Default mode network abnormalities in mesial temporal lobe epilepsy: A study combining fMRI and DTI

Abstract

Studies of in mesial temporal lobe epilepsy (mTLE) patients with hippocampal sclerosis (HS) have reported reductions in both functional and structural connectivity between hippocampal structures and adjacent brain regions. However, little is known about the connectivity among the default mode network (DMN) in mTLE. Here, we hypothesized that both functional and structural connectivity within the DMN were disturbed in mTLE. To test this hypothesis, functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) were applied to examine the DMN connectivity of 20 mTLE patients, and 20 gender- and age-matched healthy controls. Combining these two techniques, we explored the changes in functional (temporal correlation coefficient derived from fMRI) and structural (path length and connection density derived from DTI tractography) connectivity of the DMN. Compared to the controls, we found that both functional and structural connectivity were significantly decreased between the posterior cingulate cortex (PCC)/precuneus (PCUN) and bilateral mesial temporal lobes (mTLs) in patients. No significant between-group difference was found between the PCC/PCUN and medial prefrontal cortex (mPFC). In addition, functional connectivity was found to be correlated with structural connectivity in two pairwise regions, namely between the PCC/PCUN and bilateral mTLs, respectively. Our results suggest that the decreased functional connectivity within the DMN in mTLE may be a consequence of the decreased connection density underpinning the degeneration of structural connectivity.

A Review of the Functional and Anatomical Default Mode Network in Schizophrenia

“…Of note, fiber tracts in the DMN, such as those connecting pCC to bilateral mTLs [20], and pCC to mPFC [21,22], are also detectable between homologous regions in nonhuman primates using effective tracers, suggesting the effectiveness of in vivo DTI tractography in tracing tracts. Subsequent neuroimaging studies [19] combining DTI tractography and fc-fMRI have confirmed a relationship between functional and anatomical connections within the DMN in agreement with Greicius et al [8], further implying that regions that are connected directly by fiber tracts also have significant functional connections, but the inverse condition need not be true because functional connections might be linked indirectly via multisynaptic connections or more distant cortical regions.…”

“…In a resting-state fcfMRI study, Greicius and colleagues [8] found that pCC shows significant functional connectivity with mPFC, inferior parietal cortex, parahippocampal gyrus, and inferior temporal cortex within the DMN in healthy volunteers, and these connections are minimally disrupted during task performance, indicating preservation of DMN functional connectivity across the rest and task conditions. Functional connectivity between pCC/PCUN and mPFC, and pCC/PCUN and mesial temporal cortex within the DMN was detected in both healthy controls and patients with mesial temporal lobe epilepsy, demonstrating the robustness of these relationships in health and disease [19].…”

Large‐scale brain networks are distinctly affected in right and left mesial temporal lobe epilepsy

“…Other studies have used different approaches (i.e., ICA, seed‐based connectivity) to explore some specific RSNs such as the DMN [Liao et al, 2011], perceptual [Zhang et al, 2009a], and attention networks [Zhang et al, 2009b]. These studies revealed altered networks, compared to controls.…”

“…These studies revealed altered networks, compared to controls. The overall activation of DMN in MTLE is apparently reduced, as well as the functional connectivity between its nodes [Liao et al, 2011]. Some of these studies also demonstrated that MTLE affects the attention networks and perceptual networks, resulting in significant abnormal impairment between their regions [Cataldi, et al, 2013].…”

Diffusion magnetic resonance imaging for Brainnetome: A critical review

“…Using DTI and fMRI, Teipel et al [100] and Greicius et al [101] showed that functional connectivity across the entire DMN is based on a distinct pattern of anatomical connectivity within the cerebral white matter. In addition, some psychiatric diseases, such as schizophrenia [102] , AD [103][104][105] , and epilepsy [106] , also demonstrate a decreased WMM connectivity within the DMN. In a recent review [4] , Hulvershorn et al used a dMRI-derived network to systematically review the dysfunctional connectivity in pediatric MDD.…”