Naming and comprehension in primary progressive aphasia: The influence of grammatical word class

Background: Various clinical types of primary progressive aphasia have been associated with distinct areas of atrophy and pathological changes. Therefore, differences in the patterns of language deterioration in the various types might reveal the types of language processes and representations that depend on the areas of brain that are disproportionately affected. Aims: To test the hypotheses (1) that individuals with progressive nonfluent aphasia (associated with left posterior, inferior frontal, and insular atrophy) show progressive motor speech impairment and disproportionate deterioration in naming actions relative to objects, and (2) that individuals with semantic dementia (associated with anterior and inferior temporal atrophy) show disproportionate deterioration in semantic representations of objects relative to actions. Methods & procedures: The study population consisted of 56 participants with primary progressive aphasia, including 27 with progressive nonfluent aphasia, 16 with semantic dementia, and 13 with amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD). Participants were given tests of oral and written naming and tests of picture and word association with object and action stimuli. Differences across tests within each group were evaluated. Associations between motor speech impairment (based on a clinical motor speech examination) and naming impairment in each grammatical word class were evaluated. Outcomes & results: Participants with progressive nonfluent aphasia and ALS-FTD showed significantly more impairment in naming actions than objects. In contrast, participants with semantic dementia were significantly more impaired in naming objects than actions, and more impaired on semantic tests of objects relative to actions. In all groups, all participants who were more impaired in naming actions also had impaired motor speech (dysarthria and/or apraxia of speech). Conclusions: Distinct patterns of deterioration across grammatical word classes in these clinical subtypes were documented. Together with evidence that these clinical subtypes are associated with different areas of brain atrophy in other studies, our results are consistent with a role of posterior inferior frontal cortex and insula in motor speech and naming actions, as well as the essential role of anterior temporal lobes in semantic representation of objects.