Multiscale cortical morphometry reveals pronounced regional and scale-dependent variations across the lifespan

Motivation: Characterising the changes in cortical morphology across the lifespan is fundamental for a range of research and clinical applications. Most studies to date have found a monotonic decrease in commonly used morphometrics, such as cortical thickness and volume, across the entire brain with increasing age. Any regional variations reported are subtle changes in the rate of decrease. However, these descriptions of morphological changes have been limited to a single length scale, or resolution. Here, we delineate the morphological changes associated with the healthy lifespan in multiscale morphometrics. Methods: Using MRI from subjects aged 6-88 years from NKI and CamCAN, we computed morphometrics at spatial scales ranging from 0.32 mm to 3 mm. We used generalised additive mixed models to account for site differences when extracting age trajectories. In a proof-of-principle application, we compared brain age estimations based on a single metric (pial surface area) computed at a single scale vs. multiple scales. Results: On the level of whole cortical hemispheres, lifespan trajectories show diverging and even opposing trends at different spatial scales, in contrast to the monotonic decreases of volume and thickness described so far. Pronounced regional differences between lobes also became apparent in scales over 0.7 mm. Using two complementary scales improved brain age estimates in RMSE by about 5 years. Conclusion: Our study provides a comprehensive multiscale description of lifespan effects on cortical morphology in an age range from 6-88 years. In future, this can be used as a normative model to compare individuals or cohorts, hence identifying morphological abnormalities. Our results reveal the complementary information contained in different spatial scales, suggesting that morphometrics should not be considered mere scalars, but functions of length scale.