Though some authors study rs-fcMRI networks from the graph theoretic perspective, the word “network” has been applied in a number of other contexts in the neuroimaging literature. Sets of regions that activate or deactivate at the same time have been called “networks”, as have regions whose functional timecourses show some statistical dependency (e.g., Bitan et al. 2007; Saur et al. 2010). Groups of voxels that have correlated timecourses or shared covariance in the rs-fcMRI signal (methods detailed below) are also often referred to as networks. However, none of these examples are well-defined networks in a broader sense (i.e., nodes related by edges). From this point forward in the present review, when describing data, we will use the word “network” to denote well-defined networks and will avoid this terminology when describing non-graph-theoretic “networks”.
