New insights into symptoms and neurocircuit function of anorexia nervosa

Altered brain response to reward and punishment in adolescents with Anorexia nervosa

Adults recovered from Anorexia nervosa (AN) have altered reward modulation within striatal limbic regions associated with the emotional significance of stimuli, and executive regions concerned with planning and consequences. We hypothesized that adolescents with AN would show similar disturbed reward modulation within the striatum and the anterior cingulate cortex, a region connected to the striatum and involved in reward-guided action selection. Using functional magnetic resonance imaging, twenty-two adolescent females (10 restricting-type AN, 12 healthy volunteers) performed a monetary guessing task. Time series data associated with monetary wins and losses within striatal and cingulate regions of interest were subjected to a linear mixed effects analysis. All participants responded more strongly to wins versus losses in limbic and anterior executive striatal territories. However, AN participants exhibited an exaggerated response to losses compared to wins in posterior executive and sensorimotor striatal regions, suggesting altered function in circuitry responsible for coding the affective context of stimuli and action selection based upon these valuations. As AN individuals are particularly sensitive to criticism, failure, and making mistakes, these findings may reflect the neural processes responsible for a bias in those with AN to exaggerate negative consequences.

[Anorexia nervosa - from a neuroscience perspective]

Anorexia nervosa is a frequent disorder especially among adolescent girls and young women, with high morbidity, mortality, and relapse rates. To date, no single therapeutic approach has proved to be superior to others (Herpertz et al., 2011). It remains unclear how its etiology and pathology are encoded within cognitive, neural, and endocrinological processes that modulate important mechanisms in appetitive processing and weight regulation. Yet, several trait characteristics have been identified in AN which might reflect predisposing factors. Further, altered levels of neuropeptides and hormones that regulate appetite and feeding behavior have been found during both the acute and the recovered state, pointing to dysfunctional mechanisms in AN that persist even after malnutrition has ceased. Researchers are also hoping that brain imaging techniques will allow for a more detailed investigation of the neural basis of reward and punishment sensitivity that appears to be altered in AN. The integration and extension of recent findings in these areas will hopefully provide a more comprehensive understanding of the disorder and hence enable the development of more effective treatments.

Increased BOLD signal in the fusiform gyrus during implicit emotion processing in anorexia nervosa

Background

The behavioural literature in anorexia nervosa (AN) has suggested impairments in psychosocial functioning and studies using facial expression processing tasks (FEPT) have reported poorer recognition and slower identification of emotions.

Methods

Functional magnetic resonance imaging (fMRI) was used alongside a FEPT, depicting neutral, mildly happy and happy faces, to examine the neural correlates of implicit emotion processing in AN. Participants were instructed to specify the gender of the faces. Levels of depression, anxiety, obsessive–compulsive symptoms and eating disorder behaviour were obtained and principal component analysis (PCA) was performed to acquire uncorrelated variables.

Results

fMRI analysis revealed a greater blood-oxygenation level dependent (BOLD) response in AN in the right fusiform gyrus to all facial expressions. This response showed a linear increase with the happiness of the facial expression and was found to be stronger in those not taking medication. PCA analysis revealed a single component indicating a greater level of general clinical symptoms.

Conclusion

Neuroimaging findings would suggest that alterations in implicit emotion processing in AN occur during early perceptual processing of social signals and illustrate greater engagement on the FEPT. The lack of separate components using PCA suggests that the questionnaires used might not be suited as predictive measures.

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Greater BOLD response in AN in the right fusiform gyrus to all facial expressions.

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The BOLD response showed a linear increase with the happiness of the expression

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The BOLD response was stronger in those not taking psychotropic medication

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These alterations occur during early perceptual processing of social signals

Genetics of eating disorders

Disordered eating behavior is the core symptom of the complex disorders anorexia nervosa and bulimia nervosa. Twin and family studies derive high heritability estimates. Hence, substantial genetic influences on the etiology can be assumed for both. Initially, candidate gene studies pertaining to the monoaminergic neurotransmitter systems and to body weight regulation comprised the core of the genetic analyses. Unfortunately, confirmed, solid findings substantiated in meta-analyses are rare, so that eventually none of these associations is unequivocal. Thus, systematic, genome-wide approaches emerged to identify genes with no a priori evidence for their involvement in eating disorders. Genome-wide association studies have hinted to formerly unknown genetic regions. However, significant genome-wide findings have not yet been reported.

Greater anterior insula activation during anticipation of food images in women recovered from anorexia nervosa versus controls

Individuals with anorexia nervosa (AN) restrict food consumption and become severely emaciated. Eating food, even thinking of eating food, is often associated with heightened anxiety. However, food cue anticipation in AN is poorly understood. Fourteen women recovered from AN and 12 matched healthy control women performed an anticipation task viewing images of food and object images during functional magnetic resonance imaging. Comparing anticipation of food versus object images between control women and recovered AN groups showed significant interaction only in the right ventral anterior insula, with greater activation in recovered AN anticipating food images. These data support the hypothesis of a disconnect between anticipating and experiencing food stimuli in recovered AN. Insula activation positively correlated with pleasantness ratings of palatable foods in control women, while no such relationship existed in recovered AN, which is further evidence of altered interoceptive function. Finally, these findings raise the possibility that enhanced anterior insula anticipatory response to food cues in recovered AN could contribute to exaggerated sensitivity and anxiety related to food and eating.

Predictors of the resumption of menses in adolescent anorexia nervosa

BACKGROUND

The resumption of menses is an important indicator of recovery in anorexia nervosa (AN). Patients with early-onset AN are at particularly great risk of suffering from the long-term physical and psychological consequences of persistent gonadal dysfunction. However, the clinical variables that predict the recovery of menstrual function during weight gain in AN remain poorly understood. The aim of this study was to investigate the impact of several clinical parameters on the resumption of menses in first-onset adolescent AN in a large, well-characterized, homogenous sample that was followed-up for 12 months.

METHODS

A total of 172 female adolescent patients with first-onset AN according to DSM-IV criteria were recruited for inclusion in a randomized, multi-center, German clinical trial. Menstrual status and clinical variables (i.e., premorbid body mass index (BMI), age at onset, duration of illness, duration of hospital treatment, achievement of target weight at discharge, and BMI) were assessed at the time of admission to or discharge from hospital treatment and at a 12-month follow-up. Based on German reference data, we calculated the percentage of expected body weight (%EBW), BMI percentile, and BMI standard deviation score (BMI-SDS) for all time points to investigate the relationship between different weight measurements and resumption of menses.

RESULTS

Forty-seven percent of the patients spontaneously began menstruating during the follow-up period. %EBW at the 12-month follow-up was strongly correlated with the resumption of menses. The absence of menarche before admission, a higher premorbid BMI, discharge below target weight, and a longer duration of hospital treatment were the most relevant prognostic factors for continued amenorrhea.

CONCLUSIONS

The recovery of menstrual function in adolescent patients with AN should be a major treatment goal to prevent severe long-term physical and psychological sequelae. Patients with premenarchal onset of AN are at particular risk for protracted amenorrhea despite weight rehabilitation. Reaching and maintaining a target weight between the 15th and 20th BMI percentile is favorable for the resumption of menses within 12 months. Whether patients with a higher premorbid BMI may benefit from a higher target weight needs to be investigated in further studies.

Nutritional rehabilitation in anorexia nervosa: review of the literature and implications for treatment

Restoration of weight and nutritional status are key elements in the treatment of anorexia nervosa (AN). This review aims to describe issues related to the caloric requirements needed to gain and maintain weight for short and long-term recovery for AN inpatients and outpatients.We reviewed the literature in PubMed pertaining to nutritional restoration in AN between 1960-2012. Based on this search, several themes emerged: 1. AN eating behavior; 2. Weight restoration in AN; 3. Role of exercise and metabolism in resistance to weight gain; 3. Medical consequences of weight restoration; 4. Rate of weight gain; 5. Weight maintenance; and 6. Nutrient intake.A fair amount is known about overall caloric requirements for weight restoration and maintenance for AN. For example, starting at 30-40 kilocalories per kilogram per day (kcal/kg/day) with increases up to 70-100 kcal/kg/day can achieve a weight gain of 1-1.5 kg/week for inpatients. However, little is known about the effects of nutritional deficits on weight gain, or how to meet nutrient requirements for restoration of nutritional status.This review seeks to draw attention to the need for the development of a foundation of basic nutritional knowledge about AN so that future treatment can be evidenced-based.

Resistance to treatment and change in anorexia nervosa [corrected]: a clinical overview

BACKGROUND

Current literature on Eating Disorders (EDs) is devoid of evidence-based findings providing support to effective treatments, mostly for anorexia nervosa (AN). This lack of successful guidelines may play a role in making these disorders even more resistant. In fact, many individuals do not respond to the available treatments and develop an enduring and disabling illness. With this overview we aimed to highlight and discuss treatment resistance in AN--with an in-depth investigation of resistance-related psychological factors.A literature search was conducted on PubMed and PsychINFO; English-language articles published between 1990 and 2013 investigating the phenomenon of resistance to treatment in AN have been considered.

DISCUSSION

The selected papers have been then grouped into four main thematic areas: denial of illness; motivation to change; maintaining factors and treatment outcome; and therapeutic relationship. Eating symptomatology was found to only partially explain resistance to treatment. The role of duration of illness has been questioned whilst some maintaining factors seemed promising in providing a useful framework for this phenomenon. Emotive and relational aspects have been investigated on their role in resistance as well as therapists' countertransference.

SUMMARY

Remarkably there has been little research done on resistance to treatment in the ED field, in spite of its clinical relevance. Motivation, insight and subjective meaning of the illness can be useful tools to manage the resistance phenomenon when coupled with a wider approach. The latter enables the therapists to be aware of their role in the therapeutic alliance through countertransference aspects and to consider the EDs as disorders of the development of both personality and self, entailing severe impairments as regards identity and relationships.

Alterations in white matter microstructure in women recovered from anorexia nervosa

OBJECTIVE

A recent study of ill individuals with anorexia nervosa (AN) reported microstructural alterations in white matter integrity including lower fractional anisotropy and higher mean diffusivity. This study was designed to determine whether such alterations exist in long-term recovered AN individuals and to examine potential associations with underlying AN traits.

METHOD

Twelve adult women recovered from restricting-type AN and 10 control women were studied using diffusion tensor imaging.

RESULTS

Overall, there was no significant fractional anisotropy alteration in recovered AN, in contrast to a prior study reporting lower fractional anisotropy in ill AN. Further, recovered AN showed lower mean diffusivity in frontal, parietal and cingulum white matter relative to control women, contrary to elevated mean diffusivity previously reported in ill AN. Lower longitudinal diffusivity in recovered AN was associated with higher harm avoidance. However, more severe illness history was associated with worse white matter integrity after recovery in the same direction as reported in prior work.

DISCUSSION

Our findings suggest that fractional anisotropy in recovered AN is not different from controls, however, a novel pattern of lower mean diffusivity was evidenced in recovered AN, and this alteration was associated with harm avoidance. Notably, severity of illness history may have long-term consequences, emphasizing the importance of aggressive treatment.

Is deep brain stimulation a treatment option for anorexia nervosa?

Anorexia nervosa (AN) is a severe psychiatric disorder with high rates of morbidity, comorbidity and mortality, which in a subset of patients (21%) takes on a chronic course. Since an evidence based treatment for AN is scarce, it is crucial to investigate new treatment options, preferably focused on influencing the underlying neurobiological mechanisms of AN. The objective of the present paper was to review the evidence for possible neurobiological correlates of AN, and to hypothesize about potential targets for Deep brain stimulation (DBS) as a treatment for chronic, therapy-refractory AN. One avenue for exploring new treatment options based on the neurobiological correlates of AN, is the search for symptomatologic and neurobiologic parallels between AN and other compulsivity- or reward-related disorders. As in other compulsive disorders, the fronto-striatal circuitry, in particular the insula, the ventral striatum (VS) and the prefrontal, orbitofrontal, temporal, parietal and anterior cingulate cortices, are likely to be implicated in the neuropathogenesis of AN. In this paper we will review the few available cases in which DBS has been performed in patients with AN (either as primary diagnosis or as comorbid condition). Given the overlap in symptomatology and neurocircuitry between reward-related disorders such as obsessive compulsive disorder (OCD) and AN, and the established efficacy of accumbal DBS in OCD, we hypothesize that DBS of the nucleus accumbens (NAc) and other areas associated with reward, e.g. the anterior cingulated cortex (ACC), might be an effective treatment for patients with chronic, treatment refractory AN, providing not only weight restoration, but also significant and sustained improvement in AN core symptoms and associated comorbidities and complications. Possible targets for DBS in AN are the ACC, the ventral anterior limb of the capsula interna (vALIC) and the VS. We suggest conducting larger efficacy studies that also explore the functional effects of DBS in AN.

The neurocognitive basis of insight into illness in anorexia nervosa: a pilot metacognitive study

The primary goal of the present study was to explore the neuropsychological basis of insight into illness in anorexia nervosa by evaluating its differential and joint links with cognitive vs. metacognitive performance. Participants in the study were 25 women with anorexia nervosa (AN) and 25 healthy comparisons (HC). All participants completed a computerized version of the Wisconsin Card Sorting Task (WCST) and the Computerized Body-Size Discrimination task (CBSD). In addition to the standard administration of the tasks, subjects were also asked to rate their level of confidence in the correctness of each sort and to choose whether they wanted each sort to be "counted" toward their overall performance score on the test. Insight into illness in the AN group was assessed with the Scale of Unawareness of Mental Disorder (SUMD). Prediction of poor insight was significantly improved when adding the new, free-choice metacognitive measures to the conventional measures in both tasks, but not the other way around. These preliminary results suggest that metacognition might be an important mediator between basic cognitive deficits and poor insight and that it might be even more relevant to poor insight than cognitive deficits per se.

Altered insula response to sweet taste processing after recovery from anorexia and bulimia nervosa

OBJECTIVE

Recent studies suggest that altered function of higher-order appetitive neural circuitry may contribute to restricted eating in anorexia nervosa and overeating in bulimia nervosa. This study used sweet tastes to interrogate gustatory neurocircuitry involving the anterior insula and related regions that modulate sensory-interoceptive-reward signals in response to palatable foods.

METHOD

Participants who had recovered from anorexia nervosa and bulimia nervosa were studied to avoid confounding effects of altered nutritional state. Functional MRI measured brain response to repeated tastes of sucrose and sucralose to disentangle neural processing of caloric and noncaloric sweet tastes. Whole-brain functional analysis was constrained to anatomical regions of interest.

RESULTS

Relative to matched comparison women (N=14), women recovered from anorexia nervosa (N=14) had significantly diminished and women recovered from bulimia nervosa (N=14) had significantly elevated hemodynamic response to tastes of sucrose in the right anterior insula. Anterior insula response to sucrose compared with sucralose was exaggerated in the recovered group (lower in women recovered from anorexia nervosa and higher in women recovered from bulimia nervosa).

CONCLUSIONS

The anterior insula integrates sensory reward aspects of taste in the service of nutritional homeostasis. One possibility is that restricted eating and weight loss occur in anorexia nervosa because of a failure to accurately recognize hunger signals, whereas overeating in bulimia nervosa could represent an exaggerated perception of hunger signals. This response may reflect the altered calibration of signals related to sweet taste and the caloric content of food and may offer a pathway to novel and more effective treatments.

Altered brain reward circuits in eating disorders: chicken or egg?

The eating disorders anorexia nervosa (AN) and bulimia nervosa (BN) are severe psychiatric disorders with high mortality. Our knowledge about the neurobiology of eating disorders is very limited, and the question remains whether alterations in brain structure or function in eating disorders are state related, remnants of the illness or premorbid traits. The brain reward system is a relatively well-characterized brain circuitry that plays a central role in the drive to eat and individuals with current or past eating disorders showed alterations in those pathways compared to controls. Here we propose that structural and functional alterations in the insula and frontal cortex, including orbitofrontal and cingulate regions, areas that contribute to reward and anxiety processing, could predispose to developing an eating disorder and that adaptive changes in those circuits in response to malnutrition or repeated binge eating and purging could further promote illness behavior, hinder recovery and contribute to relapse.

Localized brain volume and white matter integrity alterations in adolescent anorexia nervosa

OBJECTIVE

The neurobiological underpinnings of anorexia nervosa (AN) are poorly understood. In this study, we tested whether brain gray matter (GM) and white matter (WM) in adolescents with AN would show alterations comparable to those in adults.

METHOD

We used magnetic resonance imaging to study GM and WM volume, and diffusion tensor imaging to assess fractional anisotropy for WM integrity in 19 adolescents with AN and 22 controls.

RESULTS

Individuals with AN showed greater left orbitofrontal, right insular, and bilateral temporal cortex GM, as well as temporal lobe WM volumes compared to controls. WM integrity in adolescents with AN was lower (lower fractional anisotropy) in fornix, posterior frontal, and parietal areas, but higher in anterior frontal, orbitofrontal, and temporal lobes. In individuals with AN, orbitofrontal GM volume correlated negatively with sweet taste pleasantness. An additional comparison of this study cohort with adult individuals with AN and healthy controls supported greater orbitofrontal cortex and insula volumes in AN across age groups.

CONCLUSIONS

This study indicates larger orbitofrontal and insular GM volumes, as well as lower fornix WM integrity in adolescents with AN, similar to adults. The pattern of larger anteroventral GM and WM volume as well as WM integrity, but lower WM integrity in posterior frontal and parietal regions may indicate that developmental factors such as GM pruning and WM growth could contribute to brain alterations in AN. The negative correlation between taste pleasantness and orbitofrontal cortex volume in individuals with AN could contribute to food avoidance in this disorder.

Alterations in brain structures related to taste reward circuitry in ill and recovered anorexia nervosa and in bulimia nervosa

OBJECTIVE

The pathophysiology of anorexia nervosa remains obscure, but structural brain alterations could be functionally important biomarkers. The authors assessed taste pleasantness and reward sensitivity in relation to brain structure, which may be related to food avoidance commonly seen in eating disorders.

METHOD

The authors used structural MR imaging to study gray and white matter volumes in women with current restricting-type anorexia nervosa (N=19), women recovered from restricting-type anorexia nervosa (N=24), women with bulimia nervosa (N=19), and healthy comparison women (N=24).

RESULTS

All eating disorder groups exhibited increased gray matter volume of the medial orbitofrontal cortex (gyrus rectus). Manual tracing confirmed larger gyrus rectus volume, and volume predicted taste pleasantness ratings across all groups. Analyses also indicated other morphological differences between diagnostic categories. Antero-ventral insula gray matter volumes were increased on the right side in the anorexia nervosa and recovered anorexia nervosa groups and on the left side in the bulimia nervosa group relative to the healthy comparison group. Dorsal striatum volumes were reduced in the recovered anorexia nervosa and bulimia nervosa groups and predicted sensitivity to reward in all three eating disorder groups. The eating disorder groups also showed reduced white matter in right temporal and parietal areas relative to the healthy comparison group. The results held when a range of covariates, such as age, depression, anxiety, and medications, were controlled for.

CONCLUSION

Brain structure in the medial orbitofrontal cortex, insula, and striatum is altered in eating disorders and suggests altered brain circuitry that has been associated with taste pleasantness and reward value.

A systematic review of the effects of neuromodulation on eating and body weight: evidence from human and animal studies

BACKGROUND

Eating disorders (ED) are chronic and sometimes deadly illnesses. Existing treatments have limited proven efficacy, especially in the case of adults with anorexia nervosa (AN). Emerging neural models of ED provide a rationale for more targeted, brain-directed interventions.

AIMS

This systematic review has examined the effects of neuromodulation techniques on eating behaviours and body weight and assessed their potential for therapeutic use in ED.

METHOD

All articles in PubMed, PsychInfo and Web of Knowledge were considered and screened against a priori inclusion/exclusion criteria. The effects of repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation, vagus nerve stimulation (VNS) and deep brain stimulation (DBS) were examined across studies in ED samples, other psychiatric and neurological disorders, and animal models.

RESULTS

Sixty studies were identified. There is evidence for ED symptom reduction following rTMS and DBS in both AN and bulimia nervosa. Findings from studies of other psychiatric and neurological disorders and from animal studies demonstrate that increases in food intake and body weight can be achieved following DBS and that VNS has potential value as a means of controlling eating and inducing weight loss.

CONCLUSIONS

Neuromodulation tools have potential for reducing ED symptomatology and related behaviours, and for altering food intake and body weight. In response to such findings, and emerging neural models of ED, treatment approaches are highly unlikely to remain 'brainless'. More research is required to evaluate the potential of neuromodulation procedures for improving long-term outcomes in ED.

The relationship between decision-making and perfectionism in obsessive-compulsive disorder and eating disorders

BACKGROUND AND OBJECTIVES

Obsessive-compulsive disorder (OCD) and eating disorders (EDs) show phenotypic similarities and have been independently associated with deficits in decision-making and maladaptive perfectionism. However, research directly comparing the two disorders is sparse and the significance of observed similarities remains in question. Therefore, the present study compared decision-making in OCD and EDs in relationship to perfectionistic personality traits.

METHODS

Sixty-one women were enrolled in the study comprising 3 mutually exclusive groups: 19 with OCD, 17 with EDs, and 21 healthy controls. Decision-making performance on the Iowa Gambling Task under two conditions, ambiguity and risk, was examined in relationship to perfectionistic traits.

RESULTS

Behavioral results indicated that EDs participants, relative to both OCD and control participants, were impaired in decision-making under conditions of risk. Heightened perfectionism was associated with less risky decision-making in OCD, but more risky decision-making in EDs.

LIMITATIONS

Sample size was small and all participants were women, which may limit generalizability.

CONCLUSION

Results support decision-making deficits in EDs, which may be related to a dysfunctional determination of risk versus reward. This study is the first to suggest that the relationship between perfectionism and risk taking may manifest differently in these phenotypically similar disorders.

Rumination and modes of processing around meal times in women with anorexia nervosa: qualitative and quantitative results from a pilot study

OBJECTIVE

The primary aim of this exploratory study was to examine qualitatively and quantitatively the effects of rumination, mindful breathing, and distraction on processing styles and the meal time experience in women with a history of anorexia nervosa (AN).

METHOD

A quasi-experimental within-participant design was employed. Thirty-seven women with history of AN and all experiencing current eating disorder psychopathology listened to a single rumination, mindful breathing and distraction exercise before a meal time. Qualitative and quantitative analyses were employed.

RESULTS

Specific themes were extracted for each exercise including avoidance, being in the moment and rumination. The rumination exercise led to significantly greater analytical self-focus. Mindful breathing led to significantly greater experiential self-focus compared with distraction in partially weight-restored AN participants.

CONCLUSIONS

In AN, self-material is processed in a ruminative way and avoidance is valued. It is difficult to shift individuals with AN out of a rumination around meal times using brief mindful breathing. Future research should investigate at what stage of AN illness mindful-based and acceptance-based strategies are useful and how these strategies could be incorporated in treatment.

Catechol-O-methyltransferase genotype modifies executive functioning and prefrontal functional connectivity in women with anorexia nervosa

BACKGROUND

Anorexia nervosa is characterized by high levels of perseveration and inflexibility, which interfere with successful treatments. Dopamine (DA) signalling seems to play a key role in modulating the prefrontal cortex, since both DA deficiency and excess nega tively influence the efficiency of cognitive functions. The present study explores the effect of a functional polymorphism (Val158Met) in the catechol-O-methyltransferase (COMT) gene on the set-shifting abilities and prefrontal functional connectivity of patients with anorexia nervosa.

METHODS

All participants performed the Wisconsin Card Sorting Task, and a subsample underwent resting-state functional magnetic resonance imaging.

RESULTS

We included 166 patients with DSM-IV lifetime anorexia nervosa and 140 healthy women in our study. Both underweight and weight-recovered patients with anorexia nervosa showed high levels of perseveration, but only in the underweight group did the Val158Met polymorphism affect cognitive performance, showing the U-shaped curve characteristic of increased DA signalling in the prefrontal cortex. Underweight patients with anorexia nervosa who are Met homozygotes had significantly higher levels of perseveration and increased prefrontal functional connectivity than underweight patients in the other genotype groups, indicating abnormal regional cortical processing.

LIMITATIONS

Although our data show that grey matter reduction in starving patients with anorexia nervosa did not explain our findings, the cross-sectional design of the present study did not allow us to distinguish between the effects of starvation and those of low estrogen levels.

CONCLUSION

Starvation affects DA release in the prefrontal cortex of patients with anorexia nervosa with different effects on executive functioning and prefrontal functional connectivity according to the COMT genotype. This observation has several therapeutic implications that need to be addressed by future studies.

Neurocircuit function in eating disorders

OBJECTIVE

Eating disorders are serious psychosomatic disorders with high morbidity and lifetime mortality. Inadequate response to current therapeutic interventions constitutes a challenging clinical problem. A better understanding of the underlying neurobiological mechanisms could improve psychotherapeutic and drug treatment strategies.

METHOD

A review highlighting the current state of brain imaging in eating disorders related to the anxiety and pathological fear learning model of anorexia nervosa (AN) and the impulsivity model of binge eating in bulimia nervosa (BN).

RESULTS

Available neuroimaging studies in patients with acute AN primarily suggest a hyper-responsive emotional and fear network to food, but not necessarily to eating disorder-unrelated, salient stimuli. Furthermore, patients with AN show decreased activation in the ventral fronto-striatal circuits during the performance of a cognitive flexibility task. Results in patients with BN primarily suggest a hypo-responsive reward system to food stimuli, especially to taste reward. Additionally, patients with BN exhibit impaired brain activation in the inhibitory control network during the performance of general response-inhibition tasks.

DISCUSSION

Anxiety and pathological fear learning may lead to conditioned neural stimulus-response patterns to food stimuli and increased cognitive rigidity, which could account for the phobic avoidance of food intake in patients with acute AN. However, further neurobiological studies are required to investigate pathological fear learning in patients with AN. Patients with BN may binge eat to compensate for a hypo-responsive reward system. The impaired brain activation in the inhibitory control network may facilitate the loss of control over food intake in patients with BN.

Impaired inhibitory control in anorexia nervosa elicited by physical activity stimuli

Besides food restriction, hyperactivity is considered a key behavioral trait of anorexia nervosa (AN), playing a major role in the pathogenesis and progression of the disorder. However, the underlying neurophysiology remains poorly understood. We used functional magnetic resonance imaging during two affective go/no-go tasks to probe inhibitory control in response to stimuli depicting physical activity vs inactivity and food vs non-food in AN patients compared with 26 healthy athlete and non-athlete controls. We hypothesized that neural correlates of behavioral inhibition are biased by the emotional information of the stimuli in AN patients, leading to a differential neural inhibitory pattern during the two tasks. Indeed, we found reduced response inhibition for food and non-food images in the putamen, while stimuli depicting physical activity resulted in an exaggerated response of the prefrontal cortex (PFC) and cerebellum in AN patients. However, both AN patients and athletes revealed an increased response in the somatosensory cortex to physical activity stimuli. These results suggest that physical activity stimuli might place an increased demand on the inhibitory control system in AN patients. The resulting hyperactivity of the PFC and cerebellum may lead to altered executive function and motor control, sustaining increased physical activity in AN patients.

A rat in the labyrinth of anorexia nervosa: contributions of the activity-based anorexia rodent model to the understanding of anorexia nervosa

Activity-based anorexia (ABA) is an analogous animal model of anorexia nervosa where food-restricted rats develop excessive running activity when given free access to a running wheel; their body weight sharply decreases, and finally self-starvation and death ensue unless animals are removed from the experimental conditions. The parallel of this animal model with major signs in the human disorder has been the focus of much attention from researchers and clinicians as a platform for translational research. The paper reviews the historical antecedents of ABA, research characterizing its occurrence, and its main limitations and strengths as a model of AN. As a symptomatic model of AN, the ABA model can provide clinicians with innovative and alternative routes for improving the treatment of AN.

The enigmatic persistence of anorexia nervosa

OBJECTIVE

In this review, based on recent advances in cognitive neuroscience, the author presents a formulation in which the marked persistence of anorexia nervosa can be usefully understood as a well-ingrained maladaptive habit.

METHOD

The author reviewed the relevant literature on the development and course of anorexia nervosa and interpreted critical features in light of developments in cognitive neuroscience.

RESULTS

Anorexia nervosa is a well characterized disorder with remarkable persistence both across history and among affected individuals. Food restriction, the salient behavioral feature of the disorder, often begins innocently but gradually takes on a life of its own. Over time, it becomes highly entrenched and resistant to change through either psychological or pharmacological treatment. Cognitive neuroscience has described two related but distinct processes that underlie the acquisition of new patterns of behavior, namely, action-outcome and stimulus-response learning. It is likely that both processes are engaged in the development of anorexia nervosa and that stimulus-response learning (that is, habit formation) is critical to the persistence of the dieting behavior.

CONCLUSIONS

The formulation of the dieting behavior characteristic of anorexia nervosa as a well-entrenched habit provides a basis for understanding the striking persistence of this disorder. This model helps explain the resistance of anorexia nervosa to interventions that have established efficacy in related disorders and implies that addressing the dieting behavior is critical, especially early in the course of the illness, before it has become ingrained.

Caloric restriction enhances fear extinction learning in mice

Fear extinction learning, the ability to reassess a learned cue of danger as safe when it no longer predicts aversive events, is often dysregulated in anxiety disorders. Selective serotonin reuptake inhibitors (SSRI's) enhance neural plasticity and their ability to enhance fear extinction learning may explain their anxiolytic properties. Caloric restriction (CR) has SSRI-like effects on neural plasticity and anxiety-related behavior. We implemented CR in mice to determine its effects on conditioned-fear responses. Wild type and serotonin transporter (SERT) knockout mice underwent CR for 7 days leading to significant weight loss. Mice were then tested for cued fear learning and anxiety-related behavior. CR markedly enhanced fear extinction learning and its retention in adolescent female mice, and adults of both sexes. These effects of CR were absent in SERT knockout mice. Moreover, CR phenocopied behavioral and molecular effects of chronic fluoxetine, but there was no additive effect of CR in fluoxetine-treated mice. These results demonstrate that CR enhances fear extinction learning through a SERT-dependent mechanism. These results may have implications for eating disorders such as anorexia nervosa (AN), in which there is a high prevalence of anxiety before the onset of dietary restriction and support proposals that in AN, CR is a motivated effort to control dysregulated fear responses and elevated anxiety.

Does a shared neurobiology for foods and drugs of abuse contribute to extremes of food ingestion in anorexia and bulimia nervosa?

Is starvation in anorexia nervosa (AN) or overeating in bulimia nervosa (BN) a form of addiction? Alternatively, why are individuals with BN more vulnerable and individuals with AN protected from substance abuse? Such questions have been generated by recent studies suggesting that there are overlapping neural circuits for foods and drugs of abuse. To determine whether a shared neurobiology contributes to eating disorders and substance abuse, this review focused on imaging studies that investigated response to tastes of food and tasks designed to characterize reward and behavioral inhibition in AN and BN. BN and those with substance abuse disorders may share dopamine D2 receptor-related vulnerabilities, and opposite findings may contribute to "protection" from substance abuse in AN. Moreover, imaging studies provide insights into executive corticostriatal processes related to extraordinary inhibition and self-control in AN and diminished inhibitory self-control in BN that may influence the rewarding aspect of palatable foods and likely other consummatory behaviors. AN and BN tend to have premorbid traits, such as perfectionism and anxiety that make them vulnerable to using extremes of food ingestion, which serve to reduce negative mood states. Dysregulation within and/or between limbic and executive corticostriatal circuits contributes to such symptoms. Limited data support the hypothesis that reward and inhibitory processes may contribute to symptoms in eating disorders and addictive disorders, but little is known about the molecular biology of such mechanisms in terms of shared or independent processes.

Increased prefrontal and parahippocampal activation with reduced dorsolateral prefrontal and insular cortex activation to food images in obesity: a meta-analysis of fMRI studies

Background and Objectives

Obesity is emerging as the most significant health concern of the twenty-first century. A wealth of neuroimaging data suggest that weight gain might be related to aberrant brain function, particularly in prefrontal cortical regions modulating mesolimbic addictive responses to food. Nevertheless, food addiction is currently a model hotly debated. Here, we conduct a meta-analysis of neuroimaging data, examining the most common functional differences between normal-weight and obese participants in response to food stimuli.

Data Source

We conducted a search using several journal databases and adhered to the ‘Preferred Reporting Items for Systematic Reviews and Meta-analyses’ (PRISMA) method. To this aim, 10 studies were found with a total of 126 obese participants, 129 healthy controls, equaling 184 foci (146 increased, 38 decreased activation) using the Activation Likelihood Estimation (ALE) technique. Out of the 10 studies, 7 investigated neural responses to food versus non-food images.

Results

In response to food images, obese in comparison to healthy weight subjects had increased activation in the left dorsomedial prefrontal cortex, right parahippocampal gyrus, right precentral gyrus and right anterior cingulate cortex, and reduced activation in the left dorsolateral prefrontal cortex and left insular cortex.

Conclusions

Prefrontal cortex areas linked to cognitive evaluation processes, such as evaluation of rewarding stimuli, as well as explicit memory regions, appear most consistently activated in response to images of food in those who are obese. Conversely, a reduced activation in brain regions associated with cognitive control and interoceptive awareness of sensations in the body might indicate a weakened control system, combined with hypo-sensitivity to satiety and discomfort signals after eating in those who are prone to overeat.

Anorexia nervosa during adolescence and young adulthood: towards a developmental and integrative approach sensitive to time course

Anorexia nervosa is situated at the junction between two time scales, the time scale of adolescence, in which intense physiological and psychological upheavals are occurring over a relatively short period of time, and the time scale of the potentially chronic evolution of the disease over the course of the patient's lifespan. This second time scale links the critical period of adolescence with the pre-morbid period, during which a complex state of vulnerability, often unseen and unheard, combines with different risk factors, which may be isolated, associated, dissociated or concomitant, to produce the emergence of anorexia; it ushers also adolescence into the period of adulthood, flagged with the reorganization that occurs in the course of the healing process (in case of recovery), or pervaded by somatic and mental distress (in cases where the condition becomes chronic). Given the lifespan nature of the disease, it is difficult to differentiate premorbid pathogenic factors from changes resulting from the acute or chronic phases of the illness. It is also difficult to establish straightforward correlations between physiological disturbances and their clinical consequences, or conversely to assume that the restoration of physiological parameters means the disappearance of the underlying mental disorder. Taken together, these observations support an approach to anorexia nervosa that is both developmental and integrative, taking into account both the complexity of the pathways involved and the developmental timescales of these pathways. This type of approach can help to adjust therapeutic strategies and thus enhance prognosis, in particular by integrating the temporal parameter into the dynamics of care plans.

Adolescent female C57BL/6 mice with vulnerability to activity-based anorexia exhibit weak inhibitory input onto hippocampal CA1 pyramidal cells

Anorexia nervosa (AN) is an eating disorder characterized by self-imposed severe starvation and often linked with excessive exercise. Activity-based anorexia (ABA) is an animal model that reproduces some of the behavioral phenotypes of AN, including the paradoxical increase in voluntary exercise following food restriction (FR). Although certain rodents have been used successfully in this animal model, C57BL/6 mice are reported to be less susceptible to ABA. We re-examined the possibility that female C57BL/6 mice might exhibit ABA vulnerability during adolescence, the developmental stage/sex among the human population with particularly high AN vulnerability. After introducing the running wheel to the cage for 3 days, ABA was induced by restricting food access to 1h per day (ABA1, N=13) or 2 h per day (ABA2, N=10). All 23 exhibited increased voluntary wheel running (p<0.005) and perturbed circadian rhythm within 2 days. Only one out of five survived ABA1 for 3 days, while 10 out of 10 survived ABA2 for 3 days and could subsequently restore their body weight and circadian rhythm. Exposure of recovered animals to a second ABA2 induction revealed a large range of vulnerability, even within littermates. To look for the cellular substrate of differences in vulnerability, we began by examining synaptic patterns in the hippocampus, a brain region that regulates anxiety as well as plasticity throughout life. Quantitative EM analysis revealed that CA1 pyramidal cells of animals vulnerable to the second ABA2 exhibit less GABAergic innervation on cell bodies and dendrites, relative to the animals resilient to the second ABA (p<0.001) or controls (p<0.05). These findings reveal that C57BL/6J adolescent females can be used to capture brain changes underlying ABA vulnerability, and that GABAergic innervation of hippocampal pyramidal neurons is one important cellular substrate to consider for understanding the progression of and resilience to AN.

Liking compared with wanting for high- and low-calorie foods in anorexia nervosa: aberrant food reward even after weight restoration

BACKGROUND

Recent frameworks for understanding food rewards recognize the role of separable affective and motivational processes (liking and wanting) in driving human eating behavior. Separate assessments of liking and wanting may aid in understanding the complex eating-related behaviors seen in anorexia nervosa (AN).

OBJECTIVE

The aim of this study was to examine separately liking and wanting for foods of different energy densities in women at different stages of AN and in healthy volunteers at both an implicit and an explicit level.

DESIGN

Explicit liking and wanting responses to high- and low-calorie foods were derived from analog ratings, whereas an implicit "wanting" measure was identified by using reaction time in a forced-choice procedure. Explicit and implicit processes were compared across 3 groups of AN participants (current AN, weight-restored AN, and recovered AN) and healthy volunteers.

RESULTS

Currently underweight AN participants explicitly wanted high-calorie foods less than did the other groups. Both current and weight-restored AN groups demonstrated significantly less implicit "wanting" for high-calorie foods and more implicit "wanting" for low-calorie foods-an inverted pattern to never-ill participants.

CONCLUSIONS

The aberrant responses to food that characterize AN may be driven more by altered motivational salience ("wanting") than by explicit liking responses. This pattern of aberrant food reward appears to be independent of weight status. Examining the processes that motivate approach or avoidance of low- and high-calorie foods in AN may aid the development of targeted strategies to augment existing interventions.

Dysfunctions of leptin, ghrelin, BDNF and endocannabinoids in eating disorders: beyond the homeostatic control of food intake

A large body of literature documents the occurrence of alterations in the physiology of both central and peripheral modulators of appetite in acute patients with anorexia nervosa (AN) and bulimia nervosa (BN). Until more recently the role of most of the appetite modulators in the control of eating behavior was conceptualized solely in terms of their influence on homeostatic control of energy balance. However, it is becoming more and more evident that appetite modulators also affect the non-homeostatic cognitive, emotional and rewarding component of food intake as well as non food-related reward, and, recently, AN and BN have been pathophysiologically linked to dysfunctions of reward mechanisms. Therefore, the possibility exists that observed changes in appetite modulators in acute AN and BN may represent not only homeostatic adaptations to malnutrition, but also contribute to the development and/or the maintenance of aberrant non-homeostatic behaviors, such as self-starvation and binge eating. In the present review, the evidences supporting a role of leptin, ghrelin, brain-derived neurotrophic factor and endocannabinoids in the homeostatic and non-homeostatic dysregulations of patients with AN and BN will be presented. The reviewed literature is highly suggestive that changes in the physiology of these modulators may play a pivotal role in the pathophysiology of eating disorders by providing a possible link between motivated behaviors, reward processes, cognitive functions and energy balance.

The role of psychosocial factors and psychiatric disorders in functional dyspepsia

In this Review, after a brief historical introduction, we first provide an overview of epidemiological studies that demonstrate an association between functional dyspepsia and psychological traits, states or psychiatric disorders. These studies suggest an important intrinsic role for psychosocial factors and psychiatric disorders, especially anxiety and depression, in the aetiopathogenesis of functional dyspepsia, in addition to their putative influence on health-care-seeking behaviour. Second, we describe pathophysiological evidence on how psychosocial factors and psychiatric disorders might exert their role in functional dyspepsia. Novel insights from functional brain imaging studies regarding the integration of gut-brain signals, processed in homeostatic-interoceptive brain regions, with input from the exteroceptive system, the reward system and affective and cognitive circuits, help to clarify the important role of psychological processes and psychiatric morbidity. We therefore propose an integrated model of functional dyspepsia as a disorder of gut-brain signalling, supporting a biopsychosocial approach to the diagnosis and management of this disorder.

Nothing tastes as good as skinny feels: the neurobiology of anorexia nervosa

Individuals with anorexia nervosa (AN) engage in relentless restrictive eating and often become severely emaciated. Because there are no proven treatments, AN has high rates of relapse, chronicity, and death. Those with AN tend to have childhood temperament and personality traits, such as anxiety, obsessions, and perfectionism, which may reflect neurobiological risk factors for developing AN. Restricted eating may be a means of reducing negative mood caused by skewed interactions between serotonin aversive or inhibitory and dopamine reward systems. Brain imaging studies suggest that altered eating is a consequence of dysregulated reward and/or awareness of homeostatic needs, perhaps related to enhanced executive ability to inhibit incentive motivational drives. An understanding of the neurobiology of this disorder is likely to be important for developing more effective treatments.