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Poster B7, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall

Resting state functional connectivity changes in transient post-operative aphasia

Christian Alexander Kell1, Laura Hansmeyer1, Marie-Therese Forster1, Ines Kropff1, Silke Fuhrmann1, Pavel Hok1,2, Johann Philipp Zöllner1;1Goethe University Frankfurt, 2Palacký University of Olomouc, Czech Republic

Aphasia results from a dysfunctional language network in the speech-dominant hemisphere. Compared to matched controls, aphasic stroke patients over-recruit right homologous brain regions and re-lateralize language-related activity to the left hemisphere in the course of recovery (Saur et al., 2006, Hartwigsen et al., 2013). However, stroke research does not provide the opportunity of comparing the aphasic and recovered state with a prelesional asymptomatic state in individual patients. This is a prerequisite to identify recovery-related neuroplasticity as normalization of peri-lesional functional connectivity. We studied transient aphasia following tumor surgery (Wilson et al., 2015) in patients who did not show language deficits presurgically. We analyzed changes in fMRI resting state functional connectivity associated with the development of and recovery from transient aphasia, which identifies task-independent network signatures. Repetitive resting state fMRI measurements were performed in 20 well-characterized patients undergoing awake tumor surgery of their speech-dominant left temporal (n=13) or left frontal (n=7) lobe. None had lasting speech or language symptoms prior to surgery and transient postoperative aphasia was present in all patients. Patients were assessed and measured before surgery, during maximal aphasia in the postoperative week and six months later. fMRI datasets were analyzed separately in the two groups (frontal/temporal tumor resection) using a seed-based whole brain functional connectivity analysis with six seeds in a priori defined language regions that were not directly affected by the tumor (inferior frontal gyrus pars triangularis, pars opercularis, articulatory motor cortex, dorsal premotor cortex, superior parietal-temporal area, superior temporal sulcus) and their contralateral homologues. Paired t-tests comparing functional connectivity between the three time points were significant at p<0.05 (FWE-corrected at cluster level, cluster-forming threshold of p<0.001, uncorrected). Because all tumor tissue / resection sites were masked out of the results to exclude spurious findings based on structural changes, connectivity between the left frontal and temporal lobe could not be assessed. In transient aphasia, the left dorsal premotor cortex/pre-SMA reduced resting state functional connectivity with the left inferior frontal gyrus. In addition, connectivity between the left superior temporal sulcus and the left precuneus, which is an important hub of the default mode network, was reduced. Transient aphasia was also associated with reduced interhemispheric resting state functional connectivity between left language areas and their homologues. Recovery from aphasia went along with a quasi-normalization of resting state functional connectivity, because only connectivity between the left primary articulatory motor area and the right planum temporale increased when comparing recovery with pre-surgery measurements. No other connection showed significant changes between pre-surgical and long-term measurements. Our results demonstrate that aphasia is indeed associated with reduced coupling of the left language network and reduced interhemispheric connectivity, even in the absence of overt language processing. This observation could reflect alterations of inner speech during aphasia, particularly because Wernicke’s area coupled less strongly with the introspection-related default mode network during rest. Recovery was rather related with a return to baseline connectivity than with large-scale re-organization of language networks, indicating local neuroplasticity could be key in restoring language function in the distributed speech and language network.

Themes: Disorders: Acquired, Language Production
Method: Functional Imaging

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