Auditory-verbal analysis in aphasia

Abstract

ABSTRACTBackground: Comprehension deficits are more pervasive in aphasic syndromes than initially believed. They affect differentially distinct levels of auditory-verbal comprehension. Current evidence from functional imaging studies in healthy subjects indicates that distinct levels of auditory-verbal analysis involve specific networks.Aims: The aim of this study is (1) to assess the different levels of auditory-verbal analysis with real-time monitoring tasks in patients with aphasia, (2) to compare the performance profiles across aphasia types, (3) to analyse patterns of dissociations vs. co-occurrence at specific levels, and (4) to establish correlations between disturbances at specific levels of auditory-verbal analysis and sites of lesions.Methods & Procedures: Forty-two right-handed patients with aphasia associated with a first unilateral left-hemispheric lesion underwent tests monitoring (1) phonetic-phonological, (2) lexical, (3) morphosyntactic, (4) semantic-pragmatic (at sentence level), and (5) linguistic prosody processing. Anatomo-clinical correlations were established by means of voxel-based lesion-symptom mapping.Outcomes & Results: Widespread deficits at multiple levels occurred across aphasic syndromes. In a given patient, more levels tended to be impaired in Wernicke’s and global aphasia than in Broca’s or conduction aphasia. Syllable and word processing double-dissociated behaviourally and partially anatomically. Morphosyntactic deficits were always accompanied by semantic-pragmatic deficits. Anatomo-clinical correlations implicated the dorsal auditory stream in syllable discrimination, the ventral stream in semantic processing at lexical level and in linguistic prosody and both streams in lexical frequency effect. Basal ganglia were implicated in syntactic and semantic processing at sentence level.Conclusions: At prelexical and lexical levels, syllable and word processing appear to be independent of each other. At sentence level, parsing of syntactic structure appears to be necessary for successful semantic-pragmatic analysis. Thus, the fine-grained evaluation of auditory-verbal processing capacities and of the integrity of specialised processing networks in brain-damaged patients provides a sensitive diagnostic tool.