Yongning Lei¹ (), Pedro M. Paz-Alonso^1,2, Garikoitz Lerma-Usabiaga^1,2; ¹Basque Center on Cognition, Brain & Language, ²Ikerbasque, Basque Foundation for Science, Bilbao, Bizkaia, Spain

Reading is a rapid process. Within hundreds of milliseconds, perceptual input from the eyes is integrated by the early visual cortex and processed by higher-order visual and language networks, including the ventral occipitotemporal cortex (vOTC) and the inferior frontal gyrus (IFG). Electrophysiological evidence has shown that the IFG becomes active during reading within 200 milliseconds. This early-stage activation suggests the presence of direct white-matter connections between visual territories and the IFG. Previous research has identified four major white-matter tracts linking the vOTC and IFG, however, the detailed connectivity profiles between subregions of these visual and language circuits remain poorly characterized, partly due to the limitations of diffusion-weighted imaging (DWI). In this study, we used a high-quality diffusion MRI dataset (N=66, plus 31 retested) to investigate white-matter connectivity patterns between subregions of the ventral visual pathway and the IFG (pars opercularis, triangularis and orbitalis). To address methodological challenges, we applied a novel approach combining two tract reconstruction algorithms: ROI-to-ROI streamlines and whole-brain tractography. This approach allowed us to delineate subregion-specific white-matter connections without compromising their anatomical accuracy. Our results revealed that the pars opercularis is primarily connected to the anterior vOTC dorsally via the arcuate and superior longitudinal fasciculi. In contrast, the pars orbitalis exhibited exclusive ventral connectivity to the vOTC through the inferior fronto-occipital and inferior longitudinal fasciculi. The pars triangularis displayed a mixed connectivity pattern, with the posterior vOTC connecting ventrally and the anterior vOTC dorsally. In sum, our findings provide a detailed characterization of the structural connectivity underlying reading networks, offering a framework for exploring the white-matter connectivity and functional connectivity, and providing insights into the computational theories of reading.

Acknowledgements: BCBL acknowledges the support of the Basque Government through the BERC 2022-2025 program and Funded by the Spanish State Research Agency through BCBL Severo Ochoa excellence accreditation CEX2020-001010/AEI/10.13039/501100011033