Edited by Marcus E. Raichle, Washington University in St. Louis, St. Louis, MO, and approved October 19, 2012 (received for review June 9, 2012)
Human brain networks have topological properties in common with many other complex systems, prompting the following question: what aspects of brain network organization are critical for distinctive functional properties of the brain, such as consciousness? To address this question, we used graph theoretical methods to explore brain network topology in resting state functional MRI data acquired from 17 patients with severely impaired consciousness and 20 healthy volunteers. We found that many global network properties were conserved in comatose patients. Specifically, there was no significant abnormality of global efficiency, clustering, small-worldness, modularity, or degree distribution in the patient group. However, in every patient, we found evidence for a radical reorganization of high degree or highly efficient “hub” nodes. Cortical regions that were hubs of healthy brain networks had typically become nonhubs of comatose brain networks and vice versa. These results indicate that global topological properties of complex brain networks may be homeostatically conserved under extremely different clinical conditions and that consciousness likely depends on the anatomical location of hub nodes in human brain networks.
Author contributions: S.A., C.D.-M., M.S., F.S., S.K., and E.T.B. designed research; S.A., M.S., S.K., and E.T.B. performed research; S.A., P.E.V., F.R., C.H., and E.T.B. contributed new reagents/analytic tools; S.A., C.D.-M., P.E.V., and E.T.B. analyzed data; M.S. in charge of patients and data acquisition; F.S. in charge of patients; S.K. performed data acquisition; and S.A., C.D.-M., P.E.V., F.S., S.K., and E.T.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1208933109/-/DCSupplemental.
