Fig. 3.

Diffusion models leveraging multi-shell data show variable associations with age in white matter. A. Change in R² after the addition of linear, quadratic, and cubic age terms for each diffusion metric. Models included head motion and sex as linear covariates. B. Relationships between mean white matter values and age, after controlling for sex and data quality. GAMs were leveraged to more precisely estimate linear and non-linear effects as one spline. The derivative of these splines, representing the estimated rate of change, are depicted below the x-axis. Shaded area indicates where the confidence interval of the slope does not include 0.