Long-term course of intellectual and cognitive functioning in schizophrenia and bipolar disorder

Abstract

Schizophrenia and bipolar disorder (BD) are considered severe mental disorders. Cognitive impairments are commonly present at illness onset in both disorders and are related to poorer functional outcomes. This has given rise to questions about the role of cognition in the nature and development of these disorders. Findings of neuroanatomical and neurophysiological changes and more severe deficits in chronic samples have engendered neurodegenerative models of the disorders. Though schizophrenia is now generally regarded as a neurodevelopmental condition, the question of neuroprogression in BD remains disputed. However, several factors could explain the observed severe cognitive deficits in chronic stages of the illnesses, including confounding clinical factors and sampling bias. For this reason, long-term follow-up studies of recently diagnosed individuals are needed. The overarching aim of this study was to investigate the long-term intellectual and cognitive course in first-episode schizophrenia and first-treatment BD. The results show stable cognitive deficits and are broadly inconsistent with neurodegeneration as a model of schizophrenia and BD. The studies were limited by high attrition leading to small sample sizes at follow-up, precluding complex statistical models and subgroup analyses. Future research should focus on subgroup-level trajectories, investigate mediating factors in the cognitive course, and explore the potential long-term benefits of early intervention on cognitive outcome.