Neural Substrates of Phonological Processing in Chronic Aphasia from Stroke

Deficits in phonology are among the most common and persistent impairments in aphasia after left hemisphere stroke, and can have significant functional consequences for spoken and written language. While many individuals make considerable gains through physiological restitution and in response to treatment, the neural substrates supporting phonological performance in the face of damage to critical language regions is poorly understood. To address this issue, we used BOLD fMRI to measure regional brain activation in a case series of individuals with aphasia after left MCA stroke during a phonological task. The results of this study support the idea that damage to even a portion of the phonological network results in impaired phonological processing. We found that individuals with left perisylvian damage tend to rely on the residual left-hemisphere language network, and typically recruit regions associated with domain-general cognitive processing which fall outside of the left-hemisphere language network. However, recruitment of these regions did not necessarily enhance phonological processing. Rather, more successful phonological processing outside the scanner was associated with recruitment of a language region in right posterior middle temporal gyrus and a region in left occipital pole. More successful phonological processing inside the scanner was associated with additional recruitment of the left supramarginal gyrus within the healthy control network, engagement of bilateral intraparietal sulcus from the multi-demand network, and up-regulation of the right-hemisphere network of regions homotopic to the left-hemisphere language network seen in the healthy control group. These findings emphasize the contributions of residual components of the left-hemisphere language network, engagement of a non-linguistic domain-general multi-demand network, and the participation of the non-dominant right-hemisphere language network in successful phonological processing in chronic aphasia after stroke