Depression Leads to Cognitive Impairments.

Cognitive impairments may be the result of an underlying primary psychiatric disorder, as cognitive problems are a key symptom of (late-life) affective disorders. In this case, the affective diseases might cause cognitive complaints without any involvement of neurodegenerative pathologies. A quantitative review found that depressed patients indeed had impairments in several cognitive domains [22]. Cognitive deficits in depressed people are often explained by effort-related problems. However, other evidence proposed that reduced attention mechanisms might have a role in explaining other (secondary) cognitive dysfunctions in depression [22].

Differentiation between cognitive problems due to depressive disorders and MCI due to AD is complex as affected cognitive domains in both conditions are widespread and therefore largely overlap. In clinical MCI patients, also memory and executive impairments can already be objectified many years before the syndromal diagnosis of dementia can be made [30]. Therefore differentiation based on crosssectional cognitive test performances or cognitive profiles in an early phase may be problematic.

Depressive symptoms also increase the risk of developing incident cognitive impairments and decline over time [31]. In this study, however, the involvement of underlying neurodegenerative pathologies was not investigated and could therefore not completely be excluded. Recent findings from the prospective Leukoaraiosis and .Disability in the Elderly Study (LADIS) also showed that depressive symptoms in older people were predictive for cognitive decline over time and that this effect was independent of degenerative processes, such as medial temporal lobe atrophy or white matter changes [32].

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