The simplest index of influence is the node degree, and in many (but not all) cases the degree of a node will be highly correlated with other more complex influence measures. Many of these measures capture the “centrality” of network elements, for example expressed as the number of short communication paths that travel through each node or edge.28 This measure of “betweenness centrality” is related to communication processes, but is also often found to be highly correlated with

the related measure of “closeness,” quantifying the proximity of each node to the rest of the network. Another class of influence measures is based on the effect Inhibitors,research,lifescience,medical of node or edge deletion on short communication paths or network dynamics. For example, vulnerability measures the selleck products decrease (or, in some cases, the increase) in global efficiency due to the deletion of a single node or edge.29 The most central or influential nodes in a network are often referred to as “hubs,” but it should be noted that there is no unique way of detecting Inhibitors,research,lifescience,medical these hubs with graph theory tools. Instead, a conjunction of multiple influence

measures (eg, degree, betweenness, Inhibitors,research,lifescience,medical vulnerability) should be used when attempting to identify hub nodes.30 While measures of segregation, integration, and influence can express structural characteristics of a network from different perspectives, recent developments in characterizing network communities or modules can potentially unify these different perspectives into a more coherent account of how a given network can be decomposed into modules (segregation), Inhibitors,research,lifescience,medical how these modules are interconnected (integration), and which nodes or edges are important for linking modules together (influence). Community detection is an extremely active Inhibitors,research,lifescience,medical field in network

science.31 A number of new community detection techniques have found applications in the analysis of structural and functional brain networks. One of the most commonly- used community detection algorithms is based on Newman’s Q-metric32 coupled with an efficient optimization approach.33 Another approach called Infomap34 identifies communities on the basis of a model of a diffusive random walk, essentially utilizing the fact that a modular network restricts diffusion between communities. In contrast, the Q-metric essentially Carfilzomib captures the difference between the actually encountered within-module density of connections compared with what is expected based on a corresponding random model, given a particular partitioning of the network into modules. Since combinatorics makes it impractical to examine all possible module partitions, an optimization algorithm is needed to identify the single partition for which the Q-metric is maximized. quality control Several methodological issues have arisen in recent years that impact the way community detection is carried out in brain networks, particularly in networks describing functional connectivity (Figure 3).