  The human brain is a complex network of interconnected brain regions
organized into functional modules with distinct roles in cognition and
behavior. An important question concerns the persistence and stability of these
modules over the human lifespan. Here we use graph-theoretic analysis to
algorithmically uncover the brain's intrinsic modular organization across
multiple spatial scales ranging from small communities comprised of only a few
brain regions to large communities made up of many regions. We find that at
coarse scales modules become progressively more segregated, while at finer
scales segregation decreases. Module composition also exhibits scale-specific
and age-dependent changes. At coarse scales, the module assignments of regions
normally associated with control, default mode, attention, and visual networks
are highly flexible. At fine scales the most flexible regions are associated
with the default mode network. Finally, we show that, with age, some regions in
the default mode network, specifically retrosplenial cortex, maintain a greater
proportion of functional connections to their own module, while regions
associated with somatomotor and saliency/ventral attention networks distribute
their links more evenly across modules.

Neurons and Cognition