Clustering and switching during verbal fluency in Alzheimer's disease and frontotemporal dementia

The purpose of this investigation was to distinguish between Alzheimer's Disease (AD) and Frontotemporal Dementia (FTD) using measures of word generation. Total word production, word clustering and switching were measured in 23 AD, 46 FTD, and 22 healthy control participants. We hypothesized that clustering is most decreased in AD and in the semantic dementia subtype of FTD, while switching is most reduced in the non-aphasic and progressive non-fluent variants of FTD. Our results revealed that the AD group showed a greater relative deficit on the semantic fluency test than the FTD group. As predicted, the AD and semantic dementia participants had more difficulty with task-consistent semantic clustering than the other FTD groups and controls. Although switching ability was reduced in the progressive non-fluent subtype, the non-aphasic variant did not show reduced switching scores. Comparisons of semantic and phonemic word generation and task consistent semantic clustering usefully distinguish subtypes of dementia.