Patterns of neurocognitive impairment in first-episode bipolar disorder and schizophrenia

Background Researching psychotic disorders in unison rather than as separate diagnostic groups is widely advocated, but the viability of such an approach requires careful consideration from a neurocognitive perspective. Aims To describe cognition in people with bipolar disorder and schizophrenia and to examine how known causes of variability in individual's performance contribute to any observed diagnostic differences. Method Neurocognitive functioning in people with bipolar disorder (n=32), schizophrenia (n=46) and healthy controls (n=67) was compared using analysis of covariance on data from the Northern Ireland First Episode Psychosis Study. Results The bipolar disorder and schizophrenia groups were most impaired on tests of memory, executive functioning and language. The bipolar group performed significantly better on tests of response inhibition, verbal fluency and callosal functioning. Between-group differences could be explained by the greater proclivity of individuals with schizophrenia to experience global cognitive impairment and negative symptoms. Conclusions Particular impairments are common to people with psychosis and may prove useful as endophenotypic markers. Considering the degree of individuals' global cognitive impairment is critical when attempting to understand patterns of selective impairment both within and between these diagnostic groups.