A recent meta-analysis published in the Journal of Affective Disorders found that persons with major depressive disorder (MDD) see only a small improvement in their cognitive abilities during depression treatment. The study also found that the changes in cognitive abilities are independent of the change in depression severity, which could be due to practice effects rather than cognitive recovery, except for verbal memory.
For this study, the researchers performed a literature search using PsycINFO, MEDLINE, Science Direct, and Google Scholar databases between 1980 and December 2017. The study inclusion criteria were diagnosis of MDD in an adult sample, longitudinal assessment of cognitive functioning, first testing at the beginning of treatment, psychological outpatient or inpatient treatment intended to reduce depression, 4 weeks between test and retest, no specific cognitive training to improve cognitive functioning, and studies published in English or German. Studies were excluded if they included patients with mixed diagnostic groups or persons in a remitted state or with depression secondary to a somatic or organic brain disorder.
The principal analysis included 16 studies and examined the change of cognitive function in 859 patients with MDD by calculating the overall test-retest effect sizes (Hedges’ g) and using a random effects model. As a control group, the researchers also conducted a meta-analysis based on studies including a healthy control group both at test and retest. The overall test-retest effect sizes for patients with MDD and controls were calculated and compared.
In the MDD group, researchers found significant improvement in
- verbal memory,
- nonverbal memory,
- verbal fluency, and
- global cognition.
In the healthy controls, no significant intragroup effect sizes were found except for nonverbal memory, which suggests a practice effect on nonverbal memory. Studies including healthy controls revealed no significant differences in cognitive function between patients with MDD and healthy controls, except for the improvements in verbal memory. For verbal memory, participants with MDD improved significantly more than the persons in the healthy control group.
The effect size estimates suggest significant small improvements in all the cognitive measures (g=0.17-0.35). The moderator analyses revealed that the mean age influenced change in some cognitive domains. The change in depression severity did not affect the results.
Among the study limitations, the researchers recognize factors that could not be controlled, such as treatment differences in type and duration of the psychological intervention and the influence of pharmacological treatment. Moreover, the small size of the studies included makes the meta-analysis findings preliminary.
Considering the high rates of recurrence in patients with MDD and that the cognitive deficits may increase the risk for relapse, these findings suggest that common treatment approaches for depression do very little in improving cognitive function. Several researchers recommended a new goal for depression therapy focusing on cognitive remission as an alternative.
Bernhardt M, Klauke S, Schröder A. Longitudinal course of cognitive function across treatment in patients with MDD: A meta-analysis [published online February 6, 2019]. J Affect Disord. doi: 10.1016/j.jad.2019.02.021