| Summary: | Cognitive impairments are present in both schizophrenia and bipolar disorder and are strong predictors of functional outcomes for patients. One barrier in cognitive research of these disorders is the lack of large, well-characterised cross-disorder samples with cognitive data. The aims of this thesis were to examine cognition across the bipolar / schizophrenia diagnostic spectrum and to develop a new online cognitive battery for use in psychiatric research. Cognition was examined in participants with bipolar disorder, schizoaffective disorder and schizophrenia through a meta-analysis of existing studies and analysing data from a large well-characterised sample. The main finding was that there is a gradient of increasing cognitive impairment from bipolar disorder through schizoaffective disorder – bipolar type to schizoaffective disorder – depressive type and schizophrenia. Participants with the subtypes of schizoaffective disorder differed in their cognitive performance. Lifetime history of psychosis was associated with cognitive performance across disorders. An online cognitive battery was developed to assess the domains outlined by the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative. The battery was validated against the MATRICS Consensus Cognitive Battery and showed that the tasks provided valid measurements of the majority of the MATRICS domains. A large sample of participants with a range of psychiatric disorders was recruited online. An examination of cognition in participants with major depressive disorder, bipolar disorder and schizophrenia showed that cognitive profiles were similar across disorders but participants with schizophrenia have more severe impairments than participants with bipolar disorder. An important concluding observation was that poorer cognitive performance was associated with poorer functional outcome across disorders. The findings of this thesis add to a growing literature showing the importance of examining cognitive function across psychiatric disorders. To date, it is the first study to develop and utilise an online cognitive assessment for psychiatric research.
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