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. 2013 May 14;80(20):1826-33.
doi: 10.1212/WNL.0b013e3182929f38. Epub 2013 Apr 17.

Traumatic Brain Injury Impairs Small-World Topology

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Free PMC article

Traumatic Brain Injury Impairs Small-World Topology

Anand S Pandit et al. Neurology. .
Free PMC article

Abstract

Objective: We test the hypothesis that brain networks associated with cognitive function shift away from a "small-world" organization following traumatic brain injury (TBI).

Methods: We investigated 20 TBI patients and 21 age-matched controls. Resting-state functional MRI was used to study functional connectivity. Graph theoretical analysis was then applied to partial correlation matrices derived from these data. The presence of white matter damage was quantified using diffusion tensor imaging.

Results: Patients showed characteristic cognitive impairments as well as evidence of damage to white matter tracts. Compared to controls, the graph analysis showed reduced overall connectivity, longer average path lengths, and reduced network efficiency. A particular impact of TBI is seen on a major network hub, the posterior cingulate cortex. Taken together, these results confirm that a network critical to cognitive function shows a shift away from small-world characteristics.

Conclusions: We provide evidence that key brain networks involved in supporting cognitive function become less small-world in their organization after TBI. This is likely to be the result of diffuse white matter damage, and may be an important factor in producing cognitive impairment after TBI.

Figures

Figure 1
Figure 1. High-level description of the processing steps required for graph theoretical analysis of resting-state fMRI
Reference nodes are defined from a group independent component analysis (A), and are used to extract time-series from resting-state functional MRI data (B). Group-wise partial correlation analysis is used to construct functional connectivity adjacency matrices (B), from which network metrics can be calculated (C).
Figure 2
Figure 2. Topographic connectivity maps in normal control and traumatic brain injury patient groups
Network connectivity in (A) normal controls and (B) traumatic brain injury patients. Node outline color indicates individual networks: Red = default mode network, blue = executive network, green = hippocampi. Each link represents a significant positive functional connection between node pairs. The area of each node is directly proportional to the normalized betweenness centrality of that node. The nodes are presented to maximize visualization and are not in exact anatomical location. 1 = Left parietal cortex, 2 = right parietal cortex, 3 = precuneus, 4 = anterior prefrontal cortex, 5 = anterior prefrontal cortex (superior frontal gyrus), 6 = posterior prefrontal cortex, 7 = left inferior frontal gyrus, 8 = right inferior frontal gyrus, 9 = right inferior parietal, 10 = left inferior parietal, 11 = left superior temporal sulcus, 12 = right superior temporal sulcus, 13 = posterior cingulate cortex, 14 = left hippocampal formation, 15 = right hippocampal formation. Node outline color indicates individual networks: red = default mode network, blue = executive network, green = hippocampi.
Figure 3
Figure 3. Comparison of local network characteristics between normal control and traumatic brain injury patient groups
Local node features compare (A) degree centrality, k, and (B) betweenness centrality, b, between normal controls and traumatic brain injury (TBI) patients. *Significant difference between controls and patients (p < 0.05). aPFC = anterior prefrontal cortex; aPFC-sfg = superior frontal gyrus of the anterior prefrontal cortex; lHF = left hippocampal formation; lIFG = left inferior frontal gyrus; lIP = left inferoparietal; lPC = left parietal cortex; lSTS = left superior temporal sulcus; pC = precuneus; pCC = posterior cingulate; pPFC = posterior prefrontal cortex; rHF = right hippocampal formation; rIFG = right inferior frontal gyrus; rIP = right inferoparietal; rPC = right parietal cortex; rSTS = right superior temporal sulcus.

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