Xueying Ren¹ (), James R. Booth¹, Gabriele Amorosino², Franco Pestilli², Sophia Vinci-Booher¹; ¹Vanderbilt University, ²The University of Texas at Austin

Visual processing regions in the ventral temporal cortex connect directly to the parietal cortex via the posterior vertical pathway (PVP), yet the development of its white matter tracts and their relationship with learning, particularly during periods of rapid change, is poorly understood. This pre-registered study (https://osf.io/97ybe) used a dense longitudinal neuroimaging design to capture rapid and potentially nonlinear changes in the microstructure of PVP tracts throughout the first grade, a year of foundational learning. We collected diffusion MRI and behavioral assessments of number processing and word processing from ten first-grade children every month for 12 months. First, regarding the behavioral data, we identified nonlinear changes in learning throughout the first year of schooling. Then, we used a time series approach to model the temporal relationships among brain structures at the start and ongoing brain and behavioral changes observed throughout the year. Contrary to our expectation, we did not find a relationship between the posterior Arcuate (pArc) and word processing. Instead, we found that month-to-month changes in fractional anisotropy (FA) in the right Middle Longitudinal Fasciculus (MDLF)—specifically the connections to the Angular Gyrus (MDLF-Ang) and Superior Parietal Lobe (MDLF-SPL)—positively predicted month-to-month changes in number processing, but not word processing. This captures an ongoing coupling between brain change and learning. Also, this temporal relationship was underpinned by changes in orientation dispersion (ODI), indexing axonal organization. Our results demonstrated that rapid changes in at least one of the microstructure of PVP tracts occurred alongside rapid changes in number processing during a relatively short critical window of foundational learning, suggesting a dynamic and ongoing interplay between brain and behavioral change.

Acknowledgements: Funding: R01 HD114489