Changes in semantic memory in early stage Alzheimer's disease patients.

The types and number of exemplars of categories that are retrieved from semantic memory differentiate elderly normal controls and early stage Alzheimer's disease (AD) patients. Elderly normal controls generated more uncommon exemplars from closed semantic categories (fruits and vegetables) than did AD patients 2 1/2 years prior to the presumed onset of AD. AD patients, however, were just as productive as elderly normal controls in generating associations to open categories (letters). The findings suggest that one of the early cognitive symptoms of AD is changes in availability of uncommon exemplars of semantic networks.