Few studies have sought to understand the neurobiological mechanisms responsible for disrupting cognitive networks, even in the absence of depressed mood and/or anhedonic features; nor have they sought to evaluate the effect of treatments such as psychotropic medication, cognitive behavioral therapy, or cognitive remediation on cognitive function. This underscores the need for psychometric tests specifically developed to evaluate cognitive performance among individuals with depression; the absence of a “gold standard” psychometric of cognitive function in MDD highlights a research priority in mood disorders. 14
In those with MDD, measures of general cognitive function tend to be below average compared with age-matched healthy controls. However, variability between those with depression is also often observed, suggesting the presence of other mediating factors (eg, years of education, comorbid medical conditions that impact cognition, and treatment regimens).4, 15, 16 Evidence also indicates that subjective reports of cognitive complaints do not necessarily correlate with objectively measured cognitive performance. 4 That is, an individual’s experience of cognitive decline from premorbid state often does not translate as clinically significant based on standard objective measures of cognitive function. 4 The opposite phenomenon has also been reported, wherein objective measures of cognition indicate clinically significant deficits, but patients report no noticeable change in subjective evaluations of their cognitive function. 4, 17
Overall, the biological functions contributing to cognitive impairment, including neuroinflammation and metabolic disturbances, as well as the possibility of cognitive impairment eventually progressing to dementia, point to an urgent need to refine our understanding of the underlying causes behind cognitive impairment in MDD. Psychiatry needs to move towards preventing these debilitating and chronic disorders via disease modification, as opposed to focusing almost exclusively on mitigating symptoms.19
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