BackgroundPeople with anorexia nervosa (AN) usually report feeling broader than they really are. The objective of the present study was to better understand the body schema's involvement in this false self-representation in AN. We tested the potential for correction of the body schema impairment via the sensorimotor feedback provided by a real, executed action and relative to an imagined action. We also took account of the impact of the AN patients’ weight variations on the task outcomes.MethodsFourteen inpatient participants with AN and fourteen control participants were presented with a doorway-like aperture. The participants had to (i) judge whether or not various apertures were wide enough for them to pass through in a motor imagery task and then (ii) actually perform the action by passing through various apertures.ResultsWe observed a higher passability ratio (i.e. the ratio between the critical aperture size and shoulder width) in participants with AN (relative to controls) for both motor imagery and real action. Moreover, the magnitude of the passability ratio was positively correlated with weight recovery.ConclusionThe body schema alteration in AN appears to be strong enough to affect the patient's actions. Furthermore, the alteration resists correction by the sensorimotor feedback generated during action. This bias is linked to weight variations. The central nervous system might be locked to a false representation of the body that cannot be updated. Moreover, these results prompt us to suggest that emotional burden during weight recovery could also alter sensorimotor aspects of body representation. New therapeutic methods should take account of body schema alterations in AN as adjuncts to psychotherapy.

Behavioural therapy and bariatric surgery often produce rapid, massive body weight loss that may impact a patient's ability to gauge his/her new body shape. Although the patient is aware of the weight loss, he/she continues to feel obese, as if there was a conflict between the previous body schema and the new one. Here, we report the case of a 40-year-old woman who developed major body distortions after massive weight loss. Psychometric and behavioural assessments revealed strong disturbances in several tasks involving body representation. In particular, we observed abnormal behaviour in a body-scaled action task. Our findings suggest that the rapidity of our patient's weight loss prevented her central nervous system from correctly updating the body schema.

Position sense and kinaesthesia are mainly derived from the integration of somaesthetic and visual afferents to form a single, coherent percept. However, visual information related to the body can play a dominant role in these perceptual processes in some circumstances, and notably in the mirror paradigm. The objective of the present study was to determine whether or not the kinaesthetic illusions experienced in the mirror paradigm obey one of the key rules of multisensory integration: spatial congruence. In the experiment, the participant's left arm (the image of which was reflected in a mirror) was either passively flexed/extended with a motorized manipulandum (to induce a kinaesthetic illusion in the right arm) or remained static. The right (unseen) arm remained static but was positioned parallel to the left arm's starting position or placed in extension (from 15° to 90°, in steps of 15°), relative to the left arm's flexed starting position. The results revealed that the frequency of the illusion decreased only slightly as the incongruence prior to movement onset between the reflected left arm and the hidden right arm grew and remained quite high even in the most incongruent settings. However, the greater the incongruence between the visually and somaesthetically specified positions of the right forearm (from 15° to 90°), the later the onset and the lower the perceived speed of the kinaesthetic illusion. Although vision dominates perception in a context of visuoproprioceptive conflict (as in the mirror paradigm), our results show that the relative weightings allocated to proprioceptive and visual signals vary according to the degree of spatial incongruence prior to movement onset.