Sentence comprehension in Alzheimer's disease.

We asked 22 patients with Alzheimer's disease (AD) to respond to simple probes of sentences where we manipulated grammatical factors, semantic factors, and cognitive resource demands associated with a sentence. The results demonstrated limitations in the cognitive resources needed to appreciate atypical syntactic-thematic mapping relations and difficulty processing selection restrictions associated with a verb. By comparison, comprehension in AD was not influenced by the active or passive voice of a sentence. These findings are consistent with the hypothesis that impaired sentence comprehension in AD is multifactorial in nature, including difficulty processing cognitive resource and semantic aspects of sentences.

Semantic memory in Alzheimer's disease: representativeness, ontologic category, and material.

Alzheimer's disease (AD) patients with semantic memory difficulty and AD patients with relatively preserved semantic memory named pictures and judged the category membership of words and pictures of natural kinds and manufactured artifacts that varied in their representativeness. Only semantically impaired patients were insensitive to representativeness in their category judgments. AD subgroup judgments did not differ for natural kinds compared to manufactured artifacts nor for words compared to pictures. AD subgroup differences could not be explained by dementia severity, memory, reading, and visuoperception. The similarity process for relating coordinate members of a taxonomic category contributes to the normal appreciation of word and picture meaning, and this process is compromised in AD patients with semantic difficulty.

Constraints on the cerebral basis for semantic processing from neuroimaging studies of Alzheimer's disease.

OBJECTIVE: Functional activation studies of semantic processing in healthy adults have yielded conflicting results. The purpose was to evaluate the relative role of the brain regions implicated in semantic processing with converging evidence from imaging studies of patients with impaired semantic processing. METHODS: Semantic memory was assessed in patients with Alzheimer's disease using two measures, and these performance patterns were related to profiles of reduced cerebral functioning obtained with high resolution single photon emission computed tomography (SPECT). Patients with frontotemporal degeneration were similarly evaluated as a control group. RESULTS: Reduced relative cerebral perfusion was seen in parietal and posterior temporal brain regions of patients with Alzheimer's disease but not patients with frontotemporal degeneration. Impairments on semantically guided category membership decision tasks were also seen in patients with Alzheimer's disease but not those with frontotemporal degeneration. Performance on the semantic measures correlated with relative cerebral perfusion in inferior parietal and superior temporal regions of the left hemisphere only in Alzheimer's disease. Relative perfusion was significantly lower in these regions in patients with Alzheimer's disease with semantic difficulty compared with patients with Alzheimer's disease with relatively preserved semantic processing. CONCLUSION: These findings provide converging evidence to support the contribution of superior temporal and inferior parietal regions of the left hemisphere to semantic processing.

Category-specific difficulty naming with verbs in Alzheimer's disease.

We studied 20 patients with Alzheimer's disease (AD) on a picture-naming task consisting of frequency-matched pairs of nouns and verbs that were homophonic and homographic (e.g., paint). Intragroup comparisons revealed that verb naming is significantly more difficult for patients with AD than noun naming. An error analysis demonstrated that patients with AD produce significantly more semantic and descriptive errors for verbs than nouns. We correlated verb naming and noun naming with measures of grammatical comprehension, lexical retrieval, and visuoperceptual processing, but there were no selective effects for verbs compared with nouns. Differences in the mental representation of concepts underlying verbs and nouns may account, in part, for the relative difficulty naming with verbs in AD.

Language comprehension profiles in Alzheimer's disease, multi-infarct dementia, and frontotemporal degeneration.

We assessed language functioning in 116 age-, education-, and severity-matched patients with the clinical diagnosis of Alzheimer's disease (AD), multi-infarct dementia (MID) due to small-vessel ischemic disease, or a frontotemporal form of degeneration (FD). Assessments of comprehension revealed that patients with AD are significantly impaired in their judgments of single word and picture meaning, whereas patients with FD had sentence comprehension difficulty due to impaired processing of grammatical phrase structure. Patients with MID did not differ from control subjects in their comprehension performance. Traditional aphasiologic measures did not distinguish between AD, MID, and FD. Selective patterns of comprehension difficulty in patients with different forms of dementia emphasize that language deficits cannot be explained entirely by the compromised memory associated with a progressive neurodegenerative illness.