Cognitive Function's Importance to Recovery in Depression
Patients commonly report inter-episodic cognitive complaints during the “remitted” phases of depression that negatively affect their ability to engage in more cognitively demanding activities.
Major depressive disorder (MDD) has the highest lifetime prevalence of any psychiatric disorder. Rates of chronic MDD are conservatively estimated to be at approximately 20%, with high rates of relapse and recurrence also reported.1
It has been hypothesized that deficits in cognitive processes are predictive of future major depressive episodes. Available evidence suggests that over 25% of the impact of a major depressive episode on role functioning and psychosocial outcomes is mediated by cognitive function.2, 3 Patients also commonly report inter-episodic cognitive complaints during the “remitted” phases of the disorder that negatively affect their ability to engage in more cognitively demanding activities. This may contribute to limitations in their cognitive capacity even in the absence of depressed mood.4
While there is accumulating evidence that cognitive impairments are clinically significant, replicable, and consistent among individuals with MDD, few studies have primarily aimed to evaluate the impact of impaired cognition on overall psychosocial functioning in this clinical population.5-7
New literature on cognition in MDD has suggested that cognitive function can be separated into 2 broadly interrelated categories: 1) cognitive processing of non-emotionally valenced stimuli (eg, problem solving and planning) and 2) the perception, recognition, and modulation of emotionally valenced stimuli.8, 9
Models of the dynamic and reciprocal nature of cognitive-affective interactions suggest that individuals with MDD display heightened “bottom-up” response (eg, neurobiological processes) to emotional stimuli and diminished “top-down” cognitive control.10, 11 Cognitive resources are limited in their capacity (eg, working memory) and require relevant information to be updated efficiently in order to remain aware of internal and external changes. However, if the selection, sequencing, and monitoring of internal and external incoming information are disrupted by negative information, that interrupts the cognitive strategies generated to achieve a specific goal, and the “bottom-up” response has commandeered the individual's ability to remain focused.12, 13 This hypothesis is supported by reports estimating that approximately 20% to 30% of individuals with MDD exhibit pronounced cognitive impairments in executive function (eg, working memory and attention), representing a phenotypic manifestation of alterations in brain structure, function, chemical composition, and circuitry within and across distributed brain networks.5, 8, 9