The nature of the memory deficit in geriatric depression

Abstract

Cognitive dysfunctions are an integral feature of geriatric depression. Evaluating the source of a memory impairment in a depressed elderly patient requires distinguishing between memory deficits due to depression and memory deficits due to normal aging. This process is complicated by the fact that both depression and normal aging are associated with impaired attention, use of inefficient processing strategies, and reduced processing capacity. Assessment can be further complicated by use of antidepressant medications, some of which have anticholinergic properties, and by the possibility that a depressed patient is also in the early stages of dementia. The purpose of this study was to determine whether a memory test which controlled for attentional factors and inefficient semantic processing would benefit a group of 25 non-demented geriatric patients with major depression to the point that they would perform just as well as a group of 25 non-demented normal controls. Findings revealed that depressed patients recalled significantly fewer words than controls. Although manipulations designed to improve semantic processing and attention were found to have a beneficial effect on free recall for both the controls and the depressed subjects, the depressed subjects still performed significantly worse. Controlling for age, Verbal IQ, Mini-Mental State score, and depression severity did not significantly change the pattern of results. When cued recall scores were added to the free recall scores to provide a measure of total recall, 16 subjects (14 depressed and 2 normal controls) were found to score below a cut-off which in previous work has been shown to be indicative of dementia. These depressed subjects also had a later onset of depression which in other studies has been shown to be related to dementia. Lastly, the depressed subjects who performed below this cut score were less likely to be taking antidepressant medication. In sum, this study raises the possibility that at least some of the conflicting findings in the literature on the nature of the memory deficit in geriatric depression may be due to the inclusion of a group of depressed elderly in the pre-clinical stages of dementia. Findings also suggest that antidepressant medication can mediate memory performance and must be taken into account when conducting memory studies with a depressed population.