In brain structure, we used pattern extraction algorithms to identify statistically rigorous links between DMN gray matter (sMRI) and white matter tract properties (dMRI)—two types of brain imaging usually studied separately. Our multimodal approach determined whether volume differences of DMN subregions are informative about microstructural features of axonal fiber bundles. Among 48 examined anatomical tracts, fornix fibers had the strongest association with DMN gray matter patterns, explaining up to 24% of this tract’s population variability. As with other small fiber tracts analyzed by diffusion imaging with tract-based spatial statistics (26), it is challenging to completely exclude the possibility that mild partial volume effects have influenced our fornix−DMN association results. Cerebrospinal fluid contamination may be alleviated by more sophisticated voxel-by-voxel correction techniques (27). Nevertheless, our predictive association of DMN gray matter with fornix fiber bundles was robust in 10,000 individuals and appears to fill an important gap in the neuroscience literature.
