Cognitive function in late life depression: Relationships to depression severity, cerebrovascular risk factors and processing speed

Background- A number of studies have examined clinical factors linked to worse neuropsychological perfori-nance in late life depression (LLD). To understand the influence of LLD on cognition, it is important to determine if deficits in a number of cognitive domains are relatively independent, or mediated by depression-related deficits in a basic domain such as processing speed. Methods. Patients who met DSM-IV criteria for major depression (n = 155) were administered a comprehensive neuropsycbological battery of tasks grouped into episodic memory, language, working memory, executive function, and processing speed domains. Multiple regression analyses were conducted to determine contributions ofpredictor variables to cognitive domains. Results. Age, depression severity, education, race and vascular riskjactors all made significant and independent contributions to one or more domains of cognitive function, with allfive making independent contributions to processing speed. Age of onset made no independent contribution, qfter accountingfor age and vascular risk factors. Of the five cognitive domains investigated, changes in processing speed werefound to most,fully mediate the influence ofpredictor variables on all other cognitive domains. Conclusions: Wbile slowed processing speed appears to be the most core cognitive deficit in LLD, it was closely followed by executive function as a core cognitive deficit. Future research is needed to help clarify mechanisms leading to LLD-related changes in processing speed, including the potential role of white matter abnormalities.