Increasing evidence is emerging that the functional and...
Increasing evidence is emerging that the functional and anatomical organization of the human brain follows a “small-world architecture” that involves a high degree of local clustering and selective long-range connections. This architecture allows both for segregated and distributed neural processing and enables an energy efficient processing mode in the cortex (Achard et al., 2006). Small-world properties are not confined to the human brain, however, but have been found in non-human primates and indeed in many other complex systems (see Bassett and Bullmore, 2006, for a review).
The current study by Bassett et al. (2008) provides important new evidence that the application of this approach may yield crucial insights into the pathophysiology of schizophrenia. In their study, Bassett and colleagues examined MRI data from 259 healthy volunteers and 203 scans from patients with schizophrenia. By analyzing the correlations of cortical thickness across subjects, the authors were able to examine the organizational structure of the anatomical network. Interestingly, the connectivity network in schizophrenia exhibited overall a small-world network topology similar to those found in controls. However, important differences emerged as well. The network architecture in patients with schizophrenia was characterized by an altered hierarchy of anatomical organization. Whereas in controls, the prefrontal cortex was a major hub that was connected to several cortical areas, this organization was absent in schizophrenia. Instead, patients with schizophrenia tended to show other hubs that were not present in controls, such as insula, thalamus, and temporal pole. In addition, the distance between nodes in a multimodal network was significantly decreased in schizophrenia, suggesting reduced connectivity in core structures of the cortex.
This approach by Bassett et al. underlines the utility of applying analysis techniques that examine the organization and structure of anatomical networks in schizophrenia. Schizophrenia is a disorder that likely involves not a single cortical area but affects large-scale anatomical connectivity. Future studies will be necessary to confirm this finding by extending the analysis of small-world properties to the analysis of high-resolution diffusion tensor imaging (DTI) data (see also the recent paper by Hagmann et al., 2008) as well as correlations between abnormal anatomical organization with functional brain imaging data in schizophrenia.
Achard S, Salvador R, Whitcher B, Suckling J, Bullmore E. (2006) A resilient, low-frequency, small-world human brain functional network with highly connected association cortical hubs. J Neuroscience 26(1):63-72. Abstract
Bassett DS, Bullmore E. (2006) Small-world brain networks. Neuroscientist 12(6):512-23. Review. Abstract
Hagmann P, Cammoun L, Gigandet X, Meuli R, Honey CJ, Wedeen VJ, Sporns O. (2008). Mapping the structural core of human cerebral cortex. PLoS Biol. 6(7):e159. Abstract