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Neurocognition and language in the causes and consequences of formal thought disorder in schizophrenia
thesisposted on 2017-02-21, 05:09 authored by Tan, Eric
Unusual patterns of speech and word use are considered a hallmark feature of schizophrenia. Considerable debate has raged as to the exact nature of these phenomena, traditionally referred to as formal thought disorder (TD). A substantial body of empirical work supports both neurocognitive and language explanations in the aetiology of TD, but a comprehensive understanding of TD aetiology and functional impact is still lacking. This thesis sought to address a number of gaps in the neurocognitive and language literature of schizophrenia and TD. In addition to investigating TD mechanisms, the consequences of TD symptoms on quality of life (QoL) in schizophrenia were also examined to expand the currently minimal evidence base. This two-pronged approach had two aims. The first was a joint examination of neurocognitive and language function and their relationship to TD and each other in schizophrenia. To this end, the general neurocognitive profile of schizophrenia TD was examined (Chapter 3). This was followed by an examination of semantic processing theories in TD (Chapter 4). The pattern of language comprehension abilities in the sample was also assessed (Chapter 5); and the existence of a language-specific impairment in schizophrenia, in relation to TD and independent of neurocognition, was tested (Chapter 6). The second aim was to assess if the communication difficulties of TD independently impact on daily functioning and how patients perceive their QoL. For this, the predictive value of TD severity on QoL was assessed while factoring in the previously established effects of depression, neurocognition and general positive and negative symptomatology (Chapter 8). A group of schizophrenia/schizoaffective disorder patients and a group of healthy controls were assessed concurrently on a number of neurocognitive and language tasks; and measures of life functioning and satisfaction. The results indicated specific neurocognitive impairments of semantic and executive functioning in TD which confirm previous empirical findings. A further examination of semantic dysfunction revealed an underlying role for disorganised semantic memory storage in schizophrenia that is related to TD symptoms even in the non-florid TD phase. Abnormalities in single word and sentence comprehension in schizophrenia are reported, which do not appear to be related to lexical memory dysfunction. Phonological similarity appears to be a distracter for single word meaning attribution in TD; however specific language impairment is evident only for syntactic comprehension, which appears to be further exacerbated in TD. TD also appears to differentially affect daily functioning and life satisfaction. Verbal underproductivity leads to reduced social contact and activities, while aspects of regulation that drive positive TD elements, like pressured speech, lead to higher life satisfaction ratings. These findings support the notion that specific neurocognitive impairments (semantic and executive dysfunction) contribute to TD presentation, and that severity of TD may be dependent on severity of neurocognitive dysfunction. They also suggest a selective language level impairment in TD, which independently contributes to symptomatology alongside neurocognitive deficits. The findings are discussed in relation to methodological and research-related issues, as well as treatment implications.