Semantic relations and Alzheimer's disease: an early and disproportionate deficit in functional knowledge.

This experiment explored knowledge of four types of semantic relations (superordinate category, part, property, and function) in Alzheimer's disease (AD) subjects and age- and education-matched controls. Moderate AD subjects showed the greatest disruption on functional relations, intermediate disruption on part and property relations, and the least disruption on category relations; mild AD subjects showed a similar pattern but significant deficits only on functions. We suggest that the disproportionate deficit on functions reflects a greater cognitive complexity of functions than other semantic relations that renders them more vulnerable either to disrupted processing or to structural degradation of the network of associations among semantic concepts.