Trends in Cognitive Sciences
ReviewSpecial Issue: The Connectome – Feature ReviewNetwork hubs in the human brain
Section snippets
The central role of integrative processes and communication
Since the beginning of modern neuroscience, the brain has generally been viewed as an anatomically differentiated organ whose many parts and regions are associated with the expression of specific mental faculties, behavioral traits, or cognitive operations [1]. The idea that individual brain regions are functionally specialized and make specific contributions to mind and cognition is supported by a wealth of evidence from both anatomical and physiological studies as well as from noninvasive
Methodological aspects: detection and classification of hubs in brain networks
Brain networks can be mathematically described as graphs, essentially comprising sets of nodes (neuronal elements) and edges (their interconnections) whose pairwise couplings are summarized in the network's connection matrix and whose arrangement defines the network's topology (Figure 1). The extraction of brain networks from human imaging data as well as the many opportunities and limitations of graph-based approaches have been the subject of numerous recent reviews 20, 24, 25, 26, 27, 28. One
Structural hubs
Compiling macroscale connectome maps of the human brain from diffusion imaging data, several studies have noted the existence of a specific set of hub regions (Figure 2). Network analyses have consistently identified the precuneus, anterior and posterior cingulate cortex, insular cortex, superior frontal cortex, temporal cortex, and lateral parietal cortex as densely anatomically connected regions with a central position in the overall network 38, 54, 55, 56, 57, 58, 59, 60, 61, 62, using
Hubs and network communication
The status of candidate hub regions and their connections as influential network elements rests on their central embedding in the brain's network. This notion implies that neural hubs derive their influence from their strong participation in dynamic interactions due to neuronal signaling that is, from their central role in neuronal communication processes unfolding within the structural network. The concept of brain hubs is therefore closely linked to an assessment of network communication. An
Concluding remarks
Complex cognitive operations emerge from the coordinated activity of large neuronal populations in distributed brain networks. Network theory identifies several highly connected and highly central hub regions and predicts that these network hubs and their connections play key roles in the integration of information and in efficient neuronal signaling and communication in the brain. Network analysis tools applied to structural and functional human connectome data provide a data-driven
Acknowledgments
M.P.v.d.H. was supported by a VENI (#451-12-001) grant of the Netherlands Organization for Scientific Research (NWO). O.S. was supported by the J.S. McDonnell Foundation.
Glossary
- Brain connectivity
- description of structural or functional connectivity between brain network elements (i.e., brain regions, neurons).
- Centrality
- measures of the relative importance of a node or edge within the overall architecture of a network. Several centrality metrics have been proposed, including (among many others) degree, betweenness, closeness, eigenvector, and pagerank centrality.
- Clustering
- the tendency of small groups of nodes to form connected triangles. Many triangles around a central
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