Strategies and structures in verbal fluency tasks in patients with Alzheimer's disease.

Reduced word production in verbal fluency tasks is a sensitive indicator for brain damage. Patients with Alzheimer's disease (AD) are supposedly more affected in semantic than in letter fluency, which is probably resulting from partially destroyed structure of semantic knowledge, whereas in letter fluency tasks the patients can use phonemic cues for searching. In this study, 21 patients with probable AD according to NINCDS-ADRDA criteria were examined on a verbal fluency task with F, A, S as initial letters, and a supermarket task. Performances were compared with a control group. Patients with AD showed lower word rate in all tasks than the control group. The difference was most significant in the supermarket task. Both groups produced most of the words in the supermarket task, followed by S, A and F. They both showed a percentuallikely distribution pattern of items into different supermarket categories. The items of the supermarket task were mostly ranged in clusters (patients with AD 70%, control group 83%). Patients with AD, however, on average, used fewer categories which they also filled with fewer items. In the F, A, S test, patients with AD mainly produced nouns, whereas the control group named nearly twice as many adjectives and verbs. In patients with AD word generation was highly correlated with degree of dementia, free recall of a verbal memory task, and the Token test. Low word production and qualitatively changed output in patients with AD might relate to an inefficient searching strategy, attentional deficits and/or degraded semantic knowledge.