Cognitive impairment in unipolar depression is persistent and non-specific: further evidence for the final common pathway disorder hypothesis

Background. Cognitive performance is often impaired in depression, and these impairments can persist even after remission from psychopathological symptoms. However, it is still unclear whether cognitive dysfunction is associated with psychopathological symptoms or represents a genuine disorder. This study examined cognitive performance in acute depression, after remission, and 6 months after remission in order to determine the nature and specificity of cognitive dysfunction as well as its relevance for the further course of depression. Method. Assessments of cognitive function and psychopathology were carried out on admission and prior to discharge in 53 in-patients with unipolar depression. Twenty patients were retested 6 months after discharge. To correct for practice effects, 13 healthy subjects were included and assessed twice with the same cognitive tests. Results. In acute depression, we found impairments of information processing/attention, memory, and executive functions. Cognitive impairments remained in a high proportion of patients, even after remission of psychopathological symptoms. After correcting for practice effects, a significant improvement was observed only for some tests of executive functioning. Severity of depression was only weakly correlated with one single cognitive measure, indicating that psychopathological and neuropsychological symptoms are dissociable. Furthermore, we found no evidence for specific cognitive dysfunction. Conclusions. Our results support the hypothesis that cognitive impairments in depression are neither selective nor specific; they have trait-like features and are, therefore, not merely an epiphenomenon of depression. Whether or not cognitive dysfunction is a prognostic marker for the course of depression remains still an open issue.