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How the Body Can Feel Wrong : : Sensory Processing and Neural Body Representation in Transsexuality and Anorexia Nervosa

Abstract

While most people take identification with their bodies for granted, conditions like phantom limb pain, alien hand syndrome, and Xenomelia demonstrate that feelings of bodily congruence or incongruence are tied to neural construction of body image. Individuals with Xenomelia, for example, show reduced right parietal representation of body parts they find over-present and aversive. Similarly, transsexual individuals often find their untreated sexed body parts incongruent and aversive. Could differences in representation of these body parts in the right parietal lobe underlie this sense of bodily incongruity? Moreover, could a similar mechanism be involved in the counterfactual feelings of fatness in patients with anorexia nervosa (AN)? In this dissertation I investigate sensory processing and neural body representation of congruent and incongruent-feeling body parts in presurgical female-to-male (FTM) transsexual individuals, and dysphoric and neutral-feeling body parts in people with AN. Experiment 1 demonstrates heightened skin conductance response to tapping of the breast in presurgical FTM individuals, suggesting that aversion to body parts that feel incongruent extends to the level of automatic sensory processing. Utilizing magnetoencephalography (MEG), Experiment 2 demonstrates different integration of sensation from a body part that feels incongruent with one's gender. Experiment 3 reports diminished visual-tactile integration in individuals with AN, suggesting either greater reliance on somatosensory information or deficits in multisensory integration. Experiment 4 discusses differences in the somatosensory response (measured through MEG) to sensation from the abdomen between individuals with and without AN. Experiment 5 reports preliminary research on the use of allocentric mirror viewing strategies to correct body image distortion. I also report within-subject effects of body satisfaction on visual and tactile estimates of body size, suggesting rapid top-down modulation of sensory body representation. In summary, these studies demonstrate the presence of low-level differences in somatosensory processing for body parts that feel incongruent or dysphoric, suggesting strong connections between lower- level sensory representations of the body and higher-level, explicit body image and body dysphoria. This work advances our understanding of the involvement of sensory processing and sensory integration in the construction of experiences of body and self

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