Individualized functional localization of the language and multiple demand network in chronic post-stroke aphasia

Recent research found a distinct dissociation between brain regions supporting domain-general cognitive processes and regions supporting core language functions. The question of whether individuals with post-stroke aphasia (IWA) exhibit a comparable dissociation remains debated, particularly as previous studies overlooked individual variability in functional network organization and aphasia heterogeneity. To address this gap, we employed an individualized functional localization approach to test the involvement of the domain-general multiple demand (MD) network during language processing in chronic aphasia. We collected functional MRI data in 15 IWA and 13 age-matched controls. Participants performed a spatial working memory task, triggering MD network activation, as well as a listening and reading task, triggering language network activation. We compared both groups individualized activation patterns and investigated the link with aphasia severity. Involvement of the MD network during language processing was examined by investigating language task activity within subject-specific regions that are active during the MD task. The language and MD network each generalized well across different task modalities, but exhibited robust spatial dissociation from each other in both groups. Moreover, there was no evidence of MD network activation during language processing in either group. Additionally, the language network showed weaker activation in IWA compared to controls in left-hemispheric brain regions, with higher activation values in the left correlating with improved language performance in IWA. In conclusion, our findings suggest that the MD network does not contribute to passive, receptive language functions in chronic aphasia or healthy older adults. Instead, our results align with previous research proposing that normalized left-hemispheric language activity supports language performance in chronic aphasia.