Abstract
Major Depressive Disorder (MDD) is the most common psychiatric disease, affecting millions of people worldwide. In addition to the well-defined depressive symptoms, patients suffering from MDD consistently complain about cognitive disturbances, significantly exacerbating the burden of this illness. Among cognitive symptoms, impairments in attention, working memory, learning and memory or executive functions are often reported. However, available data about the heterogeneity of MDD patients and magnitude of cognitive symptoms through the different phases of MDD remain difficult to summarize. Thus, the first part of this review briefly overviewed clinical studies, focusing on the cognitive dysfunctions depending on the MDD type. As animal models are essential translational tools for underpinning the mechanisms of cognitive deficits in MDD, the second part of this review synthetized preclinical studies observing cognitive deficits in different rodent models of anxiety/depression. For each cognitive domain, we determined whether deficits could be shared across models. Particularly, we established whether specific stress-related procedures or unspecific criteria (such as species, sex or age) could segregate common cognitive alteration across models. Finally, the role of adult hippocampal neurogenesis in rodents in cognitive dysfunctions during MDD state was also discussed.
Highlights
Cognitive dysfunction is a common feature of major depressive disorder (MDD), contributing to the serious decline in patients’ quality of life
Whether these cognitive deficits are specific to a clinical subtype of MDD in Humans or to a specific chronic stress procedure in animal models of the disease remains to be further determined
We provided an overview of clinical findings regarding the nature of cognitive dysfunctions in depressed patients from the first episode to recurrence according to the subtype of MDD
Summary
Cognitive dysfunction is a common feature of major depressive disorder (MDD), contributing to the serious decline in patients’ quality of life. Described in the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V, [1]) as “significantly affecting the individual’s capacity to function”, these cognitive changes are associated with the set of emotional and behavioral alterations (including persistent depressed mood and loss of pleasure) that characterizes MDD pathology. Patients mostly report their difficulty to concentrate, to make decisions, the feeling that their brain is slowed down or the fact that “they forget everything” (tasks, meetings, etc.) [7]. These subjective complaints relate to a broad range of cognitive impairments reported during depressive episodes, from executive functions (attention, processing speed, cognitive flexibility) to working and visual learning and memory. Contradictory findings from neuropsychological tests have encouraged clinicians to examine whether the heterogeneity of the MDD population would prevent from identifying a specific neurocognitive profile in depressed individuals
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