Multi-modal and task-modulated inter-hemispheric connectivity changes after left arcuate resection
Benjamin Chernoff1, Alexander Teghipco1, Frank Garcea1,2, Max Sims1, Susan Smith3, Webster Pilcher3, Bradford Mahon1,2,3,4; 1Department of Brain & Cognitive Sciences, University of Rochester, USA, 2Center for Visual Science, University of Rochester, USA, 3Department of Neurosurgery, University of Rochester Medical Center, USA, 4Department of Neurology, University of Rochester Medical Center, USA
Lesions to the left arcuate fasciculus can cause conduction aphasia—impaired repetition of speech with intact comprehension and spontaneous speech. However, there is ongoing debate about whether the damage to the left arcuate fasciculus is sufficient to cause conduction aphasia, and it is unknown why conduction aphasia is often observed to be a transient phenomenon. The role of the right hemisphere in recovery from aphasia also remains an active area of study. Here we report a comprehensive case study of patient AH, who underwent resection of a temporal-parietal tumor that had infiltrated the left arcuate fasciculus. AH exhibited conduction aphasia intra-operatively as well as a transient global aphasia immediately after surgery, which resolved into a conduction aphasia that lasted for several weeks. We studied AH longitudinally using structural and functional MRI before and after surgery. We observed that there was a reduced intra-hemispheric functional connectivity in the left hemisphere post-operatively compared to pre-operatively; in contrast, there was increased inter-hemispheric connectivity increased post-operatively compared to pre-operatively. These patterns were observed only for task-based language tasks, and were not observed for task-based non-language tasks. Using probabilistic tractography with atlas-defined ROIs, we observed a significant decrease in structural connectivity between left Broca’s and Wernicke’s areas post-operatively compared to pre-operatively. Those measures of structural connectivity were within the distribution of 52 healthy age-matched control subjects pre-operatively, but outside the distribution post-operatively. These findings have important implications for understanding how inter-hemispheric connectivity may interact with functional reorganization of the language system after left hemisphere injury.
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