The strength of each node is defined as its average connectivity with all

other nodes, and the graph’s size is defined by the number of nodes in the largest connected component; a larger graph size indicates fewer disconnected nodes.66,67 Accumulating evidence suggests that the small-world topological properties of brain functional networks are altered in patients with schizophrenia. In one study, in 31 patients with schizophrenia compared with 31 healthy controls, functional connectivity between 90 cortical and subcortical regions was AZD2014 research buy estimated by partial correlation Inhibitors,research,lifescience,medical analysis and thresholded to construct a set of unidirected graphs.68 The healthy subjects demonstrated efficient small-world properties, whereas topological parameters of brain networks — strength and degree of connectivity — were decreased in patients with schizophrenia, especially in the prefrontal, parietal, and temporal lobes, consistent with a hypothesis of dysfunctional integration. In another study, in a sample of 203 patients with schizophrenia, Inhibitors,research,lifescience,medical compared with 259 healthy controls, multimodal network organization was noted to be abnormal, as measured by topological and

distance metrics of anatomical network organization, abstracted from Inhibitors,research,lifescience,medical fMRI data.69 Patients with schizophrenia, compared with controls, demonstrated reduced hierarchy throughout the small-world regime, and increased connection distance in the multimodal cortical network. The loss of frontal hubs and the emergence of nonfrontal Inhibitors,research,lifescience,medical hubs was also noted,

supporting the hypothesis of schizophrenia as a dysconnectivity syndrome, impacting the efficiency of a frontally dominated hierarchical network of multimodal cortical connections. Inhibitors,research,lifescience,medical Though the impact of genetic variation on network topology based on graph analyses has not yet been reported, moderate levels of heritability have been found for brain graph topology measured in a twin study using EEG, suggesting that genetic variation may Impact small-world organization and brain graph metrics.70 The next wave of imaging genetics: polygenic risk Just as imaging genetics will continue to incorporate increasingly sophisticated analytic methodologies, so too will imaging genetics evolve to incorporate increasingly sophisticated models of genetic risk, 4��8C reflective of the increasingly apparent polygenic complexity of psychiatric syndromes. Genome-wide association studies (GWAS) have indicated a highly significant polygenic component of schizophrenia risk, possibly involving up to thousands of common alleles of very small effect, at the population level.71 While early imaging genetics used intermediate phenotypes to assess the impact of single gene variants, recent studies have increasingly tended towards epistatic models of gene interaction.