FIGURE 3.

Global and local analysis of the REML ELBO. At the global level of a whole tissue type (grey or white matter), the gain in ELBO compared to OLS analyses is maximal with a single basis function in the REML estimation that contains the cubic power of the MDI values (α = 3, a). In grey matter regional analyses, the global optimal model (MDI³) was also the local optimal within most regions, primarily located in frontal areas (b). In posterior regions, the local optimal model involved the square power of the MDI. With the global optimal model, the local gain in ELBO showed a gradient in the anteroposterior direction, with the highest gain in frontal areas (c). This is consistent with typical motion of study participants during MRI examinations