Neural Correlates of Language Processing in Post-Stroke Aphasia
Schneck, Sarah Marie
We investigated functional reorganization for language processing in post-stroke aphasia, while making a concerted effort to ameliorate previously identified methodological challenges and implementing a novel method to disentangle the effects of structural damage and activation on behavior. Participants included 67 individuals with aphasia and 46 neurotypical comparison participants. A reliable and valid language mapping paradigm revealed that language processing remained left lateralized in people with aphasia. A whole brain direct comparison between groups revealed reduced activation in people with aphasia in left hemisphere language regions and the contralateral cerebellum. Activation was positively correlated with language performance in people with aphasia in similar left hemisphere language regions. Region of interest (ROI) analyses, involving individually defined ROIs in the bilateral inferior frontal cortex and posterior temporal cortex, revealed similar findings, and additionally showed reduced activation in the right posterior temporal cortex. We then used support vector regression to derive a structural predictor of performance and investigated whether activation was predictive of performance over and beyond what could be predicted by lesion information. In the whole brain analysis, activation in the left posterior temporal cortex was predictive over and beyond what could be predicted by lesion information. The more sensitive ROI analysis further showed that activation in the left inferior frontal cortex (p = .025) and the right posterior temporal cortex (p = .032) was also predictive over and beyond what could be predicted by lesion information; however, only activation in the left posterior temporal cortex was predictive over and beyond what lesion information and what the other meaningful ROIs could predict. In sum, our data are consistent with the claims that people with aphasia demonstrate reduced activation in left hemisphere language regions and continue processing language in spared left hemisphere language regions. We refined previous claims by providing evidence that the left posterior temporal cortex is the most critical region for language recovery. We found no compelling support for differential recruitment of the right hemisphere. However, there was some modest support for activation in the right posterior temporal cortex to be associated with performance.