High resolution diffusion tensor imaging shows non-linear trajectories in the human cortex over the healthy lifespan

The brain cortex is thin and has a complex morphology making it difficult to analyze with in vivo diffusion MRI. A high-resolution 1.5 mm isotropic diffusion MRI protocol and an automated cortex segmentation methodology on the diffusion images alone was used to assess cortical diffusion changes over the healthy lifespan (n=165, 5-74 years). The diffusion metrics versus age trajectories differed across the cortical surface despite similar cortical thickness reductions with age. The most robust age changes were for axial diffusivity (quadratic U) and radiality (cubic) potentially reflecting changes in columnar microstructural organization of the cortex in typical development and aging.