Viewed from a perspective of temporal dynamics, the high similarity of node relationships within SSM and visual systems and the default mode system might indicate that these systems in particular are relatively stationary, whereas other subgraphs SB203580 research buy such as task control systems might have more dynamic sets of relationships. It should also be noted

that several studies (Buckner et al., 2009 and Cole et al., 2010) have implicated the default mode system as the seat of the most prominent “hubs” in rs-fcMRI brain graphs. Although default mode nodes may indeed have many ties, the isolated nature of the default mode subgraph recasts the meaning of these nodes as hubs in the context of brain-wide rs-fcMRI networks. One of the more striking features of the modified voxelwise analysis is that subgraphs appear to be

arranged in spatial motifs throughout the cortex. Figure 7 demonstrates the presence of motifs at a single threshold of the modified voxelwise analysis. For each subgraph, the distribution of its spatial interfaces (defined as en face voxels) with other subgraphs is plotted, and then these neighboring subgraphs are examined to see whether they are themselves unlikely to interface selleck screening library (implying a 3-step motif). For example, the light blue subgraph interfaces predominantly with red and yellow subgraphs, which are themselves miniscule portions

of each others’ borders (red is 3.5% of yellow’s border, and yellow is 2.6% of red’s border), implying a yellow-light blue-red motif. Plots of relevant subgraphs on brain surfaces visually confirm the presence of motifs. Three instances of this motif are demonstrated, for the light blue, black (salience), and green (dorsal attention) subgraphs. Other 3-step motifs are present but not shown (e.g., red-teal-purple), and these motifs can be found up and down subgraph hierarchies (i.e., thresholds). A principal concern about such spatial motifs is that they are artifactual—that they arise as intermediate mixtures of adjacent signals, particularly when averaging over subjects. C1GALT1 Although these concerns cannot be entirely excluded, several interposed subgraphs (e.g., the green dorsal attention system or the teal ventral attention system) have firm and extensive experimental bases. If these are not considered artifactual, then other subgraphs deserve similar consideration. At the onset of functional neuroimaging some 25 years ago, investigators made educated guesses about the types of operations that the human brain must perform, and designed experimental paradigms to elicit such operations (Lueck et al., 1989, Pardo et al., 1991, Petersen et al., 1988 and Posner et al., 1988).