Cognitive hierarchy in mood disorders and relations to daily functioning.

Cognitive impairment affects approximately 50 % of patients with mood disorders during remission, which correlates with poorer daily-life functioning. The hierarchical organisation of cognitive processes may mean that some cognitive deficits, e.g., memory impairments, are secondary to impairments in suggested core processes, including executive functions, working memory, attention, and psychomotor speed. The exact structure of a cognitive hierarchy in mood disorders is unclear. In this study, we aimed to examine relationships between cognitive domains using network graphs. Further, we aimed to explore whether impairments in the proposed 'core cognitive domains' mediated patients' verbal memory impairment and functional disability using mediation and hierarchical regression analyses. We pooled data from patients with mood disorders and healthy controls (HC) from 10 original studies. In total, 1505 participants were included in the analyses (n = 900 patients; n = 605 HC). We found that cognitive domains were more intercorrelated in patients than in HC. Executive functions, working memory, and attention and psychomotor speed almost fully accounted for illness-associated verbal learning and memory impairments, indicating partial mediation. Of the core domains, working memory explained the largest amount of variance in memory impairments and functional disability. Our findings highlight the importance of targeting core cognitive domains in pro-cognitive interventions.