A new look at working memory deficits in schizophrenia

Abstract

Working memory deficit has been suggested to be a cardinal feature of schizophrenia, but the causes of this deficit have not been determined. This dissertation intended to augment our understanding of the etiology of working memory deficit in schizophrenia using both behavioral and functional and structural brain imaging methods. The behavioral studies, focusing on elucidating the relationship between context processing and working memory, found that task-irrelevant contextual information facilitated working memory performance of schizophrenia whether the contextual information was embedded within the target or was provided by the spatial layout surrounding the target. These findings suggest that schizophrenia patients have an intact ability to process certain types of context and, therefore, it is necessary to examine context processing systematically instead of portraying ‘context processing’ deficit as the fundamental core feature of schizophrenia. Functional brain imaging studies using fMRI and near-infrared spectroscopy revealed markedly different brain activation patterns during spatial working memory in schizophrenic patients compared with normal controls. While normal controls showed a clear right hemisphere advantage for processing visuospatial information, schizophrenia patients activated bilateral cortical areas in the brain. Finally, white matter connectivity was examined using diffusion tensor imaging to relate functional brain imaging data to structure. While the results are inconclusive, frontoparietal connectivity may play an important role in schizophrenia. These results depict a dynamic picture of the neural correlates of working memory deficit in schizophrenia that is neither a simple result of hypofrontality nor hyperfrontality, but probably be an outcome of a combination of recruitment of wider cortical network, altered connectivity between cortical areas and altered cognitive strategies. The findings of this dissertation provide a new perspective towards understanding working memory deficit and context processing in schizophrenia.