Poster A4, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall
Parieto-temporal functional connectivity supports speech comprehension: Evidence from a stroke model
Lynsey Keator1, Grigori Yourganov2, Leonardo Bonilha3, Christopher Rorden2,4, Julius Fridriksson1,4;1Department of Communication Sciences and Disorders, University of South Carolina, 2Department of Psychology, University of South Carolina, 3Department of Neurology, Medical University of South Carolina, 4McClausland Center for Brain Imaging, University of South Carolina
Introduction: Auditory comprehension (AC) is often impaired after left hemisphere (LH) stroke. Traditional views propose Wernicke’s area (left posterior temporal cortex) is crucial for AC; however, current literature reveals a distributed LH network consistent with the dual-stream model of language processing (Hickok and Poeppel, 2007), where ventral-stream areas are implicated in language comprehension. Functional connectivity (FC) analysis, which measures the temporal synchrony of activation between brain regions, is a widely used method for studying cortical networks. In the current study, we analyze functional networks within the dual stream model in relation to AC in persons with aphasia (PWA) and introduce a novel approach to control for potentially confounding effects of lesion volume and impaired structural connectivity. Methods: Sixty-three PWA (25 women, mean age at stroke = 56.79 ± 12.74; mean months post stroke = 56.08 ± 59.77) were assessed with the Western Aphasia Battery-Revised (WAB-R; Kertesz, 2007) to determine aphasia type and severity. The same battery was used to assess AC. Structural (T1, T2), diffusion tensor imaging, and resting state fMRI scans were acquired and lesions were demarcated manually. FC for each pairing of cortical regions of interest (ROIs) was estimated as Pearson’s correlation coefficient between the mean BOLD time courses measured in those regions. NiiStat (https://github.com/neurolabusc/NiiStat) was used to analyze association between FC within dorsal and ventral stream ROIs and performance on the WAB, using a general linear model (GLM). ROIs were obtained by mapping ventral stream areas (Fridriksson et al., 2016) onto the segmentation specified by the AICHA atlas (Joliot et al., 2015), yielding 41 LH ventral stream ROIs, 26 dorsal stream ROIs and right-hemisphere homologues. We controlled for lesion size by regressing it out of the behavioral scores and controlled for structural connectivity by regressing out the fiber count between a pair of ROIs from the FC value for the same pair. 5000 permutations were performed to correct for multiple comparisons. Results: We identified several functional connections within the LH ventral stream (dorsal angular gyrus (and adjacent inferior parietal region) and middle temporal regions where decreased FC was associated with impaired AC. GLM Z-scores (measuring the strength of association between FC and AC scores) ranged between 3.7 and 4.6. Functional connections within LH dorsal-stream regions were not significantly correlated with AC scores nor were connections within right-hemisphere homologues of the ventral areas. Conclusion: Controlling for both lesion size and structural connectivity, we conclude these effects are not solely driven by damage to ROIs, frank damage to white matter connections between ROIs, or general behavioral impairment associated with larger lesions. Instead, poor AC correlates with a loss of synchrony in a broad posterior parieto-temporal network. These regions, independently, have been implicated in AC (Dronkers et al., 2004) and in consideration of the current body of literature, our findings emphasize AC is not localized to a single cortical region, but rather, a widely distributed network.
Themes: Disorders: Acquired, Methods
Method: Functional Imaging