Lesion-Induced Changes to the Network Controllability of the Right Pars Triangularis in Aphasia

Left hemisphere stroke causes functional changes to the language network and may shift aspects of language processing to right hemisphere homotopes of perisylvian language regions. The result of right hemisphere recruitment is unclear. Studies suggest the right pars triangularis (rPTr) engagement in language processing corresponds to higher dysfunction. As a result, the region is a site for inhibitory neuromodulation, with evidence that inhibiting the region improves language function in persons with aphasia (PWA). However, studies have also found no relationship between rPTr functional activity and language performance in PWA. The mixed evidence regarding the rPTr suggests additional work is needed to understand the role of the region in PWA. We propose that the white matter connections that support communication between regions may be an important mediator. Thus, we sought to investigate if left hemisphere stroke leads to changes in the structural topological properties of the region. We used measures from network control theory (NCT) to compare the theoretical capacity of the rPTr to integrate communication across brain modules (i.e., boundary controllability [BC]) in the brain, in 60 PWA and 62 controls. We also examined whether BC corresponded to different aspects of language processing (i.e., semantic and phonological) in PWA. We found that PWA had a higher BC in the rPTr relative to controls. Higher BC was associated with fewer phonological errors in a picture naming task. These findings suggest that left hemisphere stroke causes shifts in the structural role of right hemisphere regions that relate to language processing in PWA.