Melbourne School of Psychological Sciences - Theses

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End date: 2019 × Start date: 2010 × Type: PhD thesis × Subject: anomalous experiences × Subject: psychosis × Subject: schizophrenia ×

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    Evaluation of a continuum model of psychotic symptoms: evidence from neuroanatomical, neuropsychological and clinical correlates
    Nelson, Margaret Tasma ( 2012)
    The fully dimensional model of psychosis posits that schizotypal personality traits in psychologically healthy people lie on a continuum with the psychotic symptoms experienced by people with a psychotic illness. Therefore, it was anticipated that psychotic and psychotic-like symptoms would show similar correlates for both individuals with a psychotic illness and psychologically healthy individuals. The validity of this notion was evaluated across three studies, which examined relationships between positive symptom traits and a range of neuroanatomical, neuropsychological and psychological variables. Case participants involved in the three studies had a diagnosis of schizophrenia or schizoaffective disorder, and control participants were psychologically healthy. In Study 1, comprehensive phenomenological information was acquired from cases (n = 20 and controls (n = 30) regarding the nature and frequency of positive symptom traits. Significant differences were identified between groups in terms of how they responded to and appraised their own positive psychotic and psychotic-like experiences. Four of these responses (immersion, external and impersonal attributions, and lack of social understanding) were also associated with the frequency and severity of positive psychotic and psychotic-like experiences across all participants’ lifetimes. Study 2 examined both between-group differences and within-group relationships in relation to neurocognitive functioning. Cases (n = 167) had significantly lower mean scores than controls (n = 222) on measures of Full Scale IQ, immediate memory, visual construction, language, attention, delayed memory and working memory. Participants’ scores on a measure of working memory were negatively associated with the frequency and severity of positive psychotic and psychotic-like experiences across their lifetimes. In Study 3, diffusion weighted MRI was used to assess whether groups differed according to structural brain connectivity, and whether connectivity was related to the frequency and severity of psychotic and psychotic-like experiences. One measure of white matter connectivity (fractional anisotropy) was significantly lower for cases (n = 93) as compared to controls (n = 80) across diffuse areas of the brain. For control participants, fractional anisotropy measurements in the corpus callosum and inferior frontal and temporal areas were negatively associated with the frequency and severity of positive psychotic and psychotic-like experiences across participants’ lifetimes. The findings of the three studies identified similar relationships for both cases and controls between positive symptom traits and a range of neuroanatomical, neuropsychological and psychological variables. These were taken to broadly support a fully dimensional model of schizotypy and psychosis.