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Poster E25, Thursday, August 22, 2019, 3:45 – 5:30 pm, Restaurant Hall

Individual differences in the neural organization of language, and their relationship to language abilities

Karla Rivera-Figueroa1, Michael C. Stevens2,3, Inge-Marie Eigsti1;1University of Connecticut, 2Olin Neuropsychiatry Research Center, The Institute of Living/Hartford Hospital, 3Yale University School of Medicine

Left hemisphere dominance for language functions has been well established. However, less is known about the impact of degree of lateralization on the fluency and efficiency of language processing. Typically developing adults are assumed to be fluent speakers of their native language, and effectively similar in their abilities. The current study takes an individual differences approach, examining the functional lateralization of language-specific regions in the brain, and testing whether degree of lateralization is associated with behavioral language skills in 19 healthy adults ages 18-21 years. Method. This study employed an fMRI adaptive semantic matching paradigm (Wilson, Yen, & Eriksson, 2018). 3T fMRI data were collected on a Prisma scanner and processed using the Human Connectome Project (HCP) pipeline. Language-related parcellations were selected based on prior work (Glasser et al., 2016) and divided into frontal and temporoparietal clusters. Participants completed behavioral assessments of vocabulary (PPVT and Stanford Binet-Verbal Knowledge; VKN), syntax (grammatical judgment task; GJ), and a non-verbal fluid reasoning task (Stanford Binet- Object Series/Matrices; NVIQ). Functional degree of lateralization indices (LIs) were computed using the formula LI= abs[(Aleft-Aright)/(abs(Aleft)+ abs(Aright))], where Aleft was the average activations from the fMRI general lineal model collapsed across vertices, within each pre-defined HCP parcel. A multiple regression analysis tested this relationship, including PPVT, VKN, GJ accuracy, and NVIQ as predictors. Results. The temporoparietal model was significant, F(4.925), p=0.014, such that higher behavioral task scores were associated with increased LI. The GJ task was a significant individual contributor to the model, p=0.005; PPVT approached significance, p=0.06. Adding non-verbal IQ (fluid reasoning) scores to the model did not improve the model, p=0.034, and IQ was not a significant individual predictor of laterality in this region. The frontal regression model was not significant, p=0.06, although PPVT and VKN scores were significant predictors in this model, p=0.021 and p=0.039, respectively; non-verbal IQ was again not a significant predictor. Discussion. Taken together, these scores suggest that greater degree of language specialization relative to homologous regions of the contralateral hemisphere in the temporoparietal area maps into better behavioral language skills in healthy adults with entirely normative language abilities. Both lexical/semantic knowledge (PPVT score) and syntactic processing (grammaticality judgment) contributed unique variance to the fMRI model, suggesting that this functional organization reflects enhanced language functioning across multiple linguistic domains; further, results were not driven by general cognitive ability . Results are consistent with findings of reduced lateralization (specialization) in individuals with developmental language disorders (Whitehouse & Bishop, 2008; Badcock et al., 2012; De Guibert et al., 2011; Herbert et al., 2002, Illingworth et al.,2009; Sun et al., 2010), suggesting that reduced language laterality may act as a risk factor that results in language impairments. Findings also provide a foundation for interpreting the neural reorganization observed in acquired language disorders.

Themes: Meaning: Lexical Semantics, Syntax
Method: Functional Imaging

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