Working memory deficits in depression.

Abstract

Depressed individuals frequently complain of poor memory and concentration. In fact, cognitive dysfunction may be an intrinsic symptom of this mood disorder. The goal of this dissertation was to formulate a framework that would account for the cognitive impairments reported by depressive patients. Specifically, the executive process of task-switching in the working memory (WM) of depressed patients was examined. Depression is associated with an increase in the production of the stress hormone cortisol, which has been hypothesized to affect prefrontal cortical functioning. Since WM is known to recruit this region, the relationship between the WM changes associated with depression and abnormalities in the stress hormone levels were studied. In Study 1, the performance of middle-aged treatment resistant depressed participants on the Operation Span, a WM task that involve task-switching, was contrasted with that of age, education, and gender matched controls. Results revealed that compared to baseline performance, depressives paid a higher cost in performing the WM task than controls and that this impairment was linked to a greater increase in cortisol production. In Study 2, young newly diagnosed depressives who had a less extensive history of depression were examined on the Operation Span, and again, cortisol measures were taken. Results showed that depressed participants paid a higher cost in performing the WM task, but the association with cortisol increase was not replicated. Thus, even at the onset of depression, there is a deficit in the executive processing components of WM. When the measures from the two studies were contrasted, it became apparent that in addition to the effect of chronicity of depression on cognitive functioning, factors such as age and gender must also be considered.