Neural Predictors for the Generalization of Semantic and Phonological Treatment to Discourse Performance in Chronic Post-Stroke Aphasia.

Recovery of language function in post-stroke aphasia is affected by many variables, including aphasia severity, age, lesion site and size, and brain health. Semantic and phonological therapies are often used to target naming abilities, and when successful their benefits can extend to discourse production, which has emerged as a promising task to evaluate language processing and recovery in aphasia. Here, after characterizing the lesion and white matter integrity predictors for discourse production before treatment, we asked whether brain integrity at baseline is predictive of treatment generalization to discourse. In a large sample of participants with chronic aphasia (N = 88), we ran region-based lesion-symptom mapping on discourse measures (including fluency, sentence processing abilities, and error types) at baseline, on discourse changes following phonological and semantic treatment separately, and at 1 month and 6 months post-treatment. Discourse productivity at baseline was associated with the integrity of regions and white matter tracts in the dorsal stream. Lesions in the hippocampal system and cortical temporal regions were associated with less improvement in discourse following both phonological and semantic treatment. Long-term improvement was instead predicted by the integrity of the fornix and temporal cortical regions, suggesting that while the hippocampal system is important for learning, learned functions rely on connectivity with cortical areas. The results suggest that the generalization of word-level treatment to discourse production is facilitated by an intact hippocampal system in the medial temporal lobe.