Cognitive function in first episode major depressive disorder: poor inhibition and semantic fluency performance

Executive Functions (EF) has been documented to be impaired in patients with recurrent Major Depressive Disorder (MDD) in several studies. Longitudinal studies have suggested that these impairments may be a result of several episodes of depression or they may represent stable traits in this patient group. However, few studies have addressed these issues and investigated cognitive functioning with a particular focus on EF in patients who experience MDD for the first time.

In the present study, the executive functions of inhibition, verbal fluency, mental flexibility, and planning and problem solving were investigated in a group of patients diagnosed with first episode MDD. Thirty patients and 30 control subjects were included in the study.

The patient group performed significantly more poorly in the cognitive functions of inhibition and semantic fluency. In addition, the patient group showed a reduced speed of mental processing on some of the measures. However, the results showed that reduced processing speed alone could not account for the poor performance in inhibition and semantic fluency. There were no differences between the two groups in the other measures of EF, indicating that functioning of mental flexibility, phonemic fluency, planning, and problem solving was intact in the patient group.

The results show that impaired inhibition and semantic fluency are present early in the course of MDD. The present findings indicate that poor inhibition and performance in semantic fluency may represent stable traits in MDD, independent of symptom severity and the number of depressive episodes.