Cerebral perfusion in post-stroke aphasia and its relation to residual language abilities

Stroke alters blood flow to the brain resulting in tissue loss. However, the disruption of cerebral blood flow (perfusion) can also be observed in surrounding tissue as well as distal areas. These structurally preserved but sub-optimally perfused regions may contribute less to recovery; thus, to better understand aphasia recovery the relationship between cerebral perfusion and language needs to be systematically examined. In the current study, we aimed to evaluate 1) how stroke affects perfusion outside of lesioned areas in chronic post-stroke aphasia, and 2) how perfusion in specific cortical areas and perilesional tissue relates to language outcomes in aphasia. We analyzed perfusion data from 43 participants with chronic aphasia due to left hemisphere stroke and 25 age-matched healthy controls. We used anatomically defined regions of interest that covered the frontal, parietal, and temporal areas of the perisylvian cortex in both hemispheres, along with several control regions, not implicated in language processing. For the aphasia group we also looked at three bands of perilesional tissue around the lesion. We compared perfusion levels between the two groups and investigated the relationship with between perfusion levels and language subtest scores while controlling for age, gender, time post-onset, scanning site, lesion volume, and lesion site. First, we observed that perfusion levels were significantly reduced in frontal and parietal areas in the left hemisphere in aphasia compared to the control group, while no differences were observed for right hemisphere regions. Second, we found that perfusion in the left temporal lobe (and most strongly in the posterior part of both superior and middle temporal gyri) and inferior parietal areas (supramarginal gyrus) was significantly related to residual language abilities. In contrast, perfusion in the frontal regions did not show such a relationship; no relationship with language was also observed for perfusion levels in control areas and all right hemisphere regions. Levels of perilesional perfusion were only marginally related to language production abilities. Cumulatively, the current findings demonstrate that blood flow is reduced beyond the lesion site in chronic post-stroke aphasia and hypoperfused neural tissue in critical temporo-parietal language areas may not be fully able to support recovery. These results underscore the critical and general role that left hemisphere posterior temporal regions play in various expressive and receptive language abilities. Overall, the study shows that slowed or reduced blood distribution can affect the functionality of regions beyond the lesion site and have a direct impact on behavioral outcomes. ### Competing Interest Statement The authors have declared no competing interest.