Behavioral constructs and neural correlates of descriptive and responsive speech in post-stroke aphasia.

Discourse refers to language that extends beyond a single clause and is used to express ideas, feelings or to interact with others. Persons with post-stroke aphasia often encounter difficulties in discourse, which can severely impede everyday communication. In recent years, discourse has received more attention in both research and clinical practice due to its high ecological validity. However, little is known about the underlying behavioral constructs and neural correlates of discourse in post-stroke aphasia. In the current study, discourse was assessed in 49 persons with chronic aphasia following left-hemispheric (n = 39) or bilateral (n = 10) stroke using picture description from the CAT (descriptive speech) and verbal responses to everyday scenarios from the ANELT (responsive speech). Factor analysis and voxel-wise lesion symptom mapping were performed to investigate the underlying behavioral and neural constructs. Factor analysis revealed four latent constructs that explained 64% of the total variance in the discourse variables: grammatical, phonological, lexical-semantic and macrostructural. Fluency variables were spread across these four different factors. For example, digression was associated with word repetitions and filled pauses, while grammatical deficits were associated with speech rate and long pauses. After correction for multiple comparisons, only the lexical-semantic factor was significantly associated with a left cluster covering lesions in the inferior parietal, superior and middle temporal and lateral occipital regions. In conclusion, this study shows that discourse analysis can reveal both clustered and distributed dimensions and further establishes the role of the left inferior parietal and superior and middle temporal lobe in lexical-semantic abilities.