A key technical question in studying brain networks is the way in which connectivity is defined and measured. Structural connectivity, the stable direct physical pathways linking spatially distinct brain regions, is distinguished from the dynamical or state-dependent functional connectivity and effective connectivity. Effective connectivity describes the directional flow of information, or more generally, the causal relationships between nodes in a graph, e.g. relationships such as “changes in the activity of A lead to changes in the activity of B”. However, the techniques for determining effective connectivity are complex, and the tools available to analyze the resulting networks are limited. It is often significantly more straightforward, and much more common, to simply compute measures of statistical dependence (correlation) between nodes, which is dubbed functional connectivity.
