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Cerebro-cerebellar pathways contribute to written language production
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Poster D128 in Poster Session D, Wednesday, October 25, 4:45 - 6:30 pm CEST, Espace Vieux-Port
Romi Sagi1, Sivan Jossinger1,5, J.S.H. Taylor2, Kyriaki Neophytou3, Brenda Rapp3, Kathleen Rastle4, Michal Ben-Shachar1; 1Bar-Ilan University, 2University College London, 3Johns Hopkins University, 4The Royal Holloway, 5Functional MRI Center, Beilinson Hospital
Producing language is a highly complex human skill involving a distributed network of brain regions. Written language production constitutes a part of our everyday communication, but the neural pathways that support it are relatively understudied. The current study examines the pathways associated with language production in its written form. For spoken language production, studies have demonstrated the involvement of bilateral cerebro-cerebellar pathways and of the bilateral frontal aslant tract (FAT), which connects the inferior frontal gyrus (IFG) with the supplementary motor area (SMA) (Jossinger et al., 2023). The cerebellum, IFG, and SMA have also been implicated in a few fMRI and lesion studies of writing (Purcell et al, 2011; Planton et al., 2013; Paul et al., 2022). However, the pathways connecting these regions are yet to be studied in the context of written language production. Here, we aim to assess the contribution of the cerebro-cerebellar pathways and the FAT to spelling performance. 73 English-speaking neurotypical adults (mean age: 21y±2.7, 57 females) underwent a typed spelling-to-dictation task, to assess their written spelling accuracy. To avoid a ceiling effect, stimuli consisted of long, low-frequency words, with one-to-many phoneme to grapheme mappings. Imaging data were acquired on a 3T Siemens scanner, using a diffusion-weighted, single-shot EPI sequence (64 diffusion directions at b=1000 and 1 volume at b=0 s/mm^2, voxel size: ~2*2*2mm^3). Two pipelines were used to preprocess diffusion MRI data: (1) constrained spherical deconvolution modeling coupled with probabilistic tractography, and (2) tensor modeling coupled with deterministic tractography. The bilateral cerebro-cerebellar pathways and FAT were identified in individual participants using automated tools. Fractional anisotropy (FA) values were calculated along each tract, and Spearman’s correlations were calculated between spelling accuracy scores and FA. Spelling accuracy scores were widely distributed across individuals, ranging between 7% to 97% correctly spelled items. We found a significant correlation between spelling accuracy scores and FA in the left cerebro-cerebellar pathway, such that higher FA values were associated with higher spelling accuracy scores. This finding was consistent across both preprocessing methods. Specifically, we detected a significant correlation with spelling accuracy in a large portion of the left cerebro-cerebellar tract (pipeline 1, N=65, r=.38, p<.05, family-wise error corrected). Similarly, spelling accuracy was correlated with the mean tract-FA of the left cerebro-cerebellar tract (pipeline 2, N=73, r=.26, p<.05, uncorrected). No significant correlations were found between spelling accuracy scores and FA in the bilateral FAT, nor in the right cerebro-cerebellar pathway. The current findings demonstrate, for the first time, the involvement of cerebro-cerebellar connections in spelling processes. According to a dominant view, the cerebellum encodes internal models, corresponding to neural representations of the external world (Wolpert, 1998). By interacting with the cerebral cortex through cerebral-cerebellar loops, cerebellar internal models can be utilized to simulate mental representations, such as the orthographic and phonological representations essential for accurate spelling. Future studies will further isolate the specific components of the spelling process mediated by the cerebro-cerebellar pathways.
Topic Areas: Writing and Spelling,