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Lesion-based evidence that top-down connections from the language network support posterior visual word form area function
Poster Session B, Friday, September 12, 4:30 - 6:00 pm, Field House
Sara Dyslin1, Andrew DeMarco1,2, Ryan Staples1,3, Peter Turkeltaub1,2,4; 1Center for Brain Plasticity and Recovery, Georgetown University, 2Center for Aphasia Research and Rehabilitation, Georgetown University, 3Georgetown-Howard Universities Center for Clinical and Translational Science, Georgetown University, 4MedStar National Rehabilitation Hospital
Reading relies on a region of the brain’s object recognition system in the ventral occipito-temporal cortex (vOTC) that becomes specialized for word recognition with literacy: the visual word form area (VWFA). Prior fMRI studies in neurotypical adults have proposed a posterior-to-anterior gradient in the VWFA, reflecting increasing sensitivity to larger orthographic units, and suggest that the VWFA is shaped by top-down input from the language network. Lesions to left perisylvian language regions frequently result in alexia, possibly due in part to network-level disruptions of top-down support to the intact VWFA. However, this has not been directly tested. While right hemisphere (RH) homologues of language regions can be recruited after left hemisphere (LH) stroke, it remains unknown whether the RH homotope of the VWFA (rVWFA) contributes to reading post-stroke. This study examined how LH language network lesions affect the localization and magnitude of VWFA activity in left and right vOTC during reading. Participants included 30 chronic LH stroke survivors (LHSS) without VWFA lesions (Age=60.9(14.6); Gender=11F/19M; Months-since-stroke=56.7(56.1); Lesion Volume=67.2cm³(70.8); WAB-AQ=86.1(13.3)) and 38 demographically-matched controls. All participants completed three runs of a novel block-design fMRI task involving rapid serial visual presentation of words, pseudowords, false fonts, or fixation. Word > false font contrasts were analyzed for each individual, and then entered into a mixed-effects model. A LH VWFA mask was derived from Neurosynth, then subdivided into anterior and posterior regions, and mirrored onto the RH. For each ROI, the top 10% of activated voxels were used to calculate activation magnitude and center-of-mass location for each participant. Regression analyses assessed the effects of group (patient/control), hemisphere (left/right), and subregion (anterior/posterior) on activation magnitude and localization along the anterior-posterior axis. Covariates included age, education, handedness, and lesion volume. A main effect of hemisphere revealed that both LHSS and controls showed relatively less activation in the whole rVWFA relative to the lVWFA (t(128)=-7.82; p<0.001). This effect held for both anterior and posterior subregions (p<0.001). Further, LHSS demonstrated significantly reduced activity in the posterior lVWFA relative to controls (p<0.001), which drove significant group-by-subregion interactions when comparing posterior lVWFA vs posterior rVWFA (p=0.01), and posterior lVWFA vs anterior lVWFA (p=0.001). Regression analyses predicting y-coordinates of peak activation within the whole lVWFA confirmed that peak activation was farther anterior in LHSS relative to controls (t(62)=2.48; p=0.015). An exploratory analysis of five additional LHSS with lesions to the lVWFA provided preliminary evidence of both decreased activation in the lVWFA and increased activation in the rVWFA, relative to both control and non-VWFA lesioned LHSS. These findings provide new lesion-based evidence that top-down connections from the language network support typical VWFA function. LH strokes that spare the VWFA can result in a decrease in posterior lVWFA activation. We hypothesize that disconnections from specific language regions may underlie these effects. Next steps include testing this hypothesis using lesion-symptom mapping methods, and determining how deactivation of posterior lVWFA affects reading outcomes after stroke. This information will be essential to understand adaptive reorganization of the VWFA, potentially including recruitment of the rVWFA.
Topic Areas: Reading, Disorders: Acquired