This paper systematically reviews the literature pertaining to the use of resting-state functional magnetic resonance imaging (rsfMRI) in anorexia nervosa (AN), classifying studies on the basis of different analysis approaches. We followed PRISMA guidelines. Fifteen papers were included, investigating a total of 294 participants with current or past AN and 285 controls. The studies used seed-based, whole-brain independent component analysis (ICA), network-of-interest ICA based and graph analysis approaches. The studies showed relatively consistent overlap in results, yet little overlap in their analytical approach and/or a-priori assumptions. Functional connectivity alterations were mainly found in the corticolimbic circuitry, involved in cognitive control and visual and homeostatic integration. Some overlapping findings were found in brain areas putatively important in AN, such as the insula. These results suggest altered functional connectivity in networks/areas linked to the main symptom domains of AN, such as impaired cognitive control and body image disturbances. These preliminary evidences suggest that more targeted treatments need to be developed that focus on these two symptom domains. Further studies with multi-approach analyses and longitudinal designs are needed to better understand the complexity of AN.

In his recent paper "Distorted body representations in anorexia nervosa" Gadsby (2017) discussed empirical evidence regarding anorexic patients' distorted body representations. In particular, he interpreted them using the O'Shaughnessy's long-term body image (LTB) hypothesis (O'Shaughnessy, 1998): individuals with anorexia nervosa (AN) have a distorted LTB that tracks changes in the spatial content of the body and supplies this distorted content to other body representations. Even if we agree on the involvement of body memory in the distorted body representation, an open issue not fully addressed in the paper is: why AN patients do not update their LTBs to reflect their true dimensions? Our correspondence tries to answer to this question using a new neuropsychological and neurobiological theory: the Allocentric Lock Theory - ALT.

Anorexia nervosa (AN) is an eating disorder often occurring in adolescence. AN has one of the highest mortality rates amongst psychiatric illnesses and is associated with medical complications and high risk for psychiatric comorbidities, persisting after treatment. Remission rates range from 23% to 33%. Moreover, weight recovery does not necessarily reflect cognitive recovery. This issue is of particular interest in adolescence, characterized by progressive changes in brain structure and functional circuitries, and fast cognitive development. We reviewed existing literature on fMRI studies in adolescents diagnosed with AN, following PRISMA guidelines. Eligible studies had to: (1) be written in English; (2) include only adolescent participants; and (3) use block-design fMRI. We propose a pathogenic model based on normal and AN-related neural and cognitive maturation during adolescence. We propose that underweight and delayed puberty—caused by genetic, environmental, and neurobehavioral factors—can affect brain and cognitive development and lead to impaired cognitive flexibility, which in turn sustains the perpetuation of aberrant behaviors in a vicious cycle. Moreover, greater punishment sensitivity causes a shift toward punishment-based learning, leading to greater anxiety and ultimately to excessive reappraisal over emotions. Treatments combining physiological and neurobehavioral rationales must be adopted to improve outcomes and prevent relapses.

To date, few functional magnetic resonance imaging (fMRI) studies have explored resting-state functional connectivity (RSFC) in long-lasting anorexia nervosa (AN) patients via graph analysis. The aim of the present study is to investigate, via a graph approach (i.e., the network-based statistic), RSFC in a sample of adolescents at the earliest stages of AN (i.e., AN duration less than 6 months). Resting-state fMRI data was obtained from 15 treatment-naive female adolescents with AN restrictive type (AN-r) in its earliest stages and 15 age-matched healthy female controls. A network-based statistic analysis was used to isolate networks of interconnected nodes that differ between the two groups. Group comparison showed a decreased connectivity in a sub-network of connections encompassing the left and right rostral ACC, left paracentral lobule, left cerebellum (10th sub-division), left posterior insula, left medial fronto-orbital gyrus, and right superior occipital gyrus in AN patients. Results were not associated to alterations in intranodal or global connectivity. No sub-networks with an increased connectivity were identified in AN patients. Our findings suggest that RSFC may be specifically affected at the earliest stages of AN. Considering that the altered sub-network comprises areas mainly involved in somatosensory and interoceptive information and processing and in emotional processes, it could sustain abnormal integration of somatosensory and homeostatic signals, which may explain body image disturbances in AN. Further studies with larger samples and longitudinal designs are needed to confirm our findings and better understand the role and consequences of such functional alterations in AN.

Background: Anorexia nervosa and bulimia nervosa are complex mental disorders, and their etiology is still not fully understood. This paper reviews the literature on diffusion tensor imaging studies in patients with anorexia nervosa and bulimia nervosa to explore the usefulness of white matter microstructural analysis in understanding the pathophysiology of eating disorders. Methods: We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to identify diffusion tensor imaging studies that compared patients with an eating disorder to control groups. We searched relevant databases for studies published from database inception to August 2018, using combinations of select keywords. We categorized white matter tracts according to their 3 main classes: projection (i.e., thalamo–cortical), association (i.e., occipital–parietal–temporal–frontal) and commissural (e.g., corpus callosum). Results: We included 19 papers that investigated a total of 427 participants with current or previous eating disorders and 444 controls. Overall, the studies used different diffusion tensor imaging approaches and showed widespread white matter abnormalities in patients with eating disorders. Despite differences among the studies, patients with anorexia nervosa showed mainly white matter microstructural abnormalities of thalamo–cortical tracts (i.e., corona radiata, thalamic radiations) and occipital–parietal–temporal–frontal tracts (i.e., left superior longitudinal and inferior fronto-occipital fasciculi). It was less clear whether white matter alterations persist after recovery from anorexia nervosa. Available data on bulimia nervosa were partially similar to those for anorexia nervosa. Limitations: Study sample composition and diffusion tensor imaging analysis techniques were heterogeneous. The number of studies on bulimia nervosa was too limited to be conclusive. Conclusion: White matter microstructure appears to be affected in anorexia nervosa, and these alterations may play a role in the pathophysiology of this eating disorder. Although we found white matter alterations in bulimia nervosa that were similar to those in anorexia nervosa, white matter changes in bulimia nervosa remain poorly investigated, and these findings were less conclusive. Further studies with longitudinal designs and multi-approach analyses are needed to better understand the role of white matter changes in eating disorders.