Unrest at rest: default activity and spontaneous network correlations.

A series of recent empirical observations demonstrate structured activity patterns that exist during passive task states. One observation is that a network of regions, referred to as the default network, shows preferentially greater activity during passive task states as compared to a wide range of active tasks. The second observation is that distributed regions spontaneously increase and decrease their activity together within functional-anatomic networks, even under anesthesia. We believe these rest activity patterns may reflect neural functions that consolidate the past, stabilize brain ensembles, and prepare us for the future. Accumulating data further suggest that differences in rest activity may be relevant to understanding clinical conditions such as Alzheimer's disease and autism. Maps of spontaneous network correlations also provide tools for functional localization and study of comparative anatomy between primate species. For all of these reasons, we advocate the systematic exploration of rest activity.