Region-dependent mechanical parameters in simulating cerebral atrophy.

Brain aging and atrophy involve complex multiscale factors of cellular degeneration and morphological changes. Although previous biomechanical models have advanced our understanding of brain shrinkage due to physiological and pathological aging, they often rely on simplified representations of tissue properties with limited regional differentiation. Building on established links between regional mechanics and neurodegeneration, we extend atrophy models by introducing detailed mechanical heterogeneity across 17 anatomically and mechanically distinct brain regions. Using region-specific experimental material properties, the model differentiates local mechanical behavior and reveals effects that homogeneous models overlook, providing new clinical insight into region-specific vulnerabilities. We then compare this heterogeneous model with progressively simplified variants to assess the impact of regional variability on brain deformation. While global and regional volume changes remain largely unaffected by mechanical heterogeneity, volume fractions of the corpus callosum and ventricles are sensitive to regional differences in material parameters. Analysis of the displacement field shows that mechanical heterogeneity significantly influences local displacement patterns within brain regions. Stress and stretch analyses reveal discrepancies between simplified and heterogeneous models, particularly in the corpus callosum, the internal brain structures, and some cortical regions. These results emphasize the importance of incorporating regional mechanical heterogeneity to enhance the accuracy of brain simulations and underscore the need for more comprehensive experimental characterization of brain tissue properties.