Anomia as a marker of distinct semantic memory impairments in Alzheimer's disease and semantic dementia.

OBJECTIVE Many neurologically constrained models of semantic memory have been informed by two primary temporal lobe pathologies: Alzheimer's disease (AD) and Semantic Dementia (SD). However, controversy persists regarding the nature of the semantic impairment associated with these patient populations. Some argue that AD presents as a disconnection syndrome in which linguistic impairment reflects difficulties in lexical or perceptual means of semantic access. In contrast, there is a wider consensus that SD reflects loss of core knowledge that underlies word and object meaning. Object naming provides a window into the integrity of semantic knowledge in these two populations. METHOD We examined naming accuracy, errors and the correlation of naming ability with neuropsychological measures (semantic ability, executive functioning, and working memory) in a large sample of patients with AD (n = 36) and SD (n = 21). RESULTS Naming ability and naming errors differed between groups, as did neuropsychological predictors of naming ability. Despite a similar extent of baseline cognitive impairment, SD patients were more anomic than AD patients. CONCLUSIONS These results add to a growing body of literature supporting a dual impairment to semantic content and active semantic processing in AD, and confirm the fundamental deficit in semantic content in SD. We interpret these findings as supporting of a model of semantic memory premised upon dynamic interactivity between the process and content of conceptual knowledge.