Functional and effective connectivity of anterior insula in anorexia nervosa and bulimia nervosa

Associations between neural correlates of visual stimulus processing and set-shifting in ill and recovered women with anorexia nervosa

Women ill with anorexia nervosa (AN) have been shown to exhibit altered cognitive functioning, particularly poor set-shifting (SS). In this study, we investigated whether brain activation in frontal and parietal regions during visual stimulus processing correlates with SS ability. Women currently ill with AN (AN; N=14), recovered women (REC; N=14) and healthy controls (HC; N=15), viewed alternating blocks of food and non-food pictures during functional magnetic resonance imaging (fMRI). The Berg's Card Sorting Task was completed outside the scanner to measure SS. A priori regions of interest (ROIs) were defined in frontal and parietal regions. The activation during visual stimulus processing in several ROIs correlated positively with poor SS ability in REC, particularly in the left dorsal anterior cingulate cortex (dACC). The correlations with poor SS ability were opposite in AN patients, particularly in the right dACC. These findings underscore that addressing heightened levels of cognitive control associated with higher frontal activation could reduce cognitive inflexibility in recovered women. In AN, greater activation in frontal and parietal regions might be necessary to perform at normal levels during various tasks. Thus, weight restoration could be necessary for AN patients prior to addressing cognitive inflexibility.

Enhanced Early Neuronal Processing of Food Pictures in Anorexia Nervosa: A Magnetoencephalography Study

Neuroimaging studies in Anorexia Nervosa (AN) have shown increased activation in reward and cognitive control regions in response to food, and a behavioral attentional bias (AB) towards food stimuli is reported. This study aimed to further investigate the neural processing of food using magnetoencephalography (MEG). Participants were 13 females with restricting-type AN, 14 females recovered from restricting-type AN, and 15 female healthy controls. MEG data was acquired whilst participants viewed high- and low-calorie food pictures. Attention was assessed with a reaction time task and eye tracking. Time-series analysis suggested increased neural activity in response to both calorie conditions in the AN groups, consistent with an early AB. Increased activity was observed at 150 ms in the current AN group. Neuronal activity at this latency was at normal level in the recovered group; however, this group exhibited enhanced activity at 320 ms after stimulus. Consistent with previous studies, analysis in source space and behavioral data suggested enhanced attention and cognitive control processes in response to food stimuli in AN. This may enable avoidance of salient food stimuli and maintenance of dietary restraint in AN. A later latency of increased activity in the recovered group may reflect a reversal of this avoidance, with source space and behavioral data indicating increased visual and cognitive processing of food stimuli.

Alterations in emotion generation and regulation neurocircuitry in depression and eating disorders: A comparative review of structural and functional neuroimaging studies

Major depression and eating disorders (EDs) are highly co-morbid and may share liability. Impaired emotion regulation may represent a common etiological or maintaining mechanism. Research has demonstrated that depressed individuals and individuals with EDs exhibit impaired emotion regulation, with these impairments being associated with changes in brain structure and function. The goal of this review was to evaluate findings from neuroimaging studies of depression and EDs to determine whether there are overlapping alterations in the brain regions known to be involved in emotion regulation, evidence of which would aid in the diagnosis and treatment of these conditions. Our review of the literature suggests that depression and EDs exhibit common structural and functional alterations in brain regions involved in emotion regulation, including the amygdala, ventral striatum and nucleus accumbens, anterior cingulate cortex, insula, and dorsolateral prefrontal cortex. We present preliminary support for a shared etiological mechanism. Future studies should consider manipulating emotion regulation in a sample of individuals with depression and EDs to better characterize abnormalities in these brain circuits.

Brain parcellation choice affects disease-related topology differences increasingly from global to local network levels

Network-based analyses of deviant brain function have become extremely popular in psychiatric neuroimaging. Underpinning brain network analyses is the selection of appropriate regions of interest (ROIs). Although ROI selection is fundamental in network analysis, its impact on detecting disease effects remains unclear. We investigated the impact of parcellation choice when comparing results from different studies. We investigated the effects of anatomical (AAL) and literature-based (Dosenbach) parcellation schemes on comparability of group differences in 35 female patients with anorexia nervosa and 35 age- and sex-matched healthy controls. Global and local network properties, including network-based statistics (NBS), were assessed on resting state functional magnetic resonance imaging data obtained at 3T. Parcellation schemes were comparably consistent on global network properties, while NBS and local metrics differed in location, but not metric type. Location of local metric alterations varied for AAL (parietal and cingulate cortices) versus Dosenbach (insula, thalamus) parcellation approaches. However, consistency was observed for the occipital cortex. Patient-specific global network properties can be robustly observed using different parcellation schemes, while graph metrics characterizing impairments of individual nodes vary considerably. Therefore, the impact of parcellation choice on specific group differences varies depending on the level of network organization.

A debate on working memory and cognitive control: can we learn about the treatment of substance use disorders from the neural correlates of anorexia nervosa?

BACKGROUND

Anorexia Nervosa (AN) is a debilitating, sometimes fatal eating disorder (ED) whereby restraint of appetite and emotion is concomitant with an inflexible, attention-to-detail perfectionist cognitive style and obsessive-compulsive behaviour. Intriguingly, people with AN are less likely to engage in substance use, whereas those who suffer from an ED with a bingeing component are more vulnerable to substance use disorder (SUD).

DISCUSSION

This insight into a beneficial consequence of appetite control in those with AN, which is shrouded by the many other unhealthy, excessive and deficit symptoms, may provide some clues as to how the brain could be trained to exert better, sustained control over appetitive and impulsive processes. Structural and functional brain imaging studies implicate the executive control network (ECN) and the salience network (SN) in the neuropathology of AN and SUD. Additionally, excessive employment of working memory (WM), alongside more prominent cognitive deficits may be utilised to cope with the experience of negative emotions and may account for aberrant brain function. WM enables mental rehearsal of cognitive strategies while regulating, restricting or avoiding neural responses associated with the SN. Therefore, high versus low WM capacity may be one of the factors that unites common cognitive and behavioural symptoms in those suffering from AN and SUD respectively. Furthermore, emerging evidence suggests that by evoking neural plasticity in the ECN and SN with WM training, improvements in neurocognitive function and cognitive control can be achieved. Thus, considering the neurocognitive processes of excessive appetite control and how it links to WM in AN may aid the application of adjunctive treatment for SUD.

Abnormal functional global and local brain connectivity in female patients with anorexia nervosa

BACKGROUND

Previous resting-state functional connectivity studies in patients with anorexia nervosa used independent component analysis or seed-based connectivity analysis to probe specific brain networks. Instead, modelling the entire brain as a complex network allows determination of graph-theoretical metrics, which describe global and local properties of how brain networks are organized and how they interact.

METHODS

To determine differences in network properties between female patients with acute anorexia nervosa and pairwise matched healthy controls, we used resting-state fMRI and computed well-established global and local graph metrics across a range of network densities.

RESULTS

Our analyses included 35 patients and 35 controls. We found that the global functional network structure in patients with anorexia nervosa is characterized by increases in both characteristic path length (longer average routes between nodes) and assortativity (more nodes with a similar connectedness link together). Accordingly, we found locally decreased connectivity strength and increased path length in the posterior insula and thalamus.

LIMITATIONS

The present results may be limited to the methods applied during preprocessing and network construction.

CONCLUSION

We demonstrated anorexia nervosa-related changes in the network configuration for, to our knowledge, the first time using resting-state fMRI and graph-theoretical measures. Our findings revealed an altered global brain network architecture accompanied by local degradations indicating wide-scale disturbance in information flow across brain networks in patients with acute anorexia nervosa. Reduced local network efficiency in the thalamus and posterior insula may reflect a mechanism that helps explain the impaired integration of visuospatial and homeostatic signals in patients with this disorder, which is thought to be linked to abnormal representations of body size and hunger.

Functional connectivity for face processing in individuals with body dysmorphic disorder and anorexia nervosa

BACKGROUND

Body dysmorphic disorder (BDD) and anorexia nervosa (AN) are both characterized by distorted perception of appearance. Previous studies in BDD suggest abnormalities in visual processing of own and others' faces, but no study has examined visual processing of faces in AN, nor directly compared the two disorders in this respect.

METHOD

We collected functional magnetic resonance imaging data on 60 individuals of equivalent age and gender in each of three groups--20 BDD, 20 weight-restored AN, and 20 healthy controls (HC)--while they viewed images of others' faces that contained only high or low spatial frequency information (HSF or LSF). We tested hypotheses about functional connectivity within specialized sub-networks for HSF and LSF visual processing, using psychophysiological interaction analyses.

RESULTS

The BDD group demonstrated increased functional connectivity compared to HC between left anterior occipital face area and right fusiform face area (FFA) for LSF faces, which was associated with symptom severity. Both BDD and AN groups had increased connectivity compared to HC between FFA and precuneous/posterior cingulate gyrus for LSF faces, and decreased connectivity between FFA and insula. In addition, we found that LSF connectivity between FFA and posterior cingulate gyrus was significantly associated with thoughts about own appearance in AN.

CONCLUSIONS

Results suggest similar abnormal functional connectivity within higher-order systems for face processing in BDD and AN, but distinct abnormal connectivity patterns within occipito-temporal visual networks. Findings may have implications for understanding relationships between these disorders, and the pathophysiology underlying perceptual distortions.

Anorexia nervosa

Anorexia nervosa (AN) is a psychiatric condition characterized by severe weight loss and secondary problems associated with malnutrition. AN predominantly develops in adolescence in the peripubertal period. Without early effective treatment, the course is protracted with physical, psychological and social morbidity and high mortality. Despite these effects, patients are noted to value the beliefs and behaviours that contribute to their illness rather than regarding them as problematic, which interferes with screening, prevention and early intervention. Involving the family to support interventions early in the course of the illness can produce sustained changes; however, those with a severe and/or protracted illness might require inpatient nursing support and/or outpatient psychotherapy. Prevention programmes aim to moderate the overvaluation of 'thinness' and body dissatisfaction as one of the proximal risk factors. The low prevalence of AN limits the ability to identify risk factors and to study the timing and sex distribution of the condition. However, genetic profiles, premorbid features, and brain structures and functions of patients with AN show similarities with other psychiatric disorders and contrast with obesity and metabolic disorders. Such studies are informing approaches to address the neuroadaptation to starvation and the other various physical and psychosocial deficits associated with AN. This Primer describes the epidemiology, diagnosis, screening and prevention, aetiology, treatment and quality of life of patients with AN.

Advances from neuroimaging studies in eating disorders

Over the past decade, brain imaging has helped to better define eating disorder-related brain circuitry. Brain research on gray matter (GM) and white matter (WM) volumes had been inconsistent, possibly due to the effects of acute starvation, exercise, medication, and comorbidity, but newer studies have controlled for such effects. Those studies suggest larger left medial orbitofrontal gyrus rectus volume in ill adult and adolescent anorexia nervosa after recovery from anorexia nervosa, and in adult bulimia nervosa. The orbitofrontal cortex is important in terminating food intake, and altered function could contribute to self-starvation. The right insula, which processes taste but also interoception, was enlarged in ill adult and adolescent anorexia nervosa, as well as adults recovered from the illness. The fixed perception of being fat in anorexia nervosa could be related to altered insula function. A few studies investigated WM integrity, with the most consistent finding of reduced fornix integrity in anorexia and bulimia nervosa-a limbic pathway that is important in emotion but also food intake regulation. Functional brain imaging using basic sweet taste stimuli in eating disorders during the ill state or after recovery implicated repeatedly reward pathways, including insula and striatum. Brain imaging that targeted dopamine-related brain activity using taste-reward conditioning tasks suggested that this circuitry is hypersensitive in anorexia nervosa, but hyporesponsive in bulimia nervosa and obesity. Those results are in line with basic research and suggest adaptive reward system changes in the human brain in response to extremes of food intake-changes that could interfere with normalization of eating behavior.

Altered resting state functional connectivity of anterior cingulate cortex in drug naïve adolescents at the earliest stages of anorexia nervosa

Previous Resting-State Functional Connectivity (RSFC) studies have shown several functional alterations in adults with or recovered from long Anorexia Nervosa (AN). The aim of this paper was to investigate whole brain RSFC in adolescents with AN in the earliest stages, less than 6 months, of the disorder. Sixteen drug-naïve outpatient female adolescents with AN-restrictive type (AN-r) (mean age: 15,8; SD 1,7) were compared to 16 age-matched healthy female (mean age: 16,3; SD 1,4). Relevant resting state networks (RSNs) were identified using independent component analysis (ICA) from functional magnetic resonance imaging data; a dual regression technique was used to detect between-group differences in the RSNs. Between-group differences of the functional connectivity maps were found in the executive control network (ECN). Particularly, decreased temporal correlation was observed in AN-r patients relative to healthy controls between the ECN functional connectivity maps and the anterior cingulate cortex (p < 0.05 corrected). Our results in AN adolescents may represent an early trait-related biomarker of the disease. Considering that the above mentioned network and its area are mainly involved in cognitive control and emotional processing, our findings could explain the impaired cognitive flexibility in relation to body image and appetite in AN patients.

Recent Advances in Developmental and Risk Factor Research on Eating Disorders

The Diagnostic and Statistical Manual of Mental Disorders (i.e., DSM-5) currently recognizes three primary eating disorders: anorexia nervosa, bulimia nervosa, and binge eating disorder. The origins of eating disorders are complex and remain poorly understood. However, emerging research highlights a dimensional approach to understanding the multifactorial etiology of eating disorders as a means to inform assessment, prevention, and treatment efforts. Guided by research published since 2011, this review summarizes recent findings elucidating risk factors for the development of eating disorders across the lifespan in three primary domains: (1) genetic/biological, (2) psychological, and (3) socio-environmental. Prospective empirical research in clinical samples with full-syndrome eating disorders is emphasized with added support from cross-sectional studies, where relevant. The developmental stages of puberty and the transition from adolescence to young adulthood are discussed as crucial periods for the identification and prevention of eating disorders. The importance of continuing to elucidate the mechanisms underlying gene by environmental interactions in eating disorder risk is also discussed. Finally, controversial topics in the field of eating disorder research and the clinical implications of this research are summarized.

Reduced functional connectivity in the thalamo-insular subnetwork in patients with acute anorexia nervosa

The neural underpinnings of anorexia nervosa (AN) are poorly understood. Results from existing functional brain imaging studies using disorder-relevant food- or body-stimuli have been heterogeneous and may be biased due to varying compliance or strategies of the participants. In this study, resting state functional connectivity imaging was used. To explore the distributed nature and complexity of brain function we characterized network patterns in patients with acute AN. Thirty-five unmedicated female acute AN patients and 35 closely matched healthy female participants underwent resting state functional magnetic resonance imaging. We used a network-based statistic (NBS) approach [Zalesky et al., 2010a] to identify differences between groups by isolating a network of interconnected nodes with a deviant connectivity pattern. Group comparison revealed a subnetwork of connections with decreased connectivity including the amygdala, thalamus, fusiform gyrus, putamen and the posterior insula as the central hub in the patient group. Results were not driven by changes in intranodal or global connectivity. No network could be identified where AN patients had increased coupling. Given the known involvement of the identified thalamo-insular subnetwork in interoception, decreased connectivity in AN patients in these nodes might reflect changes in the propagation of sensations that alert the organism to urgent homeostatic imbalances and pain-processes that are known to be severely disturbed in AN and might explain the striking discrepancy between patient's actual and perceived internal body state.

Are Extremes of Consumption in Eating Disorders Related to an Altered Balance between Reward and Inhibition?

The primary defining characteristic of a diagnosis of an eating disorder (ED) is the "disturbance of eating or eating-related behavior that results in the altered consumption or absorption of food" (DSM V; American Psychiatric Association, 2013). There is a spectrum, ranging from those who severely restrict eating and become emaciated on one end to those who binge and overconsume, usually accompanied by some form of compensatory behaviors, on the other. How can we understand reasons for such extremes of food consummatory behaviors? Recent work on obesity and substance use disorders has identified behaviors and neural pathways that play a powerful role in human consummatory behaviors. That is, corticostriatal limbic and dorsal cognitive neural circuitry can make drugs and food rewarding, but also engage self-control mechanisms that may inhibit their use. Importantly, there is considerable evidence that alterations of these systems also occur in ED. This paper explores the hypothesis that an altered balance of reward and inhibition contributes to altered extremes of response to salient stimuli, such as food. We will review recent studies that show altered sensitivity to reward and punishment in ED, with evidence of altered activity in corticostriatal and insula processes with respect to monetary gains or losses, and tastes of palatable foods. We will also discuss evidence for a spectrum of extremes of inhibition and dysregulation behaviors in ED supported by studies suggesting that this is related to top-down self-control mechanisms. The lack of a mechanistic understanding of ED has thwarted efforts for evidence-based approaches to develop interventions. Understanding how ED behavior is encoded in neural circuits would provide a foundation for developing more specific and effective treatment approaches.

Stress- and PTSD-associated obesity and metabolic dysfunction: a growing problem requiring further research and novel treatments

Posttraumatic stress disorder (PTSD) is a growing public health concern. More recently, evidence has indicated that PTSD leads to obesity and associated metabolic dysfunction. Possible mechanisms of this link are through dysfunction of the hypothalamic-pituitary-adrenal axis and related moderation of appetite hormones and neural activity, leading to changes in consumptive behaviors. Although research has been examining associations between PTSD and obesity, diabetes, cardiovascular disease, and metabolic syndrome, future research should delineate potential mechanisms for these associations and develop targeted treatments to reduce these metabolic outcomes.

Reduced salience and default mode network activity in women with anorexia nervosa

BACKGROUND

The neurobiology of anorexia nervosa is poorly understood. Neuronal networks contributing to action selection, self-regulation and interoception could contribute to pathologic eating and body perception in people with anorexia nervosa. We tested the hypothesis that the salience network (SN) and default mode network (DMN) would show decreased intrinsic activity in women with anorexia nervosa and those who had recovered from the disease compared to controls. The basal ganglia (BGN) and sensorimotor networks (SMN) were also investigated.

METHODS

Between January 2008 and January 2012, women with restricting-type anorexia nervosa, women who recovered from the disease and healthy control women completed functional magnetic resonance imaging during a conditioned stimulus task. Network activity was studied using independent component analysis.

RESULTS

We studied 20 women with anorexia nervosa, 24 recovered women and 24 controls. Salience network activity in the anterior cingulate cortex was reduced in women with anorexia nervosa (p = 0.030; all results false-discovery rate- corrected) and recovered women (p = 0.039) compared to controls. Default mode network activity in the precuneus was reduced in women with anorexia compared to controls (p = 0.023). Sensorimotor network activity in the supplementary motor area (SMA; p = 0.008), and the left (p = 0.028) and right (p = 0.002) postcentral gyrus was reduced in women with anorexia compared to controls; SMN activity in the SMA (p = 0.019) and the right postcentral gyrus (p = 0.008) was reduced in women with anorexia compared to recovered women. There were no group differences in the BGN.

LIMITATIONS

Differences between patient and control populations (e.g., depression, anxiety, medication) are potential confounds, but were included as covariates.

CONCLUSION

Reduced SN activity in women with anorexia nervosa and recovered women could be a trait-related biomarker or illness remnant, altering the drive to approach food. The alterations in the DMN and SMN observed only in women with anorexia nervosa suggest state-dependent abnormalities that could be related to altered interoception and body image in these women when they are underweight but that remit following recovery.

Aberrant network integrity of the inferior frontal cortex in women with anorexia nervosa

Neuroimaging studies investigating the neural profile of anorexia nervosa (AN) have revealed a predominant imbalance between the reward and inhibition systems of the brain, which are also hallmark characteristics of the disorder. However, little is known whether these changes can also be determined independent of task condition, using resting-state functional magnetic resonance imaging, in currently ill AN patients.

Therefore the aim of our study was to investigate resting-state connectivity in AN patients (n = 12) compared to healthy athlete (n = 12) and non-athlete (n = 14) controls. For this purpose, we used degree centrality to investigate functional connectivity of the whole-brain network and then Granger causality to analyze effective connectivity (EC), to understand directional aspects of potential alterations.

We were able to show that the bilateral inferior frontal gyrus (IFG) is a region of special functional importance within the whole-brain network, in AN patients, revealing reduced functional connectivity compared to both healthy control groups. Furthermore, we found decreased EC from the right IFG to the midcingulum and increased EC from the bilateral orbitofrontal gyrus to the right IFG. For the left IFG, we only observed increased EC from the bilateral insula to the left IFG.

These results suggest that AN patients have reduced connectivity within the cognitive control system of the brain and increased connectivity within regions important for salience processing. Due to its fundamental role in inhibitory behavior, including motor response, altered integrity of the inferior frontal cortex could contribute to hyperactivity in AN.

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We evaluate resting-state functional (FC) and effective (EC) connectivity.

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We compare anorexia nervosa (AN) patients with healthy controls.

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AN patients show reduced FC in the inferior frontal gyrus (IFG).

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AN patients show reduced EC from the IFG and increased EC to the IFG.

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Altered FC patterns correlate with physical activity.

The neurobiology of anorexia nervosa: a systematic review

OBJECTIVE

Recent advances in neuroimaging techniques have enabled a better understanding of the neurobiological underpinnings of anorexia nervosa (AN). The aim of this paper was to summarise our current understanding of the neurobiology of AN.

METHODS

The literature was searched using the electronic databases PubMed and Google Scholar, and by additional hand searches through reference lists and specialist eating disorders journals. Relevant studies were included if they were written in English, only used human participants, had a specific AN group, used clinical populations of AN, group comparisons were reported for AN compared to healthy controls and not merely AN compared to other eating disorders or other psychiatric groups, and were not case studies.

RESULTS

The systematic review summarises a number of structural and functional brain differences which are reported in individuals with AN, including differences in neurotransmitter function, regional cerebral blood flow, glucose metabolism, volumetrics and the blood oxygen level dependent response.

CONCLUSION

Several structural and functional differences have been reported in AN, some of which reverse and others which persist following weight restoration. These findings have important implications for our understanding of the neurobiological underpinnings of AN, and further research in this field may provide new direction for the development of more effective treatments.

Resting-state synchrony between anterior cingulate cortex and precuneus relates to body shape concern in anorexia nervosa and bulimia nervosa

Cortical areas supporting cognitive control and salience demonstrate different neural responses to visual food cues in patients with eating disorders. This top-down cognitive control, which interacts with bottom-up appetitive responses, is tightly integrated not only in task conditions but also in the resting-state. The dorsal anterior cingulate cortex (dACC) is a key node of a large-scale network that is involved in self-referential processing and cognitive control. We investigated resting-state functional connectivity of the dACC and hypothesized that altered connectivity would be demonstrated in cortical midline structures involved in self-referential processing and cognitive control. Seed-based resting-state functional connectivity was analyzed in women with anorexia nervosa (N=18), women with bulimia nervosa (N=20) and age matched healthy controls (N=20). Between group comparisons revealed that the anorexia nervosa group exhibited stronger synchronous activity between the dACC and retrosplenial cortex, whereas the bulimia nervosa group showed stronger synchronous activity between the dACC and medial orbitofrontal cortex. Both groups demonstrated stronger synchronous activity between the dACC and precuneus, which correlated with higher scores of the Body Shape Questionnaire. The dACC-precuneus resting-state synchrony might be associated with the disorder-specific rumination on eating, weight and body shape in patients with eating disorders.

Brain responses to body image stimuli but not food are altered in women with bulimia nervosa

BACKGROUND

Research into the neural correlates of bulimia nervosa (BN) psychopathology remains limited.

METHODS

In this functional magnetic resonance imaging study, 21 BN patients and 23 healthy controls (HCs) completed two paradigms: (1) processing of visual food stimuli and (2) comparing their own appearance with that of slim women. Participants also rated food craving and anxiety levels.

RESULTS

Brain activation patterns in response to food cues did not differ between women with and without BN. However, when evaluating themselves against images of slim women, BN patients engaged the insula more and the fusiform gyrus less, compared to HCs, suggesting increased self-focus among women with BN whilst comparing themselves to a 'slim ideal'. In these BN patients, exposure to food and body image stimuli increased self-reported levels of anxiety, but not craving.

CONCLUSIONS

Our findings suggest that women with BN differ from HCs in the way they process body image, but not in the way they process food stimuli.

Prefrontal control of the amygdala during real-time fMRI neurofeedback training of emotion regulation

We observed in a previous study (PLoS ONE 6:e24522) that the self-regulation of amygdala activity via real-time fMRI neurofeedback (rtfMRI-nf) with positive emotion induction was associated, in healthy participants, with an enhancement in the functional connectivity between the left amygdala (LA) and six regions of the prefrontal cortex. These regions included the left rostral anterior cingulate cortex (rACC), bilateral dorsomedial prefrontal cortex (DMPFC), bilateral superior frontal gyrus (SFG), and right medial frontopolar cortex (MFPC). Together with the LA, these six prefrontal regions thus formed the functional neuroanatomical network engaged during the rtfMRI-nf procedure. Here we perform a structural vector autoregression (SVAR) analysis of the effective connectivity for this network. The SVAR analysis demonstrates that the left rACC plays an important role during the rtfMRI-nf training, modulating the LA and the other network regions. According to the analysis, the rtfMRI-nf training leads to a significant enhancement in the time-lagged effect of the left rACC on the LA, potentially consistent with the ipsilateral distribution of the monosynaptic projections between these regions. The training is also accompanied by significant increases in the instantaneous (contemporaneous) effects of the left rACC on four other regions – the bilateral DMPFC, the right MFPC, and the left SFG. The instantaneous effects of the LA on the bilateral DMPFC are also significantly enhanced. Our results are consistent with a broad literature supporting the role of the rACC in emotion processing and regulation. Our exploratory analysis provides, for the first time, insights into the causal relationships within the network of regions engaged during the rtfMRI-nf procedure targeting the amygdala. It suggests that the rACC may constitute a promising target for rtfMRI-nf training along with the amygdala in patients with affective disorders, particularly posttraumatic stress disorder (PTSD).

Advances in the neurobiology of eating disorders

PURPOSE OF REVIEW

To systematize new neurobiological findings on the cause and treatment of eating disorders.

RECENT FINDINGS

The conceptual framework of the cause of eating disorders has undergone great changes in the past decades. Recently, the National Institute of Mental Health proposed a new set of criteria for research purposes--the Research Domain Criteria (RDoC). We aim to structure this study as much as possible using these constructs across biological units of analysis, summarizing new findings. Brain imaging techniques have become sophisticated in identifying brain circuits related to illness behaviour and to fundamental traits such as reward and social processing. Genetic studies have moved from candidate gene studies onto genome-wide association studies; however, the field needs to cooperate to collect larger samples in order to benefit from this approach. Hormonal changes as the results of starvation or as underlying factors for behavioural changes still receive attention in both animal and human studies. Advances made in neuropsychology show problems in cognition (set shifting and central coherence) and in other RDoC domains. Some of these findings have been translated into treatment.

SUMMARY

New biological models are being developed which explain causal and maintaining factors. The RDoC construct may be used to systematize these findings.

Modulation of functionally localized right insular cortex activity using real-time fMRI-based neurofeedback

The capacity for subjects to learn to volitionally control localized brain activity using neurofeedback is actively being investigated. We aimed to investigate the ability of healthy volunteers to quickly learn to use visual feedback during real-time functional MRI (rtfMRI) to modulate brain activity within their anterior right insular cortex (RIC) localized during a blink suppression task, an approach of possible interest in the use of rtfMRI to reduce urges. The RIC region of interest (RIC-ROI) was functionally localized using a blink suppression task, and blood-oxygen level dependent (BOLD) signal changes within RIC-ROI used to create a constantly updating display fed back to the subject in the scanner. Subjects were instructed to use emotional imagery to try and increase activity within RIC-ROI during four feedback training runs (FB1–FB4). A “control” run (CNTRL) before training and a “transfer” run (XSFR) after training were performed without feedback to assess for baseline abilities and learning effects. Fourteen participants completed all neurofeedback training runs. At the group-level, increased BOLD activity was seen in the anterior RIC during all the FB runs, but a significant increase in the functionally defined RIC-ROI was only attained during FB2. In atlas-defined insular cortex ROIs, significant increases were seen bilaterally during the CNTRL, FB1, FB2, and FB4 runs. Increased activity within the insular cortices did not show lateralization. Training did, however, result in a significant increase in functional connectivity between the RIC-ROI and the medial frontal gyrus when comparing FB4 to FB1. Since neurofeedback training did not lead to an increase in BOLD signal across all feedback runs, we suggest that learning to control one’s brain activity in this fashion may require longer or repeated rtfMRI training sessions.

Brain volumetric abnormalities in patients with anorexia and bulimia nervosa: a voxel-based morphometry study

Recent studies focussing on neuroimaging features of eating disorders have observed that anorexia nervosa (AN) is characterized by significant grey matter (GM) atrophy in many brain regions, especially in the cerebellum and anterior cingulate cortex. To date, no studies have found GM atrophy in bulimia nervosa (BN) or have directly compared patients with AN and BN. We used voxel-based morphometry (VBM) to characterize brain abnormalities in AN and BN patients, comparing them with each other and with a control group, and correlating brain volume with clinical features. We recruited 17 AN, 13 BN and 14 healthy controls. All subjects underwent high-resolution magnetic resonance imaging (MRI) with a T1-weighted 3D image. VBM analysis was carried out with the FSL-VBM 4.1 tool. We found no global atrophy, but regional GM reduction in AN with respect to controls and BN in the cerebellum, fusiform area, supplementary motor area, and occipital cortex, and in the caudate in BN compared to AN and controls. Both groups of patients had a volumetric increase bilaterally in somatosensory regions with respect to controls, in areas that are typically involved in the sensory-motor integration of body stimuli and in mental representation of the body image. Our VBM study documented, for the first time in BN patients, the presence of volumetric alterations and replicated previous findings in AN patients. We evidenced morphological differences between AN and BN, demonstrating in the latter atrophy of the caudate nucleus, a region involved in reward mechanisms and processes of self-regulation, perhaps involved in the genesis of the binge-eating behaviors of this disorder.

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.

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.