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Thalamic changes in gray- and white-matter over the lifespan related to language development
Poster E90 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Leandro Lecca-Villacorta1, Garikoitz Lerma-Usabiaga1,2, Pedro M. Paz-Alonso1,2; 1Basque Center on Cognition, Brain and Language, 2Ikerbasque, Basque Foundation for Science, Bilbao, Spain
Language development is a complex phenomenon shaped by a confluence of neurobiological, cognitive, and environmental factors (Pulvermüller & Schumann, 1994; Romeo, 2019). Language undergoes dynamic changes across an individual’s lifespan, leading to the organization and specialization of its constituent systems within the brain. For instance, language acquisition initially involves bilateral engagement before transitioning to a state of left-hemisphere dominance (Olulade et al., 2020). A wealth of research findings have consistently highlighted the preferential involvement of left-hemispheric regions in language processing, but emerging evidence suggests that thalamic asymmetry may also contribute to language functions and lateralization (Hebb & Ojemann, 2013). Understanding age-related changes in thalamic organization is crucial as modern accounts emphasize the role of the thalamus in modulating information flow in higher-order cognitive processes, including language (Klostermann et al., 2013). However, investigations into the volumetric changes of thalamic nuclei and the development of thalamocortical bundles across the lifespan are limited. Here, we sought to characterize changes in both thalamic nuclei volume and thalamocortical white-matter tracts over the lifespan. Our cohort consists of 348 healthy right-handed individuals spanning from middle childhood to senescence (age range: 6.4 to 81.6, mean age: 39.21 ± 23.9 years; 194 females, 154 males). T1-weighted (T1w) images were processed with the Freesurfer software package, and thalamic segmentation was refined by the first probabilistic atlas of the human thalamic nuclei combining ex vivo MRI and histology (Iglesias et al., 2018). Diffusion-weighted images (DWI) were denoised, corrected for anatomical distortions, and registered to T1w images, using the preprocessing pipeline provided in the Reproducible Tract Profiles 2 (RTP2) (Lerma-Usabiaga et al., 2023). Finally, white-matter thalamocortical tracts were reconstructed and measured using the RTP2-pipeline for both first-order and higher-order human thalamic nuclei (Liu et al., 2022), ensuring neuroanatomical reproducibility and data provenance. Our findings demonstrate that almost all thalamic nuclei exhibited a shrinking trajectory over the lifespan. Remarkably, the trajectories of asymmetry indices reflected a rightward volumetric lateralization that persists over the lifetime, with the right thalamus following different shrinking developmental profiles with respect to the left thalamus. Notably, higher-order nuclei tend to exhibit an increasing rightward asymmetry from childhood to adulthood which reverts in the posterior years, while first-order nuclei show subtle or no interhemispheric differences across the lifespan, possibly influenced by the strong bilateral dependency of sensory and motor functions. These results, combined with micro and macro-structural measures of thalamocortical white-matter projections (Mean Diffusivity, Fractional Anisotropy, Apparent Fiber Density, and DICE), suggest a heightened level of remodeling within the left thalamus. This phenomenon is likely attributed to the influence of cognitive functions that are strongly left-lateralized and remain relatively intact in healthy aging, such as language. For the first time, our work provides a comprehensive view of structural developmental patterns of the human thalamic nuclei and thalamocortical tracts and discusses their developmental trajectories in relation to language.
Topic Areas: Language Development/Acquisition, Computational Approaches