Review
Special Issue: The Connectome – Feature Review
Network hubs in the human brain

https://doi.org/10.1016/j.tics.2013.09.012Get rights and content

Highlights

  • Brain hubs can be detected with tools and methods of graph theory.

  • Network studies have consistently identified structural hubs in cerebral cortex.

  • Hubs are central in brain communication and neural integration.

  • Hubs participate widely across a diverse set of cognitive functions.

  • High centrality makes hubs susceptible to disconnection and dysfunction.

Virtually all domains of cognitive function require the integration of distributed neural activity. Network analysis of human brain connectivity has consistently identified sets of regions that are critically important for enabling efficient neuronal signaling and communication. The central embedding of these candidate ‘brain hubs’ in anatomical networks supports their diverse functional roles across a broad range of cognitive tasks and widespread dynamic coupling within and across functional networks. The high level of centrality of brain hubs also renders them points of vulnerability that are susceptible to disconnection and dysfunction in brain disorders. Combining data from numerous empirical and computational studies, network approaches strongly suggest that brain hubs play important roles in information integration underpinning numerous aspects of complex cognitive function.

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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