Cognitive functioning in severe psychiatric disorders: a general population study

In clinical samples, patients with severe psychiatric disorders are found to have cognitive impairments. Less is known whether this applies to samples derived from the general population. We aimed to study cognitive functioning in a population-based sample comprising individuals with schizophrenia, other non-affective psychoses, bipolar disorders, major depressive disorder, and controls derived from the same population. The current analysis was based on 148 persons with severe mental disorders and 66 control subjects, derived from the Psychoses in Finland study. All subjects were interviewed with SCID, and a neuropsychological test battery was administered. Subjects with schizophrenia had a generalized cognitive impairment (d = 0.43-1.07), while those with other non-affective psychoses were impaired in verbal memory and processing speed (d = 0.43-0.59). Subjects with bipolar disorders were not impaired. Unipolar major depressive disorder associated with slowed processing speed (d = 0.64). Our findings on cognitive impairments in subjects with schizophrenia and other non-affective psychoses derived from the general population support previous findings of a generalized cognitive dysfunction in these subjects. However, our results suggest that subjects with bipolar disorders from non-clinical populations may not have significant cognitive impairments. Our results emphasize the importance of using control samples derived from the same population and studied similarly as those with disorders in evaluating cognitive functioning of subjects with severe mental disorders.