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Poster D23, Thursday, November 9, 6:15 – 7:30 pm, Harborview and Loch Raven Ballrooms

Language pathway development requires childhood language acquisition: Effects of sensorimotor modality and language deprivation on brain connectivity for language

Qi Cheng1, Eric Halgren1, Rachel Mayberry1;1University of California, San Diego

Long-range white matter fiber tracts play an important role in establishing the dynamic and distributed language network. Previous research on spoken languages had identified two information streams that are crucial for language processing, namely the ventral and dorsal pathways. The dorsal pathway consists of the superior longitudinal fasciculus (SLF) - arcuate fasciculus (AF) complex, connecting the inferior frontal gyrus (IFG) with the superior temporal gyrus/sulci (STG/STS) and the inferior parietal lobule (IPL). Ventral pathways include the inferior fronto-occipital fasciculus (IFOF), the inferior longitudinal fasciculus (ILF), and the uncinate fasciculus (UF). American Sign Language (ASL) activates very similar brain regions such as the STG/STS and the IFG, despite differences in sensorimotor modality. No study to date has examined the effect of sensorimotor modality on brain connectivity for language processing. Previous studies on deaf brain connectivity showed inconsistent findings, likely due to the variability of deaf population of their language acquisition and use. Deaf people with hearing parents often experience early language deprivation, which may affect their brain connectivity. The current study investigates the effect of sensorimotor modality and language acquisition history by examining the white matter connectivity of the dorsal and ventral pathways among congenitally deaf people with or without early access to American Sign Language (ASL). Diffusion data were acquired using a GE 1.5 Tesla scanner and preprocessed following standard steps. We identified dorsal pathways AF and posterior SLF (pSLF), and ventral pathways IFOF, ILF, and UF, using an automated tract atlas. Next we calculated the average fractional anisotropy (FA) value of each tract of interest in each hemisphere. For Study 1, we recruited 12 hearing people and 12 deaf native signers to determine if the two groups show similar ventral and dorsal language pathways. In Study 2, we examined the language tracts of three deaf individuals who experienced minimal language until adolescence or adulthood, two adolescents who were at the initial stage of language learning, and one adult who had completed his (limited) language acquisition. The results indicate that individuals born deaf with infant language experience have language tracts that are not different from hearing controls. Both groups show left lateralization and a similar range of FA values. By contrast, all three cases of extremely late L1 exposure demonstrated significantly lower FA values for the left AF tract compared with the deaf native group, but not for other tracts including pSLF, IFOF, ILF and UC, where the FA values were generally within a normal range. These findings indicate that auditory deprivation and the sensorimotor modality of language do not affect the white matter connectivity between language regions. However, childhood language deprivation alters white matter connectivity, especially in the dorsal AF pathway. This is apparent for individual adolescents in the early stages of language acquisition, as well as for the adult with more than 20 years of ASL experience. Our findings indicate that growth of the brain language pathways are not solely driven by biological maturation but require language acquisition during childhood to connect in the expected fashion.

Topic Area: Signed Language and Gesture

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