Body representation disturbances in anorexia nervosa

Abstract

One of the main symptoms of anorexia nervosa (AN) is a disturbed experience of body size and shape. Although patients are underweight, they experience their body as bigger than it in reality is. Previous studies were mainly conducted by (clinical) psychologists and psychiatrists, and almost exclusively focused on bodily cognitions and visual processing of body-related information. In this thesis a more cognitive neuroscience approach was adopted. This allowed for investigating multimodal body image disturbances, body schema disturbances, and the plasticity of body representation in AN. Body image is mainly involved in conscious body-related perception. We developed and validated a task which assesses the metric aspects of tactile body image. Participants were blindfolded and received two simultaneous tactile stimuli to their forearm and abdomen. The results showed that compared to healthy females, AN patients overestimated the distance between the two tactile stimuli. This implies a disturbance in tactile body image in AN. Group differences on tasks assessing lower level somatosensory perception were identified as well. Regression analyses indicated that overestimation of tactile distances in the AN group is related to higher order aspects of AN pathology as well as to lower level aspects of tactile perception (at receptor level). The (unconscious) body schema is crucial in planning and performing actions. We developed and validated a task that assesses body schema disturbances. Participants walked through apertures varying in width. Notably, participants were led to believe that the apertures were not of relevance, and that they participated in a haptic memory experiment. This ensured that participants did not consciously focus on their walking behaviour. The results showed that healthy females started rotating their shoulders as soon as an aperture was 25% wider than their own shoulders. AN patients, however, already started rotating their shoulder for apertures that were 40% wider than their own shoulders. AN patients thus rotated their body for apertures that they could objective walk straight through. This indicates that AN patients movements are based on an enlarged internal model of body size, i.e. they show a disturbance in body schema. Plasticity of body representation in AN was assessed with an adapted version of the Rubber Hand Illusion (RHI). Here participants estimated the size of their own hand and a rubber hand before and after induction of the RHI. In both the experimental and control condition participants estimated their own hand more accurately after multisensory input during induction of the RHI was provided (i.e. stroking of the own occluded hand and the visible rubber hand). This implies that the disturbed experience of body size in AN is not static but can be changed. Taken together the present thesis shows that the disturbed experience of body size goes beyond “merely” thinking and seeing the own body as fat, it even affects perception of touch and unconscious movements. AN patients feel fatter with their body and behave as if they are bigger than they actually are. It was also shown that the disturbed experience of body size can be corrected using multisensory input.