Memory and processing speed impairments in first-episode drug-na?ve patients with major depressive disorder

Background: Cognitive impairment, an intrinsic feature of major depressive disorder (MDD), affects daily and social functioning in depression patients. However, the cognitive impairment profile in MDD remains ambiguous because of the high heterogeneity of previous studies.Methods: Four cognitive domains, including memory, processing speed, executive function (EF), and attention, were assessed in 184 first-episode drug-naive (FEDN) MDD patients and matched 71 healthy controls (HCs). The effects of demographic and depressive factors on cognitive performance were analyzed using various statistical methods, including multi-factor analysis of variance, Mann-Whitney U test, and Spearman's rank correlation. In addition, the impact of depression severity on cognitive function was further assessed using subgroup analyses and partial correlation analyses. Results: Age and education significantly impacted most cognitive performances, and depression severity appeared to influence processing speed. Moreover, cognitive scores in memory and processing speed, rather than in EF and attention, were significantly different between FEDN MDD patients and HCs after controlling for sex, age, educational attainment, household income, and body mass index. Limitations: The number of HCs was relatively small, which may have slightly reduced the study's statistical power.Conclusions: Age and educational attainment have confirmative confounding effects greater than those of depression in most cognitive functions. More importantly, memory and processing speed were impaired in MDD after strictly controlling for confounders. These findings provide new information for understanding the pattern of cognitive impairment and offer clues for further exploring the pathogenesis of cognitive abnormalities in MDD.