The tangled threads: Unveiling the interplay between the sense of body ownership and the sense of agency in impacting the bodily-self representation in eating disorders

The feeling of owning a body (body ownership) and controlling its actions (sense of agency) contributes to the emergence of the bodily-self representation, whose alteration is at the root of the central psychopathology of Eating Disorders (EDs). Yet, studies addressing these aspects in EDs provided inconsistent results. Here, we simultaneously test body ownership and sense of agency in EDs compared to controls by exploiting different rubber hand illusion (RHI) paradigms (i.e., classic visuo-tactile, passive and active visuo-motor versions). In any RHI versions, no differences in the susceptibility to the illusion between EDs patients and controls emerged at the body ownership questionnaire, thus suggesting a normal multisensory integration mechanism. Crucially, correlation analysis revealed that a higher level of body dissatisfaction is associated with increased susceptibility to RHI, as measured by the body ownership questionnaire. Interestingly, patients with a bulimic variant of EDs reported agency toward the fake hand in the visuo-tactile RHI, revealing an abnormal sense of agency in absence of voluntary movement. Moreover, in the visuo-motor RHI, EDs patients exhibited a proprioceptive drift both in synchronous and asynchronous conditions. Hence, our results revealed a dissociation between explicit and implicit RHI measures, showing a more plastic bodily-self representation when the RHI enlists hand movements, leading to a stronger visual-capture of proprioception. This study contributes to understanding the intricate link between body ownership and agency, shedding light on the role of voluntary actions in driving the sense of self in EDs.