Alterations of body representations associated with passivity symptoms in schizophrenia

Kyran Trent Graham-Schmidt

    Research output: ThesisDoctoral Thesis

    226 Downloads (Pure)

    Abstract

    [Truncated] People with schizophrenia and passivity symptoms feel they are not in control oftheir actions, intentions, thoughts and other somatic experiences, believing them to becontrolled by an external agent. A recent hypothesis posits that these symptoms arisefrom compromised mental and neurological representations of the physical body (‘bodyrepresentations’). Evidence exists of body representation alterations in schizophrenia,but have been incompletely characterised in this clinical group, and the specificity ofsuch disturbances to passivity symptoms is unclear.

    The overall hypothesis of this thesis is that there is a continuum of alterations ofbody representations (body schema, body image, body structural description, bodyagency) in all individuals with schizophrenia relative to healthy controls, such thatindividuals with a past history of passivity symptoms have more pronouncedabnormalities of body representations and the most prominent alterations are in peoplecurrently experiencing passivity symptoms.

    Two samples were used; healthy community controls were used to validateexisting tools to assess body representations (projected hand illusion in Chapter 2, andintentional binding task in Chapter 5), and determine the association with selecteddemographic variables and psychosis-like experiences (PLE). A sample of individualswith schizophrenia with and without passivity symptoms was also tested to assess theirperformance on tasks assessing body representations (Chapters 3, 4, 6).

    In chapter 2, a questionnaire assessing body image and body agency in theprojected hand illusion (PHI) was validated in 48 healthy controls. Principlecomponents analysis revealed four components: Embodiment and Disembodiment(body image), Agency (body agency), and Deafference. Increased embodiment of theproject hand was positively correlated with PLE scores, and negatively with age.

    In chapter 3, body schema (using a hand laterality task; HLT) and body imageand body agency (using the PHI) were investigated in people with schizophrenia(Current passivity symptoms = 20; Past history of passivity symptoms, n = 12; andNever experienced these symptoms, n = 21) and healthy controls (n = 48). Abnormalperformance on the HLT and PHI, indicated distortions of body schema and bodyimage, respectively, in all individuals with schizophrenia. People with any history (Past& Current) of passivity symptoms showed increased disembodiment and impairedprediction of the body schema and, in the Current group, insensitivity to the 500 msvisuotactile delay in the asynchronous condition.

    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2015

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