Hubs perform important integrative roles in structural networks, but until fairly recently it has been unclear how they connect and interact with each other. Several early

studies carried out in humans and other species had suggested a tendency for hubs to be densely interconnected in a “hub complex,” 30 or a structural core (Figure 5).56 Network studies in other disciplines have pointed Inhibitors,research,lifescience,medical to the existence of a “rich club,” a set of hub regions that are more densely interconnected than predicted by chance alone.67 Rich clubs may be significant features of network architecture as they provide a structural substrate for integrating and selleck disseminating information across the entire network. The first report on rich club organization came from a study of cat cerebral cortex, where a rich club of hub regions was found to form a densely interconnected core circuit cross-linking all major functional subsystems.68 A detailed analysis Inhibitors,research,lifescience,medical of the topology of human brain structural connectivity acquired with diffusion imaging and tractography revealed a rich club of highly interconnected hub regions including portions of the superior frontal cortex, superior parietal cortex, and the precuneus, in addition to Inhibitors,research,lifescience,medical several subcortical regions including the thalamus, hippocampus, and part of the basal

ganglia.69 Graph analysis showed that 89% of all short communication paths among non-rich club regions across the network pass through the rich club, and that damage to pathways linking rich club regions to each other had a larger disruptive

effect on network communication than equal amount of damage to connections among non-rich club regions. Figure 5. Modules, cores, and rich clubs. (A) A schematic network composed of four modules that are linked Inhibitors,research,lifescience,medical by hub nodes (black). These hub nodes are clearly important for connecting modules to each other, but they are only weakly interconnected amongst each other. Inhibitors,research,lifescience,medical … Rich club organization has been confirmed and extended in subsequent studies focusing on the role of the rich club in brain communication,70 its disruption in a mental disorder,71 and its presence in the cerebral cortex of a non-human primate, the macaque monkey.72 The latter study not only demonstrated rich club organization in a directed network of inter-regional projections derived from classical most tract tracing studies, but also showed again that the rich club is interspersed between structural and functional communities. The macaque rich club contains several regions of association cortex that are homologues to rich club regions found in the human brain. The emerging picture of the organization of the human connectome is one of a modular small world network, with network communities that are interlinked by a coherent sub-network or core of hub regions whose position within the overall network is strongly suggestive of a central role in global information flow and integration.