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Epilepsy Res. 2016 Jul;123:20-8. doi: 10.1016/j.eplepsyres.2016.04.001. Epub 2016 Apr 5.

Low functional robustness in mesial temporal lobe epilepsy.

Author information

  • 1Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Ave., Rm 1005, Madison, WI 53705-2275, United States. Electronic address: garciaramos@wisc.edu.
  • 2Biomedical Engineering, University of Wisconsin, College of Engineering, 1415 Engineering Drive, Madison, WI 53706, United States. Electronic address: jie.z.song@gmail.com.
  • 3Department of Neurology, University of Wisconsin School of Medicine and Public Health, Matthews Neuropsychology Lab, 7223 UW Medical Foundation Centennial Building, 1685 Highland Ave., Madison, WI 53705-2281, United States. Electronic address: hermann@neurology.wisc.edu.
  • 4Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Ave., Rm 1005, Madison, WI 53705-2275, United States; Department of Neurology, University of Wisconsin School of Medicine and Public Health, Matthews Neuropsychology Lab, 7223 UW Medical Foundation Centennial Building, 1685 Highland Ave., Madison, WI 53705-2281, United States; Department of Radiology, University of Wisconsin School of Medicine and Public Health, E3/366 Clinical Science Center, 600 Highland Ave., Madison, WI 53792-3252, United States. Electronic address: vprabhakaran@uwhealth.org.

Abstract

OBJECTIVES:

Brain functional topology was investigated in patients with mesial temporal lobe epilepsy (mTLE) by means of graph theory measures in two differentially defined graphs. Measures of segregation, integration, and centrality were compared between subjects with mTLE and healthy controls (HC).

METHODS:

Eleven subjects with mTLE (age 36.5±10.9years) and 15 age-matched HC (age 36.8±14.0years) participated in this study. Both anatomically and functionally defined adjacency matrices were used to investigate the measures. Binary undirected graphs were constructed to study network segregation by calculating global clustering and modularity, and network integration by calculating local and global efficiency. Node degree and participation coefficient were also computed in order to investigate network hubs and their classification into provincial or connector hubs. Measures were investigated in a range of low to medium graph density.

RESULTS:

The group of patients presented lower global segregation than HC while showing higher global but lower local integration. They also failed to engage regions that comprise the default-mode network (DMN) as hubs such as bilateral medial frontal regions, PCC/precuneus complex, and right inferior parietal lobule, which were present in controls. Furthermore, the cerebellum in subjects with mTLE seemed to be playing a major role in the integration of their functional networks, which was evident through the engagement of cerebellar regions as connector hubs.

CONCLUSIONS:

Functional networks in subjects with mTLE presented both global and local abnormalities compared to healthy subjects. Specifically, there was significant separation between groups, with lower global segregation and slightly higher global integration observed in patients. This could be indicative of a network that is working as a whole instead of in segregated or specialized communities, which could translate into a less robust network and more prone to disruption in the group with epilepsy. Furthermore, functional irregularities were also observed in the group of patients in terms of the engagement of cerebellar regions as hubs while failing to engage DMN-related areas as major hubs in the network. The use of two differentially defined graphs synergistically contributed to findings.

KEYWORDS:

Functional hubs; Graph theory analysis; Mesial temporal lobe epilepsy; Resting-state fMRI

PMID:
27082649
PMCID:
PMC4867275
[Available on 2017-07-01]
DOI:
10.1016/j.eplepsyres.2016.04.001
[PubMed - in process]
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