NETWORK DYSFUNCTION IN POST-STROKE APHASIA

Recovery of language function after aphasic stroke is the product of activity in domain-general and domain-specific distributed brain networks. These may include left and right fronto-temporo-parietal, cingulo-opercular, and default mode networks. This functional MRI study investigated the effects of a previous left hemisphere stroke on brain activity during speech production in fifty-three patients. The results were related to twenty-four healthy participants. The analyses investigated not only local activity, but also functional connectivity both within and between distributed networks. Although activity within individual networks was not predictive of speech production, the relative activity between networks was a predictor of both within-scanner and out-of-scanner performance, over and above that predicted from lesion volume and various demographic factors. The specific imaging predictors were the differential activity between the default mode network and both the left and right fronto-temporo-parietal networks, respectively activated and deactivated during speech. These networks also showed altered between-network functional connectivity in patients. Therefore the systems neuroscience of recovery of function after focal lesions is not adequately captured by notions of brain regions ‘taking over’ lost domain specific functions, but is best considered as the interaction between what remains of domain-specific networks and the domain-general systems that regulate behaviour.