12. IMPAIRED PERCEPTION OF ONE’S OWN BODY IN SCHIZOPHRENIA: NEW EXPERIMENTAL EVIDENCE

Abstract

Self-disturbances in schizophrenia include symptoms such as depersonalization, fuzzy demarcation between one's own body and others, feelings of body disintegration or dislocation, the feeling of a distance between oneself and the world, and experiences of time fragmentation or disappearance. These are only a few examples of symptoms related to bodily or 'minimal' self-disturbances, which have been described both in patients with prodromal symptoms and chronic schizophrenia. Contrary to agency disorders, the listed symptoms do not imply voluntary actions, and may occur even when one stands still. They are non-verbal manifestations by definition, and thus hard to describe for the patients. Recent phenomenological developments have nonetheless brought these symptoms back to the forefront. However, compared to the exploration of agency disorders, experimental evidence for disorders of body self-perception is still scarce. The aim of the symposium is to bring together the work of four teams that have independently explored this question with distinct experimental psychology approaches. The sense of bodily self and the ability to see the world from one's own first-person perspective relies on the integration of both interoceptive and exteroceptive information. Being 'immersed in the world', the impression of being in direct contact with the environment, relies on the ability to correctly attribute and integrate information from the outer world relative to oneself, and to synchronize oneself with the environment. It is precisely these abilities that are explored by studying the processing of interoceptive and multisensory information or time prediction, and the sensitivity to asynchronies. Lénie Torregrossa explores interoceptive signals in patients with schizophrenia by looking at their ability to accurately report heartbeats, and to precisely localize emotions in their body. Both abilities are affected in patients, and the results represent a unique insight in the alteration of how patients feel their own body. Anne Giersch explores time disorders and shows behavioral and EEG results suggesting that instead of reaching a sense of time continuity, patients with schizophrenia are abnormally sensitive to short asynchronies. She argues that such difficulties may affect the flow of sensory signals, and thus the bodily self. Neeltje van Haren explores body self-perception disorders using the rubber hand illusion, which is based on visuo-tactile stimulation. Patients report that the rubber hand feels like their own hand more than controls, reflecting the fragility of the patients' body boundaries. Interestingly, agency disorders are explored in parallel, and the results allow for discussion of the relative roles of sensorimotor input vs. the cognitive body representation in sensitivity to the illusion. Roy Salomon induces a feeling of presence experimentally, and shows it affects the ability of first episode patients to distinguish between their own voice and the voice of another person. This deficit correlates with resting-state fMRI dysconnectivity in the cortical systems of bodily self-representations. Voice misattributions have been shown in people with auditory hallucinations, these results thus relate body ownership impairments with agency disorders. The presentations, taking different perspectives, provide complementary descriptions of body self-perception disorders and of their underlying mechanisms. The discussant (Steve Silverstein) will integrate these data on body self-perception disorders in schizophrenia and discuss potential mechanistic interpretations and therapeutic implications.