Altered functional connectivity and small-world in mesial temporal lobe epilepsy

Abstract

Background: The functional architecture of the human brain has been extensively described in terms of functional connectivity networks, detected from the low-frequency coherent neuronal fluctuations that can be observed in a resting state condition. Little is known, so far, about the changes in functional connectivity and in the topological properties of functional networks, associated with different brain diseases.

Methodology/principal findings: In this study, we investigated alterations related to mesial temporal lobe epilepsy (mTLE), using resting state functional magnetic resonance imaging on 18 mTLE patients and 27 healthy controls. Functional connectivity among 90 cortical and subcortical regions was measured by temporal correlation. The related values were analyzed to construct a set of undirected graphs. Compared to controls, mTLE patients showed significantly increased connectivity within the medial temporal lobes, but also significantly decreased connectivity within the frontal and parietal lobes, and between frontal and parietal lobes. Our findings demonstrated that a large number of areas in the default-mode network of mTLE patients showed a significantly decreased number of connections to other regions. Furthermore, we observed altered small-world properties in patients, along with smaller degree of connectivity, increased n-to-1 connectivity, smaller absolute clustering coefficients and shorter absolute path length.

Conclusions/significance: We suggest that the mTLE alterations observed in functional connectivity and topological properties may be used to define tentative disease markers.

Figure 1. Statistically significant differences in functional connectivity between patients and controls.

Nodes (individual ROIs) were differently colored according to the six anatomical subregions listed in Table 1 (see legend). Undirected edges were differently colored according to the significantly larger functional connectivity ( and , FDR corrected). The symbols denoted the positive and negative t value, respectively) in two-sample two-tailed t-test.

Figure 2. , and of a brain functional network.

(A) indicates the absolute clustering coefficient scaled to an equivalent parameters of a population of random graph, (B) indicates the shortest absolute path length scaled to an equivalent parameters of a population of random graph and (C) indicates the small-world-ness of network for the mTLE patients (blue circles) and healthy controls (red dots) as a function for different functional coefficient threshold (). (D) , (E) and (F) for mTLE patients (blue circles) and healthy controls (red dots) as a function of different degree of node thresholds (). Black star markers indicate statistically significant differences between two groups (two-sample two-tailed t-test, , FDR corrected). Vertical bars indicate estimated standard errors.

Figure 3. Relationship between the functional connectivity and epilepsy duration.

Significant negative correlation (, ) for the functional connectivity (correlation coefficient, ) between rIFGoper and lIFGtri with the epilepsy duration.