Body image distortion in anorexia nervosa
In their recent Primer (Anorexia nervosa. Nat. Rev. Dis. Primers 1, 15074 (2015))1, Janet Treasure and colleagues give an impor tant update on the advances made in the aetio logy, assessment, prevention and treat ment of anorexia nervosa (AN) The authors also highlight the need for better, faster and lasting improvements in the management of this 'enigmatic' disorder, which crucially depends on improved understanding of speci fic disease mechanisms. However, in their description, they do not include the consistent evidence that disturbed body image does not only motivate severe dietary restriction and other weight loss behaviours but also plays a central part in the initiation, persistence and relapse of AN2 8. The Primer1 states that the under lying mechanism of the so called body image distortion (BID) in which emaciated individ uals perceive them selves as fat9, remains obscure. Yet, there is widespread agreement that this evidence at both the conceptual and the empirical levels is imperative for elucidating what is behind severe and intense BID2 10. Findings from an increasing number of functional MRI (fMRI) studies, conducted (based on the symptom provocation para digm) over the past 15 years and recently reviewed by one of us7, provide valuable insights into the neural basis of BID in AN. Unfortunately, we felt that these issues were not entirely addressed by the Primer1, making it difficult to understand the 'reasonably consistent' (REF. 7) evidence produced by this research3. The review7 summarized that the 'affective' component of BID in AN is related to alterations of the prefrontal cortex, the insula and the amygdala and that the 'per ceptive' component of BID is related to alter ations of the parietal lobes (which have roles in spatial and body representations4 7,10, body ownership9 12 and other features requiring multisensory integration4 7,11 14) or, more accu rately, the posterior parietal regions (which are involved in visuospatial processing4 7,10,15) A deficit in parietal cortex mediated func tions in AN is also underscored by findings from neurocognitive studies4 6. Although both extant neuroimaging and behavioural data2,4,7,8 suggest that two components of body image (the estimation of one's own body size and the attitude towards one's own body in terms of an emotional evaluation) are disturbed in individ uals with AN, these aspects might have been described in more detail in the Primer1. In fact, although two (widely accepted) body image components can be distinguished, this does not imply that they are independent4,5,15. Indeed, experimental evidence supports a direct (unidirectional) link between how we perceive and how we feel about our body12. The aforementioned specific neural bases of the affective component of BID in AN also sup port an altered emotional response to unpleas ant (for example, self distorted fat image) stimuli7. Furthermore, in the few available fMRI studies based on a word paradigm (that is, tasks using 'fat' 'thin' and 'neutral' words) a variation in amygdala response was absent making the involvement of this brain region less clear but suggesting the greater rele vance of self perception and the mechanism of body image construction5,6,9 (see below) There is the need to take into account these (and other convergent4,5,12,13) clues and the considerable room for improvement that remains from the first line prevention and psychotherapeutic interventions2,3,5,8,10,12,13, currently described in the Primer1 (for example, the Body Project and enhanced cognitive behavioural ther apy) and targeting the 'affective' body image component2,5,10,12,13. Thus, we would suggest that it is now time to consider the develop ment of intervention strategies that target the perceptive component. Cognitive neuroscientific strides in the field of body self consciousness (that is, the experience of being in a body process5, with body ownership being its fundamental con stituent5,11) offer a novel perspective for, if not a paradigm shift in, understanding the mech anism of body image construction5,6,10,11,13,15 only inferred by the already mentioned experimental paradigms used to explore the neural basis of BID in AN4,7. Fundamentally, our spatial experience, including the bodily one, is organized around two different refer ence frames: egocentric, which has its primary source in 'online' representations (referring to the temporal flow of information that constructs how our body is right now) and allocentric, which has its primary source in 'offline' representations (referring to what our body is normally like)5,6,10,13,15. That is, people use both the memory of how the body, includ ing its shape and size, is believed (or remem bered) to be (offline) and the perception of the body 'here and now' (online) to construct their body image5,6. The conceptual distinction between online and offline representations should not imply that these representations of the body are unconnected, as they can and do interact, with the online information about the body being continuously integrating with and compared to the offline model of the body in the brain5,6,10,13,15. Neuroscientifically informed models highlight how a similar process of amending and updating offline representa tions based on new online representations might underline the complex relationship between body image, dietary restriction and weight loss5. From this perspective, individuals who lose large amounts of weight might adapt their offline model of the body accordingly, as the new online information is received and updates the oldest stored model of the body5. Accordingly, an impediment in the transaction between online and offline information might be at play in patients with AN who have a per sistent experience of being fat, even when they are objectively emaciated5. In support, sophis ticated contemporary research10 has shown that individuals with AN in the earliest stages are 'locked' in a virtual 'wrong' body that they detest, which differs from the real one. Despite the importance of these10 (and additional5,13,14) findings and the known role of brain abnormalities in the (posterior pari etal) areas involved in the block of the online offline transformation process5,6,11,15, further research is needed to investigate additional factors (for example, stress) involved in the impaired ability of updating5,10, which were previously linked to food intake reduction in AN10. Some additional hypotheses have been proposed based on research on neuropsycho logical functioning1,4,6,10 in patients with AN but they require specific testing. For example, some evidence suggests that people with AN not only focus on details (weak central coher ence) but they also seem to have an attentional bias towards negatively charged details6. This feature has been suggested to affect both the perception of the body and how it is remem bered6. Another hypothesis states that weak set shifting (that is, reduced mental flexibility as indicated by the ability to move back and forth between tasks) and poor visuospatial memory could affect the ability to adapt offline body representation based on new information and form a correct visual representation of the body, respectively6,10,14. C O R R E S P O N D E N C E
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