This modification arose from several practical observations. First, nearby voxels share nonbiological signal (causing increased rs-fcMRI correlation), a result of unavoidable steps in data processing (e.g., reslicing, blurring). Second, short-distance relationships are especially susceptible to spurious augmentation by subject motion (Power et al., 2011). Third, as will be seen shortly, voxelwise graphs are dominated at higher thresholds by short-distance relationships, which are logically partially artificial based

on the above considerations. buy MK0683 Modified voxelwise networks are presented in which all ties terminating within 20 mm of a source node are excluded, though other distances (e.g., 15 mm and 25 mm) were also tested, with similar results (data not shown). The two standard methods of graph formation were parcel-based and voxel-based. The parcel-based graph was formed Selleck PD-L1 inhibitor using the 90-parcel AAL atlas (Tzourio-Mazoyer et al., 2002), a popular method of graph formation. This atlas divides the cortex and subcortical structures into parcels based upon anatomical landmarks. The voxel-based graph was defined using all voxels within the AAL atlas (n = 40,100), and the modified voxelwise graph was also defined using these voxels. Subgraphs were determined over a range of thresholds for each graph using one of the best-performing subgraph detection algorithms currently available

(Infomap) (Fortunato, 2010 and Rosvall and Bergstrom, 2008). This algorithm uses the map equation to minimize information theoretic descriptions Resminostat of random walks on

the graph (essentially assigning zip codes to subgraphs to shorten addresses of individual nodes). Other algorithms were tested and yielded similar results (Figure S2). Figure 1 illustrates our methodology and highlights several important results. The first panel depicts the areal graph in a spring embedded layout and maps subgraphs onto nodes using colors, visibly demonstrating the basis for subgraphs. In spring embedded layouts, ties act as springs to position nodes in space such that well-connected groups of nodes are pulled together, providing an intuitive and informative picture of the graph. The second panel shows the subgraph assignments of the areal network in both cohorts over a range of thresholds (each chart consists of 9 columns of 264 color entries). ROIs are ordered identically for both cohorts, and the patterns of subgraph assignment across cohorts are in good agreement. The standard graph theoretic measure of similarity between two sets of node assignments is normalized mutual information (NMI), which measures how much information one set of assignments provides about another set of assignments. Values of 1 indicate identical assignments, and values of 0 indicate that no information is gained about the second set of assignments by knowing the first. Between cohorts, NMI ranges from 0.86 to 0.