Nodes in brain BMS-754807 concentration networks represent structurally and functionally homogeneous brain regions. Parcellation of whole-brain MRI scans into a collection of such nodes is an active and important area of research.42 Links in brain networks represent anatomical or functional interactions. In MRI datasets, anatomical links are defined using two main methods. The method of structural correlation is based on the principle that anatomically connected regions share common trophic factors and correlate in size. This method defines links as correlations in interregional gray-matter

volume or thickness inferred from a group of subjects, such that one network is constructed Inhibitors,research,lifescience,medical for the whole group.43 The method of diffusion-imaging tractography is based on the principle of anisotropic water diffusion along white-matter tracts and detects large-scale interregional anatomical links more directly such that one network is constructed for each subject.44 Functional links are defined as

correlations of interregional low-frequency fluctuations in blood-oxygen-level-dependent (BOLD) signal, an Inhibitors,research,lifescience,medical indirect measure of neural Inhibitors,research,lifescience,medical activity based on concentration of oxygenated hemoglobin in brain tissue45; with this method one network is likewise constructed for each subject. These different types of connectivity are complementary and each offers distinct insights into interactions between brain regions. The empirical study of brain networks has broadly and somewhat arbitrarily proceeded along two methodologically distinct lines of work. One line of work studies small networks of several brain regions46; the other line of work studies large networks of the whole brain.25 Investigators define small networks with methods such as seed

correlation analysis47 (the detection of structurally or functionally Inhibitors,research,lifescience,medical similar neighbors for an a priori defined “seed” region) and independent component analysis48 (the delineation of the brain Inhibitors,research,lifescience,medical into a set of maximally independent small networks), and with modeling approaches.49,50 Small networks are usually associated with specific functional tasks: a classic example is of the language network associated with the comprehension and production of language51; a prominent recent example is the default network associated with internallyfocused cognition.52 Associations with functional tasks make small networks comparatively easy to interpret and the study of such networks has a long tradition in neurology.53 Nonetheless small networks may provide limited Oxalosuccinic acid insight into characteristic abnormalities of schizophrenia if such abnormalities involve widespread disturbances of integration, as is likely to be the case. Calhoun et al54 review abnormalities of small functional brain networks in schizophrenia. In this article we focus on large networks involving many nodes and describing the complete structural or functional maps of interregional interactions of the brain, the human connectome (Figure 1a).