Working memory demands and semantic sensitivity for prose in mild Alzheimer's disease

The debate continues with regard to whether degradation of semantic knowledge or deficits in information processing lead to impaired memory performance in patients with Alzheimer's disease (AD). This study examined the effects of semantic content and working memory demands on the recall and recognition abilities of patients with mild AD. Nineteen patients with probable AD and 19 demographically matched normal control participants were asked to remember prose passages that varied in semantic content thigh, medium, and low level of idea importance) and working memory demands (narrative and expository passages). Compared to the controls, patients with mild AD lost the ability to recall prose in a manner consistent with the semantic structure of the passages as the demands on working memory increased. Furthermore, as the demands on working memory increased, patients recognized information in a manner that suggested their initial processing was of isolated details rather than by semantic structure. This study provides support for the hypothesis that information processing deficits contribute to impaired semantic processing in patients with mild AD.