Several lines of evidence suggest that in Alzheimer's disease (AD) there is a progressive degradation of the hierarchical organization of semantic memory. to evaluate this hypothesis, clustering and switching on phonemic and semantic fluency tasks were studied. For elderly controls, both clustering and switching were correlated with the numbers of correct words generated on both fluency tests, but the contribution of clustering was greater on the semantic task. Patients with AD generated fewer correct words and made fewer switches than controls on both fluency tests. the average size of their semantic clusters was smaller and the contribution of clustering to word generation was less than for controls. Severity of dementia was correlated with the numbers of correct words and switches, but not with cluster size. These results are consistent with various hypotheses which maintain that the structure of semantic memory in AD is degraded but provide no evidence that this process is progressive. Instead, progressive worsening of verbal fluency in AD seems to be more strongly associated with the deterioration of mechanisms that govern initiation of search for appropriate subcategories.

Patients with dementia who remain skilled at musical performance or playing bridge fail explicit memory tests for information related to their skills, suggesting that implicit memory mediates their preserved skills. To reexamine this issue, 23 dementia patients and 15 elderly controls of comparable domino-playing skill were compared on tests of naming, verbal fluency, and domino knowledge. On an explicit test of domino knowledge, the patients scored well below the elderly controls, performing no better than students who were unfamiliar with the game. But when game-like situations were created with real dominoes, both the skilled controls and the patients with dementia chose optimal moves and verbally explained their choices equally well. On naming and fluency tests, the skilled patients showed no advantage over patients of comparable dementia severity who had no retained skill. In dementia, some complex knowledge seems intact but is accessible only in particular contexts.

Preserved musical performance by patients with Alzheimer's disease (AD) has been attributed to an intact system for implicit musical cognition which may be localized in the right hemisphere. To examine this idea more thoroughly, we studied patient ML, a woman with AD who learned to play the piano as a child. Over three yearly evaluations, ML exhibited progressive deterioration in the following domains: language, visuospatial functions, attention, sequencing, picture priming, recognition of familiar songs, and discrimination of rhythm, meter, transposition, and major from minor keys, but pursuit rotor learning remained intact. By the third year of testing, ML also exhibited severe limb apraxia, but showed only subtle losses in the quality of her piano playing of familiar songs. She also showed immediate and accurate transfer of her playing skill from the piano to the xylophone. Preserved musical performance in AD seems to depend on circuits involving the basal ganglia, cerebellum and motor areas of the thalamus and cerebral cortex that remain relatively intact until the late stages of the disemse, but there is no evidence that the right hemisphere plays a special role in this phenomenon.

Normal elderly control participants showed short-term (10-min delay) and long-term (12 months delay) priming on the Gollin Figures Test. Nearly all patients with Alzheimer's disease or vascular dementia showed short-term priming, but the magnitude of their priming was less than that of controls. Significant long-term priming was not observed for the dementia groups. Differences between controls and dementia patients on the short-term priming test may depend upon structural–perceptual processes that are intact in dementia patients and controls and explicit memory functions available only to controls. The same model could account for differences between normal elderly and dementia patients on the long-term priming test, but several other explanations are also plausible. (JINS, 1998, 4, 336–341.)

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