN binge-purge subtype (ANbp), bulimia nervosa (BN), and binge eating disorder (BED), collectively referred to as bulimic eating disorders. Through a series of studies, we have developed a model to explain the link between WS and illness trajectory in bulimic eating disorders. Our model posits that WS contributes to reduced circulating leptin, which leads to reduced postprandial glucagon-like peptide 1 (GLP-1) response. Diminished leptin and GLP-1 function contribute to alterations in two reward-related constructs in the Research Domain Criteria (RDoC): reward value/effort and reward satiation. Respectively, these changes increase drive/motivation to consume food and decrease ability for food consumption to lead to a state of satiation/satisfaction. Combined, these alterations increase risk for experiencing large, out-of-control binge-eating episodes. The following review presents evidence that contributed to the development of this model as well as preliminary findings from an on-going project funded to test this model.

Motivation to eat and not to eat - The psycho-biological conflict in anorexia nervosa

Anorexia nervosa is a severe psychiatric illness with high mortality. Brain imaging research has indicated altered reward circuits in the disorder. Here we propose a disease model for anorexia nervosa, supported by recent studies, that integrates psychological and biological factors. In that model, we propose that there is a conflict between the conscious motivation to restrict food, and a body-homeostasis driven motivation to approach food in response to weight loss. These opposing motivations trigger anxiety, which maintains the vicious cycle of ongoing energy restriction and weight loss.