The default mode network (DMN) is a set of brain regions active during rest and self-referential thought. This review of studies up to August 2016 examined how DMN functional connectivity varies in healthy people by age, sex, cognitive function, and analysis method. DMN connectivity follows an inverse U-shape across the lifespan: strongest in adulthood, lowest in children and the elderly. Cognitive function positively correlates with DMN connectivity. Females show stronger intranetwork connectivity than males. Effects of analysis type were inconclusive. A voxel-wise meta-analysis for age confirmed an immature network in children versus adults and a stronger network in adults versus the elderly. Defining normal variation may help identify DMN changes in pathology.
The spatial layout of the brain's default mode network (DMN) fluctuates over time, even when a person is at rest. Using a sliding time window analysis of functional connectivity MRI data from 12 participants, the authors found that the spatial similarity of successive DMN maps varied at low frequencies and followed a 1/f power spectral pattern. A single voxel appeared within a group DMN map in at most 82% of time windows, indicating marked temporal variation. Incidental connectivity increased centrifugally toward brain areas outside the DMN core. The method, SliTICA, captures this spatial variance and may provide a more complete measure of a network's functional activity.