What can food-image tasks teach us about anorexia nervosa? A systematic review

Exploring the neurofunctional impairments and cognitive biases concerning food and body related stimuli in anorexia nervosa: An integrated EEG and eye-tracking study protocol

BACKGROUND

Patients with Anorexia Nervosa (AN) exhibit significant cognitive and neural disturbances compared to healthy individuals when processing food and body-related stimuli. These disturbances not only contribute to the manifestation and chronification of their pathological eating behaviour but also underscore the complex interplay of cognitive, emotional, and neurobiological factors in AN. However, the precise underlying cognitive and neural mechanisms of these disturbances remain a compelling area of investigation.

METHODS

This study presents a protocol developed for conducting a cross-sectional quasi-experimental study using a mixed model ANOVA approach with a crossover design. Our participants will consist of 20 patients with an active diagnosis of AN, 20 Overweight/obese individuals, and 20 Healthy Controls (HCs) with a normal BMI. An integrated eye-tracking and EEG methodology will be used in conjunction, with the primary aim of assessing participants' cognitive and neural processing towards high and low-calorie food stimuli. On an exploratory level, by utilizing the same methods, the present study will also investigate AN patients' responses towards high weight, normal weight, low weight, and self-body pictures, as well as towards images from the International Affective Picture System (IAPS) characterized by elevated valence and arousal levels. Additionally, behavioural methods such as yes or no questions, and self-reported questionnaires will be administered. The EEG and eye-tracking data will be analysed at early (50-300 ms) and late (350-500 ms) time intervals.

DISCUSSION

The investigation of the underlying cognitive and neural processes employed by patients with AN during the processing of food and body-related stimuli can help us develop a better understanding of the cognitive and neural mechanisms that contribute to the manifestation and maintenance of the disorder and assist in the development of more effective screening methods.

ETHICAL APPROVAL AND CONSENT TO PARTICIPATE

Ethical approval for the study has been obtained by the Cyprus National Bioethics Committee on 27.04.2023 (ΕΕΒΚ/ΕΠ/2023/19), and by the University of Cyprus (20.02.2023). Written informed consent will be obtained from all participants.

Measuring implicit associations between food and body stimuli in anorexia nervosa: a Go/No-Go Association Task

PURPOSE

The present study aimed to explore the implicit associations between food and bodily stimuli in patients with anorexia nervosa (AN) and control subjects (HC).

METHODS

A Go/No-Go Association Task was administrated to 55 participants (28 AN and 27 HC), using food stimuli (low-calorie food vs. high-calorie food) and body stimuli (underweight vs. overweight bodies).

RESULTS

We evidenced an implicit association between food and body stimuli in the AN group, whereas the HC group only showed a tendency. AN and HC groups also exhibited different categorization strategies: the AN group tended to categorize stimuli as low-calorie foods and underweight bodies less than the HC group, and they tended to categorize stimuli as high-calorie foods and overweight bodies more than the HC group.

CONCLUSION

The present study revealed for the first time specificities of the AN population's implicit association between food and body stimuli in terms of association strength and categorization strategy. Furthermore, the results suggest that combining implicit methodologies with other methods could contribute to a better characterization of the physiopathology of AN.

LEVEL OF EVIDENCE

Level I, experimental study.

Emotional food-cue-reactivity in anorexia nervosa and bulimia nervosa: An electroencephalography study

OBJECTIVE

Food-cue-reactivity entails neural and experiential responses to the sight and smell of attractive foods. Negative emotions can modulate such cue-reactivity and this might be central to the balance between restrictive versus bulimic symptomatology in Anorexia Nervosa (AN) and Bulimia Nervosa (BN).

METHOD

Pleasantness ratings and electrocortical responses to food images were measured in patients with AN (n = 35), BN (n = 32) and matched healthy controls (HC, n = 35) in a neutral state and after idiosyncratic negative emotion induction while electroencephalography (EEG) was recorded. The EEG data were analyzed using a mass testing approach.

RESULTS

Individuals with AN showed reduced pleasantness for foods compared to objects alongside elevated widespread occipito-central food-object discrimination between 170 and 535 ms, indicative of strong neural cue-reactivity. Food-object discrimination was further increased in the negative emotional condition between 690 and 1200 ms over centroparietal regions. Neither of these effects was seen in individuals with BN.

DISCUSSION

Emotion modulated food-cue-reactivity in AN might reflect a decreased appetitive response in negative mood. Such specific (emotion-)regulatory strategies require more theoretical work and clinical attention. The absence of any marked effects in BN suggests that emotional cue-reactivity might be less prominent in this group or quite specific to certain emotional contexts or food types.

PUBLIC SIGNIFICANCE

Negative affectivity is a risk factor for the development of eating disorders and individuals with eating disorders experience problems with emotion regulation. To better understand the effects of negative emotions, the present study investigated how they affected neural correlates of food perception in anorexia nervosa and bulimia nervosa.

Attentional bias to food during free and instructed viewing in anorexia nervosa: An eye tracking study

Previous research has shown that patients with anorexia nervosa (AN) show an attentional bias to food. However, due to different conceptualizations of attentional bias and the use of various paradigms, results are inconclusive and more precise insights into the exact nature of this attentional bias are needed. Therefore, an eye-tracking paradigm with food (low and high caloric) and non-food (objects) pictures was used to investigate biases in AN patients (n = 25) compared to healthy controls (n = 22). Several indices of visual attention were examined, both during free (initial orientation, fixation frequency, fixation time) and explicitly instructed (engagement, disengagement) viewing. Our results during the free viewing phase indicated that AN patients (as compared to healthy matched controls) looked less frequently and spent less time fixating on food stimuli, compared to the comparison group. No differences between both groups (n = 47) in initial orientation could be observed. Interestingly, during the instructed viewing phase, no differences between the patient and the comparison group were observed in engagement or disengagement to food stimuli. These results suggest an (initial) attentional avoidance of food in AN patients when closely investigating spontaneous attentional processes, while this could not be observed during gaze behaviour when receiving clear instructions. Hence, future research should look into how attentional bias during spontaneous gaze patterns could serve as a potential marker of AN, and how targeting this bias could be applied in treatment interventions.

Food induced distractibility in restrictive anorexia nervosa: Different motor patterns for different foods as revealed by a mouse tracker evaluation

An altered automatic processing of food stimuli may contribute to the maintenance of calorie restriction in patients with restrictive Anorexia Nervosa (AN-R). The present study aimed to assess whether task-irrelevant food distractors elicited a different interference effect in the motor actions of patients with AN-R compared to healthy controls (HC). 40 patients with acute AN-R and 40 HC performed an irrelevant distractor task in which they were required to perform a reaching movement from a starting point to a green dot, while an irrelevant distractor (a high-calorie food, low-calorie food, or neutral object) was presented in the middle of the screen. Mouse trajectories and response times (RT) were recorded. The analyses conducted on the kinematic variables revealed that while the trajectories of HC veered similarly toward the three categories of stimuli, AN-R patients showed an increased deviation toward low-calorie foods and a reduced deviation toward high-calorie foods compared to neutral objects. No significant results emerged as regards RT. The pattern of responses observed in patients with AN-R (deviation increased toward low-calorie and reduced toward high-calorie) is consistent with their eating habits and may thus represent an implicit mechanism sustaining calorie restriction in patients with AN-R.

Neural activation of regions involved in food reward and cognitive control in young females with anorexia nervosa and atypical anorexia nervosa versus healthy controls

Anorexia nervosa (AN) and atypical AN (AtypAN) are complex neurobiological illnesses that typically onset in adolescence with an often treatment-refractory and chronic illness trajectory. Aberrant eating behaviors in this population have been linked to abnormalities in food reward and cognitive control, but prior studies have not examined respective contributions of clinical characteristics and metabolic state. Research is needed to identify specific disruptions and inform novel intervention targets to improve outcomes. Fifty-nine females with AN (n = 34) or AtypAN (n = 25), ages 10-22 years, all ≤90% expected body weight, and 34 age-matched healthy controls (HC) completed a well-established neuroimaging food cue paradigm fasting and after a standardized meal, and we used ANCOVA models to investigate main and interaction effects of Group and Appetitive State on blood oxygenation level-dependent (BOLD) activation for the contrast of exposure to high-calorie food images minus objects. We found main effects of Group with greater BOLD activation in the dorsal anterior cingulate cortex (dACC), dorsolateral prefrontal cortex (DLPFC), hippocampus, caudate, and putamen for AN/AtypAN versus HC groups, and in the three-group model including AN, AtypAN, and HC (sub-)groups, where differences were primarily driven by greater activation in the AtypAN subgroup versus HC group. We found a main effect of Appetitive State with increased premeal BOLD activation in the hypothalamus, amygdala, nucleus accumbens, and caudate for models that included AN/AtypAN and HC groups, and in BOLD activation in the nucleus accumbens for the model that included AN, AtypAN, and HC (sub-)groups. There were no interaction effects of Group with Appetitive State for any of the models. Our findings demonstrate robust feeding-state independent group effects reflecting greater neural activation of specific regions typically associated with reward and cognitive control processing across AN and AtypAN relative to healthy individuals in this food cue paradigm. Differential activation of specific brain regions in response to the passive viewing of high-calorie food images may underlie restrictive eating behavior in this clinical population.

Trait anxiety is associated with amygdala expectation and caloric taste receipt response across eating disorders

Anxious traits are elevated in eating disorders (EDs), are considered risk factors for ED development, and trait anxiety has been linked to ED psychopathology. How trait anxiety relates to ED neurobiology is not well understood. In this study 197 individuals across the ED spectrum (anorexia nervosa n = 91; other specified EDs n = 34; bulimia nervosa n = 56; binge ED n = 16), and 120 healthy controls were assessed for anxious traits and learned to expect and receive caloric or neutral taste stimuli during brain imaging. Amygdala sucrose expectation response differed across groups (Wilk's lambda = 0.945, p = 0.023), and was higher on the left in anorexia nervosa compared to healthy controls (p = 0.002). Expected sucrose receipt response across taste reward regions was not different between groups. In the ED sample, trait anxiety negatively moderated the relationship between amygdala expectation and right dorsal (p = 0.0062) and ventral (p = 0.0046) anterior insula receipt response. A subgroup analysis showed similar results for anorexia nervosa, and partially in bulimia nervosa. Across EDs, appetitive motivation correlated positively with bilateral orbitofrontal cortex, caudate head, and ventral striatal sucrose receipt response (r = 0.215 to 0.179, p = 0.002 to 0.012). Across the study sample, trait anxiety showed an inverted-U-shaped relationship with right (r = 0.147, p = 0.034) and left (r = 0.162, p = 0.016) amygdala expectation response. Amygdala sucrose expectation response is elevated in anorexia nervosa, correlates with sucrose receipt response, and this relationship is negatively moderated by trait anxiety across EDs. Trait anxiety may have an important role in how expectation drives taste stimulus receipt brain response and perhaps food approach in individuals with EDs.

Neural correlates associated with processing food stimuli in anorexia nervosa and bulimia nervosa: an activation likelihood estimation meta-analysis of fMRI studies

PURPOSE

Various neurobiological models have utilised symptom categories to explore the underlying neural correlates in both anorexia nervosa (AN) and bulimia nervosa (BN). The aim of this research was to investigate the brain activity patterns associated with viewing food stimuli in anorexia nervosa and bulimia nervosa.

METHODS

Electronic databases including PsycInfo and PubMed were systematically searched from data base inception until 1st of December 2020, identifying 14 suitable functional magnetic resonance imaging studies (fMRI), involving 470 participants. ALE meta-analysis was used to statistically analyse the overlap of activation foci from different fMRI studies in response to visual food stimuli.

RESULTS

Comparing patients with AN with healthy control (HC), we detected hypoactivation in brain areas related to reward processing (i.e., amygdala and lentiform nucleus), and interoceptive processing (i.e., insula). In addition, patients with AN showed hyperactivations in cognitive control areas (i.e., prefrontal and anterior cingulate cortex). In contrast, patients with BN exhibited hyperactivations in brain areas related to reward processing (i.e., lentiform nucleus), and interoceptive processing (i.e., insula). Furthermore, patients with BN showed hypoactivations in brain regions associated with cognitive control (i.e., prefrontal and anterior cingulate cortex).

CONCLUSIONS

Our study shows differing neural endotypes of the two types of eating disorders, that underpin their behavioural phenotypes. While exploratory in nature, these findings might be relevant for guiding new emerging therapies, including invasive and non-invasive neuromodulation techniques in treatment of eating disorders.

LEVEL OF EVIDENCE

Level I, meta-analysis.

Restrictive eating across a spectrum from healthy to unhealthy: behavioral and neural mechanisms

BACKGROUND

Restriction of food intake is a central feature of anorexia nervosa (AN) and other eating disorders, yet also occurs in the absence of psychopathology. The neural mechanisms of restrictive eating in health and disease are unclear.

METHODS

This study examined behavioral and neural mechanisms associated with restrictive eating among individuals with and without eating disorders. Dietary restriction was examined in four groups of women (n = 110): healthy controls, dieting healthy controls, patients with subthreshold (non-low weight) AN, and patients with AN. A Food Choice Task was administered during fMRI scanning to examine neural activation associated with food choices, and a laboratory meal was conducted.

RESULTS

Behavioral findings distinguished between healthy and ill participants. Healthy individuals, both dieting and non-dieting, chose significantly more high-fat foods than patients with AN or subthreshold AN. Among healthy individuals, choice was primarily influenced by tastiness, whereas, among both patient groups, healthiness played a larger role. Dorsal striatal activation associated with choice was most pronounced among individuals with AN and was significantly associated with selecting fewer high-fat choices in the task and lower caloric intake in the meal the following day.

CONCLUSIONS

A continuous spectrum of behavior was suggested by the increasing amount of weight loss across groups. Yet, data from this Food Choice Task with fMRI suggest there is a behavioral distinction between illness and health, and that the neural mechanisms underlying food choice in AN are distinct. These behavioral and neural mechanisms of restrictive eating may be useful targets for treatment development.

Gastrointestinal Interoception in Eating Disorders: Charting a New Path

PURPOSE OF REVIEW

Abnormal interoception has been consistently observed across eating disorders despite limited inclusion in diagnostic conceptualization. Using the alimentary tract as well as recent developments in interoceptive neuroscience and predictive processing as a guide, the current review summarizes evidence of gastrointestinal interoceptive dysfunction in eating disorders.

RECENT FINDINGS

Eating is a complex process that begins well before and ends well after food consumption. Abnormal prediction and prediction-error signals may occur at any stage, resulting in aberrant gastrointestinal interoception and dysregulated gut sensations in eating disorders. Several interoceptive technologies have recently become available that can be paired with computational modeling and clinical interventions to yield new insights into eating disorder pathophysiology. Illuminating the neurobiology of gastrointestinal interoception in eating disorders requires a new generation of studies combining experimental probes of gut physiology with computational modeling. The application of such techniques within clinical trials frameworks may yield new tools and treatments with transdiagnostic relevance.

I change my mind to get better: Process tracing-based microanalysis of food choice processes reveals differences between anorexia nervosa and bulimia nervosa during inpatient treatment

Food choice and its underlying processes is understudied in bulimia nervosa (BN) and anorexia nervosa (AN). Thus, we examined cognitive processes during food choice through mouse tracing in AN (n = 36) and BN (n = 27) undergoing inpatient treatment. Both patient groups and matched healthy controls (HC, n = 59) made 153 binary food choices before rating all foods on their liking and calorie density. Choice outcomes and corresponding mouse movements were modelled as a function of inpatient treatment stage in our analyses. Compared to patients with BN and HC, those with AN showed a clear calorie avoidance on most trials. Yet, mouse paths in AN patients early in treatment, revealed a late direction reversal ('change of mind', CoM) on high-calorie choices. AN patients later in treatment, by contrast, showed fewer CoM alongside more choices for - and liking of - high-calorie foods. Patients with BN showed more CoM trials during low-calorie choices and low-calorie choices were more frequent in patients later in treatment. Thus, relative to patients early in treatment, patients who are later in treatment show less of the overall group pattern of consistently choosing low-calorie food (AN) or high-calorie food (BN). Less cognitive regulation (fewer CoM trials) went along with higher liking for high-calorie foods in AN. These cross-sectional differences between AN early and late in treatment might reflect the formation of healthier habits. In addition, clear patient group differences suggest more specific treatment strategies.

Aberrant neural representation of food stimuli in women with acute anorexia nervosa predicts treatment outcome and is improved in weight restored individuals

Anorexia nervosa (AN) has been associated with altered reward processing. We recently reported greater neural response in secondary visual areas when processing visual food stimuli in acutely underweight AN patients (acAN). In order to examine whether the observed alterations are indicative of acute undernutrition or a potential trait marker of AN, we set out to assess neural responses in acAN and in individuals weight-recovered from AN (recAN). FMRI data were collected from a total of 126 female volunteers, 35 acAN, 33 recAN, and 58 age-matched healthy controls (HC) while they viewed streams of food, social and neutral stimuli. A standard general linear model (GLM) was used to interrogate neural responses to the different stimuli in recAN vs. age-matched HC. Moreover, within-subject multivoxel pattern analyses (MVPA) in the two matched samples (acAN/HC and recAN/HC) were used to estimate neural representation of food vs. neutral, and social vs. neutral stimuli. A multiple regression analysis was conducted to test associations between the accuracy of the neural representation and treatment outcome. The GLM revealed no group differences between recAN and HC. The MVPAs showed greater classification accuracy of food stimuli in the posterior fusiform gyrus in acAN but not recAN. Classification accuracy was associated with better treatment outcome. Our findings suggest that the neural representation of food stimuli is altered in secondary visual areas in acAN and normalizes with weight recovery. Possibly this altered representation reflects attentional engagement motivating food intake, which may promote the recovery process.

Bad mood food? Increased versus decreased food cue reactivity in anorexia nervosa and bulimia nervosa during negative emotions

OBJECTIVE

Emotion regulation difficulties in anorexia nervosa (AN) and bulimia nervosa (BN) might underlie bingeing and purging in BN, extreme fasting in AN, or combinations of these symptoms in binge-purge type AN. In this study, we tested for decreased food cue reactivity in response to negative emotions in AN, and the opposite pattern for BN. Furthermore, we explored subgroup differences (restrictive vs. binge-purging AN; history of AN in BN).

METHOD

Patients with AN (n = 41), BN (n = 39), and matched controls (n = 70) completed an emotional eating questionnaire. In a laboratory experiment, we induced negative emotions and measured food cue reactivity (pleasantness, desire to eat (DTE), and corrugator muscle activity).

RESULTS

AN reported emotional undereating, while BN reported emotional overeating. In the laboratory task, BN showed increased DTE and an appetitive corrugator response during negative emotions, selectively towards high-calorie foods. AN showed generalized reduced cue reactivity to high-calorie food regardless of emotional state. This pattern appears to be characteristic of restrictive AN, while cue reactivity of both BN subgroups pointed towards emotional overeating.

CONCLUSIONS

The emotional over- versus undereating framework might help to explain bingeing and restricting along the anorectic-bulimic disorder spectrum, which calls for novel transdiagnostic theories and subgroup-specific treatments.

No effect of very brief exposure to masked food pictures on fear of food in anorexia nervosa

OBJECTIVE

Very brief exposure to masked images of spider stimuli can facilitate approach behaviour towards spiders in fearful subjects. We hypothesized that a similar effect might occur for fear of food in patients with anorexia nervosa (AN), possibly offering a new treatment approach, with advantages over other methods of food exposure.

METHODS

Patients with AN (n = 60) were randomly assigned to one of three experimental conditions and received a single session of exposure to either masked and very briefly presented food images, clearly visible food images, or masked non-food images (i.e. household items). Effects of the three exposure conditions on fear of food and food avoidance were examined.

RESULTS

Contrary to our expectations, very brief food cue exposure was not superior to the control conditions regarding fear of food and approach behaviour towards food immediately after the intervention and body mass index four weeks later.

CONCLUSION

This finding suggests important differences between fear of food in AN and specific phobias such as fear of spiders. The absence of an effect reveals limitations of the very brief exposure method, which might be better suited for evolutionarily relevant threat stimuli.

Increased early motivational response to food in adolescent anorexia nervosa revealed by magnetoencephalography

BACKGROUND

It remains unclear to what extent reduced nutritional intake in anorexia nervosa (AN) is a consequence of a reduced motivational response to food. Although self-reports typically suggest AN patients have a reduced appetitive response, behavioral and neurophysiological measures have revealed evidence for both increased and reduced attentional biases towards food stimuli. The mechanisms influencing food perception in AN, might be clarified using time-sensitive magnetoencephalography (MEG) to differentiate the early (more automatic processing) stages from the late (more controlled) stages.

METHODS

MEG was recorded in 22 partially weight-restored adolescent AN patients and 29 age- and gender-matched healthy control (HC) participants during a rapid serial visual presentation paradigm using 100 high-calorie food, 100 low-calorie food, and 100 non-food pictures. Neural sources of event-related fields were estimated using the L2-Minimum-Norm method and analyzed in early (50-300 ms) and late (350-500 ms) time intervals.

RESULTS

AN patients rated high-calorie food as less palatable and reported overall less food craving than HC participants. Nevertheless, in response to food pictures AN patients showed relative increased neural activity in the left occipito-temporal and inferior frontal regions in the early time interval. No group differences occurred in the late time interval.

CONCLUSIONS

MEG results speak against an overall reduced motivational response to food in AN. Instead, relative increased early food processing in the visual cortex suggests greater motivated attention. A greater appetitive response to food might be an adaptive mechanism in a state of undernourishment. Yet, this relative increased food processing in AN was no longer present later, arguably reflecting rapid downregulation.

Emotional imagination of negative situations: Functional neuroimaging in anorexia and bulimia

Aim

The present study aims to extend the knowledge of the neural correlates of emotion processing in first episode subjects affected by anorexia nervosa (AN) or bulimia nervosa (BN). We applied an emotional distress paradigm targeting negative emotions thought to be relevant for interpersonal difficulties and therapeutic resistance mechanisms.

Methods

The current study applied to 44 female participants with newly diagnosed AN or BN and 20 matched controls a neuroimaging paradigm eliciting affective responses. The measurements also included an extensive assessment comprising clinical scales, neuropsychological tests, measures of emotion processing and empathy.

Results

AN and BN did not differ from controls in terms of emotional response, emotion matching, self-reported empathy and cognitive performance. However, eating disorder and psychopathological clinical scores, as well as alexithymia levels, were increased in AN and BN. On a neural level, no significant group differences emerged, even when focusing on a region of interest selected a priori: the amygdala. Some interesting findings put in relation the hippocampal activity with the level of Body Dissatisfaction of the participants, the relative importance of the key nodes for the common network in the decoding of different emotions (BN = right amygdala, AN = anterior cingulate area), and the qualitative profile of the deactivations.

Conclusions

Our data do not support the hypothesis that participants with AN or BN display reduced emotional responsiveness. However, peculiar characteristics in emotion processing could be associated to the three different groups. Therefore, relational difficulties in eating disorders, as well as therapeutic resistance, could be not secondary to a simple difficulty in feeling and identifying basic negative emotions in AN and BN participants.

The song of Anorexia Nervosa: a specific evoked potential response to musical stimuli in affected participants

PURPOSE

Research applying electroencephalography (EEG) to Anorexia Nervosa (AN) is still limited, even though in other psychiatric disorders EEG has permitted to find out the hallmarks of the disorder. The aim of the study was to explore whether EEG basal activity and reactivity to musical stimulation differ in participants with AN as compared to healthy subjects (HS).

METHODS

Twenty female participants (respectively 10 with AN and 10 healthy controls) were administered a battery of psychometric tests and underwent EEG under three different conditions: (1) at baseline; (2) after a generic music stimulation; and (3) after a favorite musical stimulation.

RESULTS

In participants with AN, basal EEG showed the higher absolute amplitude of cortical slow waves (theta) in the parieto-occipital and temporal derivations, with a deficit in the beta band. In AN, there was a higher N100 latency and a reduced P300 latency compared to HS. While the N100 and P300 latencies were sensitive to the musical stimulus in HS, there was no difference after music stimulation in AN.

CONCLUSION

These data suggest that AN is accompanied by a state of brain hyperarousal with abnormal reactivity to environmental stimuli, similar to the state of HS after musical stimulation. If confirmed, this finding may have treatment implications.

LEVEL OF EVIDENCE

III, Evidence obtained from well-designed cohort or case-control analytic studies.

Modulation of neural fMRI responses to visual food cues by overeating and fasting interventions: A preliminary study

Neural processing of visual food stimuli is perturbated at extremes of weight. Human fMRI studies investigating diet effects on neural processing of food cues could aid in understanding altered brain activation in conditions of under- and overnutrition. In this preliminary study, we examined brain activity changes in response to 10 days of high-calorie-diet (HCD), followed by 10 days of fasting, hypothesizing that HCD would decrease activation in homeostatic and reward regions, while fasting would increase activation in homeostatic/reward regions and decrease activation of self-control regions. Seven adults completed fMRI scanning during a food-cue paradigm (high- and low-calorie food images and nonfood objects), pre- and post-10-day HCD. Six adults completed fMRI scanning pre- and post-10-day fasting. BOLD response changes for contrasts of interest pre- versus post-intervention in regions of interest were examined (peak-level significance set at p(FWE)<0.05). BMI increased by 6.8% and decreased by 8.1% following HCD and fasting, respectively. Following HCD, BOLD response in the hypothalamus (homeostatic control), was attenuated at trend level in response to high- versus low-calorie foods. Following fasting, BOLD response to food versus objects in inhibitory-control areas (dorsolateral prefrontal cortex) was reduced, whereas the activation of homeostatic (hypothalamus), gustatory, and reward brain areas (anterior insula and orbitofrontal cortex) increased. Overfeeding and fasting for 10 days modulate brain activity in response to food stimuli, suggesting that in healthy adults, changes in energy balance affect saliency and reward value of food cues. Future studies are required to understand this interaction in states of unhealthy weight.

Exploring Neural Mechanisms Related to Cognitive Control, Reward, and Affect in Eating Disorders: A Narrative Review of FMRI Studies

Studies using functional magnetic resonance imaging (fMRI) have contributed to our understanding of possible neural abnormalities among individuals with eating disorders. Many of these studies have focused on three domains: 1) cognitive control, 2) reward processing, and 3) affective processing. This review attempts to summarize the recent fMRI findings across these domains among the most well-characterized eating disorders: anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED). Though the literature is a bit murky, a few major themes have emerged. Cognitive control systems are affected among individuals across eating disorder diagnoses, but effects seem least pronounced in AN. Specifically, individuals with all eating disorders appear to show decreased prefrontal activation during cognitive control, but there is less evidence in AN linking decreased prefrontal activation with behavior. There is some evidence that the reinforcing value of food is reduced in AN, but individuals with BN and BED show hyperactivation to rewarding food-related stimuli, suggesting the reinforcing value of food may be enhanced. However, more complex reward processing paradigms show that individuals with BN and BED exhibit hypoactivation to reward anticipation and provide mixed results with regards to reward receipt. There are fewer neuroimaging findings related to affective processing, yet behavioral findings suggest affective processing is important in understanding eating disorders. Though the extant literature is complicated, these studies represent a foundation from which to build and provide insight into potential neurobiological mechanisms that may contribute to the pathophysiology of eating disorders.

Food Folio by Columbia Center for Eating Disorders: A Freely Available Food Image Database

Food images are useful stimuli for the study of cognitive processes as well as eating behavior. To enhance rigor and reproducibility in task-based research, it is advantageous to have stimulus sets that are publicly available and well characterized. Food Folio by Columbia Center for Eating Disorders is a publicly available set of 138 images of Western food items. The set was developed for the study of eating disorders, particularly for use in tasks that capture eating behavior characteristic of these illnesses. It contains foods that are typically eaten, as well as those typically avoided, by individuals with eating disorders. Each image has now been rated across 17 different attributes by a large general United States population sample via Amazon's Mechanical Turk (n = 1054). Ratings included subjective attributes (e.g., tastiness, healthiness, and favorable texture) as well as estimates of nutrient content (e.g., fat and carbohydrate). Each participant rated a subset of stimulus set food items (46 foods) on all 17 dimensions. Additional description of the image set is provided in terms of physical image information and accurate nutritional information. Correlations between subjective ratings were calculated and an exploratory factor analysis and exploratory cluster analysis completed. Outcomes of the factor analysis suggested foods may be described along three latent factors of healthiness, tastiness, and umami taste; the cluster analysis highlighted five distinct clusters of foods varying on these same dimensions. Descriptive outcomes indicated that the stimulus set includes a range of foods that vary along multiple dimensions and thus is likely to be useful in addressing various research questions surrounding eating behavior and cognition in healthy populations, as well as in those with eating disorders. The provision of comprehensive descriptive information allows for stimulus selection that is optimized for a given research question and promotes strong inference.

Implicit and explicit motivational responses to high- and low-calorie food in women with disordered eating

Eating disorders and their symptoms are thought to be associated with altered motivational responding to food. Binge eating may relate to increased reward reactivity, restrictive eating may be associated with increased threat and/or decreased reward reactivity, and the combination of these symptoms within an individual may be linked to motivational conflict to food. Using both implicit (i.e., physiological) and explicit (i.e., self-reported) measures, we tested these hypotheses in 88 women with binge eating only, restrictive eating only, both binge eating and restrictive eating, or no eating pathology. Participants viewed and rated high-calorie food, low-calorie food, and emotional images while startle eye blink and postauricular reflexes were measured. Arousal and craving, but not valence, ratings were significantly greater for high- than low-calorie food. Startle blink reflexes during all food images were significantly lower than during neutral images, whereas only high-calorie foods related to greater postauricular reactivity than neutral images. Eating pathology group did not predict implicit and explicit motivational reactions to food. Exploratory dimensional analyses revealed that rating low-calorie foods as lower on craving predicted endorsement of restrictive eating, while rating low-calorie foods as lower on valence and arousal, and experiencing lower postauricular reactivity to high-calorie foods minus neutral images, predicted greater frequency of restrictive eating episodes. Decreased implicit and explicit appetitive motivation to high- and low-calorie food may relate to the presence and frequency of restrictive eating. Future longitudinal research should investigate whether decreased appetitive responding to food is a risk factor for, versus consequence of, restrictive eating.

How do patients with eating disorders perceive and evaluate food portion sizes? A systematic review

OBJECTIVE

The selection of adequate portion sizes plays a key role in the nutritional treatment of eating disorders (EDs). There is limited knowledge concerning the estimation of portion sizes in individuals with EDs.

METHOD

We performed a systematic review according to the PRISMA statement to synthesise current evidence in this field. Of N = 584 hits, four full-texts were included in the qualitative synthesis.

RESULTS

While patients with anorexia nervosa (AN) tend to overestimate the size of energy-dense food items and small to medium sized meal portions, they do not show a different estimation compared to healthy controls when judging the amount of food pieces. Large portion sizes were associated with increased anxiety in patients with AN.

DISCUSSION

The overestimation of food portion sizes seems to be driven by attitudinal and/or higher cognitive factors associated with AN. Differences between the studies are discussed and suggestions for future studies are given.

Alternative Frameworks for Advancing the Study of Eating Disorders

Eating disorders are life-interrupting psychiatric conditions with high morbidity and mortality, yet the basic mechanisms underlying these conditions are understudied compared with other psychiatric disorders. In this opinion, we suggest that recent knowledge gleaned from genomic and neuroimaging investigations of eating disorders in humans presents a rich opportunity to sharpen animal models of eating disorders and to identify neural mechanisms that contribute to the risk and maintenance of these conditions. Our article reflects the state of the science, with a primary focus on anorexia nervosa (AN) and binge-eating behavior, and encourages further study of all conditions categorized under feeding and eating disorders.

Cognitive improvement following weight gain in patients with anorexia nervosa: A systematic review

OBJECTIVE

Anorexia nervosa (AN) has been associated with cognitive impairment. While re-nutrition is one of the main treatment targets, the effect on cognitive impairments is unclear. The aim of this review was to examine whether cognitive functions improve after weight gain in patients with AN.

METHOD

A systematic review was performed following Preferred Reporting Items for Systematic Reviews and Meta-analyses statement guidelines (PROSPERO CRD42019081993). Literature searches were conducted May 20^th , 2019 in PubMed, EMBASE, PsychINFO and Cochrane Library. Pairs of reviewers screened reports independently based on titles/abstracts (N = 6539) and full texts (N = 378). Furthermore, they assessed the quality of reports, including whether practice effects were accounted for.

RESULTS

Twenty-four longitudinal reports were included featuring 757 patients and 419 healthy controls. Six studies examined children and adolescents. Four out of four studies found processing speed to improve above and beyond what could be assigned to practice effects and three out of four studies found that cognitive flexibility was unaffected after weight gain in children and adolescents. Results from studies of adults were inconclusive.

DISCUSSION

The literature on cognitive change in patients with AN following weight gain is sparse. Preliminary conclusions can be made only for children and adolescents, where weight gain appeared to be associated with improved processing speed.

Visual attention to food cues and the course of anorexia nervosa

Previously, adolescents with anorexia nervosa (AN) showed reduced attentional engagement with food cues compared to adolescents without eating disorder (Jonker, Glashouwer, Hoekzema, Ostafin, & De Jong, 2019). This study tested whether (i) improvement in eating disorder symptoms and BMI are related to an increase in attentional engagement with food, and whether (ii) relatively low attentional engagement is related to persistent AN symptomatology, in the same sample of adolescents with AN (N = 69) from the study of Jonker et al. (2019). Eating disorder symptoms, BMI, and attention for food cues were measured during baseline and at one year follow-up. Adolescents with AN showed a substantial improvement in symptoms and BMI. However, their low attentional engagement with food cues remained unchanged. Change in attentional engagement with food was not related to change in symptoms, nor was low baseline attentional engagement with food predictive of symptom persistence. These findings indicate that improvement in AN symptoms does not seem to require an increase in attentional engagement with food.

A Neglected Topic in Neuroscience: Replicability of fMRI Results With Specific Reference to ANOREXIA NERVOSA

Functional magnetic resonance imaging (fMRI) studies report impaired functional correlates of cognition and emotion in mental disorders. The validity of preexisting studies needs to be confirmed through replication studies, which there is a lack of. So far, most replication studies have been conducted on non-patients (NP) and primarily investigated cognitive and motor tasks. To fill this gap, we conducted the first fMRI replication study to investigate brain function using disease-related food stimuli in patients with anorexia nervosa (AN). Using fMRI, we investigated 31 AN patients and 27 NP for increased amygdala and reduced midcingulate activation when viewing food and non-food stimuli, as reported by the original study (11AN, 11NP; Joos et al., 2011). Similar to the previous study, we observed in the within group comparisons (food>non-food) a frontoinsular activation for both groups. Although in AN the recorded activation clustered more prominently and extended into the cingulate cortex. In the between-group comparisons, the increased amygdala and reduced midcingulate activation could not be replicated. Instead, AN showed a higher activation of the cingulate cortices, the pre-/postcentral gyrus and the inferior parietal lobe. Unlike in the initial study, no significant differences between NP>AN could be observed. The inconsistency of results and the non-replication of the study could have several reasons, such as high inter-individual variance of functional correlates of emotion processing, as well as intra-individual variances and the smaller group size of the initial study. These results underline the importance of replication for assessing the reliability and validity of results from fMRI research.

Multi-method assessment of palatable food exposure in women with and without eating disorders

OBJECTIVE

Eating disorders (EDs) are characterized by dysregulated responses to palatable food. Using a multi-method approach, this study examined responses to palatable food exposure and subsequent ad libitum eating in women with binge-eating disorder (BED: n = 64), anorexia nervosa (AN: n = 16), and bulimia nervosa (BN: n = 35) and 26 healthy controls (HCs).

METHOD

Participants were exposed to palatable food followed by an ad libitum eating opportunity. Affective and psychophysiological responses were measured before and during the task.

RESULTS

Participants with EDs reported greater negative affect, particularly fear, following the food cue exposure, whereas HCs reported no change. BN and BED groups reported greater urge to binge after the food cue exposure, whereas AN and HC groups reported no change. Respiratory sinus arrhythmia levels, skin conductance and tonic skin conductance levels increased during food exposure for all groups. Across baseline and during the food exposure, the BED group had lower respiratory sinus arrhythmia levels relative to the BN and HC groups. The BED group consumed significantly more palatable food than the AN group.

CONCLUSIONS

'Palatable' food stimuli elicited more negative affect, particularly fear, in individuals with EDs; and this, rather than psychophysiological responses, distinguishes individuals with EDs from those without.

Neural Insensitivity to the Effects of Hunger in Women Remitted From Anorexia Nervosa

OBJECTIVE

Anorexia nervosa has the highest mortality rate of any psychiatric condition, yet the pathophysiology of this disorder and its primary symptom, extreme dietary restriction, remains poorly understood. In states of hunger relative to satiety, the rewarding value of food stimuli normally increases to promote eating, yet individuals with anorexia nervosa avoid food despite emaciation. This study's aim was to examine potential neural insensitivity to these effects of hunger in anorexia nervosa.

METHODS

At two scanning sessions scheduled 24 hours apart, one after a 16-hour fast and one after a standardized meal, 26 women who were in remission from anorexia nervosa (to avoid the confounding effects of malnutrition) and 22 matched control women received tastes of sucrose solution or ionic water while functional MRI data were acquired. Within a network of interest responsible for food valuation and transforming taste signals into motivation to eat, the authors compared groups across conditions on blood-oxygen-level-dependent (BOLD) signal and task-based functional connectivity.

RESULTS

Participants in the two groups had similar BOLD responses to sucrose and water tastants. A group-by-condition interaction in the ventral caudal putamen indicated that hunger had opposite effects on tastant response in the control group and the remitted anorexia nervosa group, with an increase and a decrease, respectively, in BOLD response when hungry. Hunger had a similar opposite effect on insula-to-ventral caudal putamen functional connectivity in the remitted anorexia nervosa group compared with the control group. Exploratory analyses indicated that lower caudate response to tastants when hungry was associated with higher scores on harm avoidance among participants in the remitted anorexia nervosa group.

CONCLUSIONS

Reduced recruitment of neural circuitry that translates taste stimulation to motivated eating behavior when hungry may facilitate food avoidance and prolonged periods of extremely restricted food intake in anorexia nervosa.

A systematic and methodological review of attentional biases in eating disorders: Food, body, and perfectionism

OBJECTIVE

The current systematic and methodological review aimed to critically review existing literature utilizing implicit processing, or automatic approach- and/or avoidance-related attentional biases between eating disorder (ED) and nonclinical samples, which (a) highlights how psychophysiological methods advance knowledge of ED implicit bias; (b) explains how findings fit into transdiagnostic versus disorder-specific ED frameworks; and (c) suggests how research can address perfectionism-related ED biases.

METHOD

Three databases were systematically searched to identify studies: PubMed, Scopus, and PsychInfo electronic databases. Peer-reviewed studies of 18- to 39-year-olds with both clinical ED and healthy samples assessing visual attentional biases using pictorial and/or linguistic stimuli related to food, body, and/or perfectionism were included.

RESULTS

Forty-six studies were included. While behavioral results were often similar across ED diagnoses, studies incorporating psychophysiological measures often revealed disease-specific attentional biases. Specifically, women with bulimia nervosa (BN) tend to approach food and other body types, whereas women with anorexia nervosa (AN) tend to avoid food as well as overweight bodies.

CONCLUSIONS

Further integration of psychophysiological and behavioral methods may identify subtle processing variations in ED, which may guide prevention strategies and interventions, and provide important clinical implications. Few implicit bias studies include male participants, investigate binge-eating disorder, or evaluate perfectionism-relevant stimuli, despite the fact that perfectionism is implicated in models of ED.

Functional connectivity underlying hedonic response to food in female adolescents with atypical AN: the role of somatosensory and salience networks

Atypical anorexia nervosa (AN) usually occurs during adolescence. Patients are often in the normal-weight range at diagnosis; however, they often present with signs of medical complications and severe restraint over eating, body dissatisfaction, and low self-esteem. We investigated functional circuitry underlying the hedonic response in 28 female adolescent patients diagnosed with atypical AN and 33 healthy controls. Participants were shown images of food with high (HC) or low (LC) caloric content in alternating blocks during functional MRI. The HC > LC contrast was calculated. Based on the previous literature on full-threshold AN, we hypothesized that patients would exhibit increased connectivity in areas involved in sensory processing and bottom-up responses, coupled to increased connectivity from areas related to top-down inhibitory control, compared with controls. Patients showed increased connectivity in pathways related to multimodal somatosensory processing and memory retrieval. The connectivity was on the other hand decreased in patients in salience and attentional networks, and in a wide cerebello-occipital network. Our study was the first investigation of food-related neural response in atypical AN. Our findings support higher somatosensory processing in patients in response to HC food images compared with controls, however HC food was less efficient than LC food in engaging patients' bottom-up salient responses, and was not associated with connectivity increases in inhibitory control regions. These findings suggest that the psychopathological mechanisms underlying food restriction in atypical AN differ from full-threshold AN. Elucidating the mechanisms underlying the development and maintenance of eating behavior in atypical AN might help designing specific treatment strategies.

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.

Neural Processing of Disorder-Related Stimuli in Patients with Anorexia Nervosa: A Narrative Review of Brain Imaging Studies

Abnormalities and alterations in brain function are commonly associated with the etiology and maintenance of anorexia nervosa (AN). Different symptom categories of AN have been correlated with distinct neurobiological patterns in previous studies. The aim of this literature review is to provide a narrative overview of the investigations into neural correlates of disorder-specific stimuli in patients with AN. Although findings vary across studies, a summary of neuroimaging results according to stimulus category allows us to account for methodological differences in experimental paradigms. Based on the available evidence, the following conclusions can be made: (a) the neural processing of visual food cues is characterized by increased top-down control, which enables restrictive eating, (b) increased emotional and reward processing during gustatory stimulation triggers disorder-specific thought patterns, (c) hunger ceases to motivate food foraging but instead reinforces disorder-related behaviors, (d) body image processing is related to increased emotional and hedonic reactions, (e) emotional stimuli provoke increased saliency associated with decreased top-down control and (f) neural hypersensitivity during interoceptive processing reinforces avoidance behavior. Taken together, studies that investigated symptom-specific neural processing have contributed to a better understanding of the underlying mechanisms of AN.

Neural responses to food stimuli among individuals with eating and weight disorders: a systematic review of event-related potentials

A systematic review was conducted to investigate event-related potentials (ERPs) in response to food and non-food stimuli among individuals with eating and weight disorders. Limiting the search to studies that have analysed ERPs relating to motivated attention and inhibitory control, 19 research papers were extracted from a systematic search in PubMed, Ovid, and Web of Science (2000-2018). An enhanced attentional bias towards food over non-food images (as indexed by P3(00) and LPP amplitudes) was evident for all populations. Individuals with binge eating disorder showed an enhanced attentional response to food cues compared to healthy controls. Inhibitory control-related ERP components (N2(00) and P3a) increased during food-specific no-go trials, but did not differentiate overweight from 'healthy' weight groups. The N2 amplitude to food pictures were positively correlated with caloric intake and food craving among individuals with obesity and binge eating disorder, respectively, while P3(00) was sensitive to hunger levels among overweight and obese females. The heterogeneity of stimuli/paradigms adopted, component timescales extracted, ERPs analysed, and data presented has challenged this review's ability to produce a robust synthesis of results. Some recommendations for future research are discussed.

Recent advances in understanding anorexia nervosa

Anorexia nervosa is a complex psychiatric illness associated with food restriction and high mortality. Recent brain research in adolescents and adults with anorexia nervosa has used larger sample sizes compared with earlier studies and tasks that test specific brain circuits. Those studies have produced more robust results and advanced our knowledge of underlying biological mechanisms that may contribute to the development and maintenance of anorexia nervosa. It is now recognized that malnutrition and dehydration lead to dynamic changes in brain structure across the brain, which normalize with weight restoration. Some structural alterations could be trait factors but require replication. Functional brain imaging and behavioral studies have implicated learning-related brain circuits that may contribute to food restriction in anorexia nervosa. Most notably, those circuits involve striatal, insular, and frontal cortical regions that drive learning from reward and punishment, as well as habit learning. Disturbances in those circuits may lead to a vicious cycle that hampers recovery. Other studies have started to explore the neurobiology of interoception or social interaction and whether the connectivity between brain regions is altered in anorexia nervosa. All together, these studies build upon earlier research that indicated neurotransmitter abnormalities in anorexia nervosa and help us develop models of a distinct neurobiology that underlies anorexia nervosa.

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.

Cognitive Neuroscience of Eating Disorders

Anorexia nervosa and bulimia nervosa are characterized by severely restricted intake, binge eating, and compensatory behaviors like self-induced vomiting. The neurobiological underpinnings of these maladaptive behaviors are poorly understood, but the application of cognitive neuroscience and neuroimaging to eating disorders has begun to elucidate their pathophysiology. Specifically, this review focuses on 3 areas that suggest paths forward: reward, cognitive and behavioral control, and decision making. Understanding the brain-based mechanisms that promote and maintain these often chronic symptoms could guide the development of new and more effective treatments.