The deterioration of semantic memory in Alzheimer's disease

Semantic memory impairment is a common feature of dementia of the Alzheimer type (DAT). Recent research has shown that patients with DAT are more impa ired (relative to non-demented controls) in generating exemplars from a par ticular semantic category (e.g., animals) than words beginning with a parti cular letter, exhibit an altered temporal dynamic during the production of category exemplars, are impaired on confrontation naming tasks and make pre dominantly superordinate or semantically related errors, consistently misid entify the same objects across a variety of semantic tasks, and have altera tions in multidimensional scaling models of their semantic network that are indicative of a loss of concepts and associations. These results are consi stent with the view that Alzheimer's disease results in a breakdown in the organization and structure of semantic knowledge as neurodegeneration sprea ds to the association cortices that presumably store semantic representatio ns.