The network topologies were characterized using measures of node degree, network density, and betweenness centrality on binary, undirected networks53. Each measure was calculated from the Brain Connectivity Matlab toolbox (http://www.brain-connectivity-toolbox.net) or custom written Matlab code (Mathworks, Natick, MA). In the present study, a node, n, is defined as an ROI within the brain that has a defined anatomical location and volume within standard brain space, and N is the set of all nodes. An edge is defined as a significant functional connection between two nodes, where aij is the connection status between node i and node j (i,j ∈ N). aij = 1 when there is a significant connection, and aij = 0 when no connection is present. Node degree quantifies the total number of edges connected to a particular node: . The density or total percent connectivity is the fraction of total number of edges in the network to the total number of possible edges: . Finally, betweenness centrality is the sum of all the shortest paths that pass through the node of interest weighted by the inverse of
