Longitudinal course of cognitive function across treatment in patients with MDD: A meta-analysis.

BACKGROUND: The longitudinal change of cognitive function across psychological treatment remains unclear. The aim of this meta-analysis was to synthesize results from longitudinal studies of cognitive deficits in MDD patients across treatment to examine change and determine domains that are most sensitive to change.

METHODS: A literature search was conducted using PsycINFO, MEDLINE, Science direct, and Google scholar databases. The main analysis included 16 studies and examined the change of cognitive function in 859 patients with MDD by calculating overall test-retest effect sizes (Hedges' g) and using a random effects model. Further analyses were conducted on studies of MDD patients that included a healthy control group, and effect sizes were compared.

RESULTS: The effect size estimates suggest significant small improvements in all cognitive measures (g = 0.17-0.35). Studies including healthy controls revealed no significant differences in cognitive function between MDD patients and healthy controls, except for the improvements in verbal memory. Moderator analyses revealed that mean age influenced change in some cognitive domains. The change in depression severity did not affect the results.

LIMITATIONS: Treatments differed with regard to the type and duration of psychological intervention and the influence of additional pharmacological treatment could not be controlled. Due to the small number of included studies, the results should be regarded as preliminary.

CONCLUSIONS: Cognitive abilities improved during treatments, which included psychological interventions. The improvements may be due to practice effects rather than cognitive recovery, except for verbal memory.