The fibres/tracts/connections shown in the beautiful pictures in the link below are often affected in older people by damage to microscopic arteries (arterioles) in the brain. This can contribute to depression and to neurocognitive problems, including dementia. (page 275 and pages 455-458 in my book). The ABC Science article provides a nice account of the way these pictures are produced, indirectly, via mathematical analysis from MRI imaging. Knowing about these connections can help us to understand how brain systems (rather than simply regions) work. This is mostly used as a research tool at present.
https://www.abc.net.au/news/science/2019-08-12/brainbows-brain-image-tractography-neuroscience/11363764