Painfully Thin but Locked Inside a Fatter Body: Abnormalities in Both Anticipation and Execution of Action in Anorexia Nervosa

Background: People 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.

Methods: Fourteen 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.

Results: We 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.

Conclusion: The 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.