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Neural Network Bases of Thematic Semantic Processing in Language Production

Poster D60 in Poster Session D with Social Hour, Friday, October 7, 5:30 - 7:15 pm EDT, Millennium Hall

Deena Schwen Blackett¹, Jesse Varkey¹, Janina Wilmskoetter¹, Rebecca Roth², Keeghan Andrews¹, Natalie Busby³, Ezequiel Gleichgerrcht¹, Rutvik Desai³, Nicholas Riccardi³, Alexandra Basilakos³, Lorelei Phillip Johnson⁴, Sigfus Kristinsson³, Lisa Johnson Norris³, Chris Rorden³, Leigh Ann Spell³, Julius Fridriksson³, Leonardo Bonilha²; ¹Medical University of South Carolina, ²Emory University, ³University of South Carolina, ⁴Carolinas Rehabilitation

Semantic processing is a central component of language. The dual hub hypothesis proposes a neuroanatomical dissociation between taxonomic processing in the anterior temporal lobe (ATL) and thematic processing in the temporoparietal junction (Schwartz et al., 2011). However, other studies suggest a role of the ATL in thematic processing also (Teige et al., 2019). These regions may act together in a network linking the ATL with posterior structures to support thematic processing during language production. However, prior investigations of thematic processing focus on grey matter. This study investigates whether the integrity of white matter connections post-stroke is associated with the production of thematic errors during naming. Seventy-nine English-speaking adults with chronic aphasia (≥ 12 months post-stroke) completed the Philadelphia Naming Test (PNT; Roach et al., 1996). Participants were excluded if they had profoundly limited speech or auditory comprehension, bilateral or right-hemisphere stroke, or other brain injuries. Taxonomic and thematic error scores were measured by calculating the proportion of taxonomic or thematic errors out of total errors on the PNT. Inter-rater reliability was 94%. Whole-brain T1-weighted, T2-weighted, and echo-planar images were acquired. Manually drawn lesions were mapped into standard space and participant connectomes were reconstructed. Before performing connectome-based lesion-symptom mapping (CLSM; Gleichgerrcht et al., 2017), we residualized taxonomic and thematic error rates to remove shared variance between error types and control for semantic comprehension abilities via the Pyramid and Palm Trees Test (Howard & Patterson, 1992). Univariate and multivariate CLSM were then performed on 20 left-hemisphere regions to examine the relationship between white matter connection strength and residualized taxonomic and thematic error rates. A Wilcoxon signed-rank test showed that participants produced significantly more taxonomic than thematic errors on the PNT (z = -6.12, p < .001; M: 5.4 taxonomic, 2.7 thematic). Univariate CLSM revealed two white matter connections that were significantly associated with residualized thematic error scores, controlling for lesion volume: connections between the 1) pole of the middle temporal gyrus and posterior cingulate gyrus (PCG), and 2) inferior temporal gyrus (ITG) and insula. Multivariate CLSM revealed a model with 28 connections, including the two mentioned above, significantly predicting residualized thematic error scores above chance (r = .232, p = .02). No white matter connections were significantly associated with the residualized taxonomic error scores in either analysis. Behavioral results showed that participants produced more taxonomic than thematic errors, which has been reported previously in aphasia (Schwartz et al., 2011). The PCG has been linked to spatial/action semantic processing (Barrett et al., 2019). Therefore, the connection between the temporal pole and PCG may represent integration of action/event information with transmodal semantic representations in the ATL. The ITG is associated with semantic processing (Binder et al., 2009), and the insula may be involved in language, but its exact role in semantics is unclear (Ardila et al., 2014). Our data suggest these two areas and the connection between them could be involved in thematic processing. These results indicate that thematic processing is supported by an anteroposterior network involving several regions, including cortex outside temporoparietal region.

Topic Areas: Meaning: Lexical Semantics, Disorders: Acquired