Progressive aphasic syndromes: clinical and theoretical advances

Knowledge of the neural basis for language and related aspects of cognition has been advanced through detailed studies of patients with primary progressive aphasia. This brief review highlights some recent work.

The impairment of semantic knowledge in patients with semantic dementia appears to influence performance in a wide variety of linguistic and cognitive domains, including morphological agreements such as the irregular past tense. Computational studies modeling the deficits of these patients have advanced interpretations of the impairments in semantic dementia. Imaging analyses have confirmed the presence of temporal atrophy cross-sectionally and longitudinally in these patients. In patients with semantic dementia, it appears that both the left temporal and right temporal regions contribute in different proportions to naming and comprehension, although the nature of the process underlying the consolidation of knowledge in semantic memory continues to be actively debated. In patients with progressive non-fluent aphasia, recent work has emphasized an impairment with verbs. Functional neuroimaging work with progressive non-fluent aphasics, compared directly to non-aphasic patients with frontotemporal dementia, has demonstrated a dissociation for grammatical and working memory aspects of sentence processing within the left frontal cortex.

These findings will improve diagnostic accuracy, prognostic ability, and therapeutic potential in patients with progressive aphasia.