Distinct functional and structural <scp>MRI</scp> abnormalities in mesial temporal lobe epilepsy with and without hippocampal sclerosis

Coan, Ana Carolina; Campos, Brunno M.; Beltramini, Guilherme C.; Yasuda, Clarissa L.; Covolan, R. J. M.; Cendes, Fernando

doi:10.1111/epi.12670

Cited by 35 publications

(31 citation statements)

References 39 publications

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“…Furthermore, contrary to the mTLE group, the healthy subjects engaged the right PCC and precuneus along with bilateral medial frontal gyrus, and bilateral inferior parietal lobule (IPL) as connector hubs, which are important areas from the DMN (Buckner et al, 2009; Mevel et al, 2013; Persson et al, 2007). In this study, subjects with mTLE were not engaging the majority of the expected regions as main hubs, especially the PCC and precuneus, which coincides with previous publications that found disrupted DMN in mTLE patients (Coan et al, 2014; Liao et al, 2010; McCormick et al, 2013). Along with the lack of recruitment of most DMN-related regions as hubs, mTLE participants presented four regions from the cerebellum as connector hubs in the network while controls only presented two cerebellar regions only as provincial hubs.…”

Section: Discussionsupporting

confidence: 92%

Low functional robustness in mesial temporal lobe epilepsy

Garcia‐Ramos

Song²,

Hermann

et al. 2016

Epilepsy Research

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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 ± 10.9 years) and 15 age-matched HC (age 36.8 ± 14.0 years) 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.

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Section: Discussionsupporting

confidence: 92%

Low functional robustness in mesial temporal lobe epilepsy

Garcia‐Ramos

Song²,

Hermann

et al. 2016

Epilepsy Research

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“…One possible factor involved on RSN disruption in MTLE patients may be the underlying interictal activity. Although we do not have concomitant EEG recordings to this data, previous studies described the functional alterations caused by interictal spikes [Coan et al, 2014a]. However, there is no evidence that the characteristics of interictal epileptiform discharges, including rate, localization or extent, differ between right or left MTLE and, accordingly, these differences were also not observed between our groups of patients.…”

Section: Differences Of Abnormal Connectivity Between Right and Left mentioning

confidence: 62%

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

Campos

Coan

Yasuda

et al. 2016

Human Brain Mapping

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108

102

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Mesial temporal lobe epilepsy (MTLE) with hippocampus sclerosis (HS) is associated with functional and structural alterations extending beyond the temporal regions and abnormal pattern of brain resting state networks (RSNs) connectivity. We hypothesized that the interaction of large‐scale RSNs is differently affected in patients with right‐ and left‐MTLE with HS compared to controls. We aimed to determine and characterize these alterations through the analysis of 12 RSNs, functionally parceled in 70 regions of interest (ROIs), from resting‐state functional‐MRIs of 99 subjects (52 controls, 26 right‐ and 21 left‐MTLE patients with HS). Image preprocessing and statistical analysis were performed using UF2C‐toolbox, which provided ROI‐wise results for intranetwork and internetwork connectivity. Intranetwork abnormalities were observed in the dorsal default mode network (DMN) in both groups of patients and in the posterior salience network in right‐MTLE. Both groups showed abnormal correlation between the dorsal‐DMN and the posterior salience, as well as between the dorsal‐DMN and the executive‐control network. Patients with left‐MTLE also showed reduced correlation between the dorsal‐DMN and visuospatial network and increased correlation between bilateral thalamus and the posterior salience network. The ipsilateral hippocampus stood out as a central area of abnormalities. Alterations on left‐MTLE expressed a low cluster coefficient, whereas the altered connections on right‐MTLE showed low cluster coefficient in the DMN but high in the posterior salience regions. Both right‐ and left‐MTLE patients with HS have widespread abnormal interactions of large‐scale brain networks; however, all parameters evaluated indicate that left‐MTLE has a more intricate bihemispheric dysfunction compared to right‐MTLE. Hum Brain Mapp 37:3137–3152, 2016. © 2016 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

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“…45 These differences would increase variability in the presented work. However, fMRI activation resulting from interictal spikes have been detected in the ipsilateral anterior temporal lobe and insula in both patients with and without hippocampal sclerosis, 46 and thalamic volume loss was also measured in both types of patients. 47 This suggests that our choice of an ipsilateral epileptogenic network including the hippocampus, insula, and thalamus is appropriate for all patients in this study.…”

Section: Discussionmentioning

confidence: 99%

Segmentation of the thalamus based on BOLD frequencies affected in temporal lobe epilepsy

2015

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Objective Temporal lobe epilepsy is associated with functional changes throughout the brain, particularly including a putative seizure propagation network involving the hippocampus, insula and thalamus. We identified a specified frequency range where functional connectivity in this network was related to duration of disease. Then, to identify specific thalamic nuclei involved in seizure propagation, we determined the subregions of the thalamus that have increased resting functional oscillations in this frequency range. Methods Resting-state functional MRI (fMRI) was acquired from twenty unilateral TLE (14 right, 6 left) patients and twenty healthy controls who were each age and gender matched to a specific patient. Wavelet based functional MRI connectivity mapping across the network was computed at each frequency to determine those frequencies where connectivity significantly decreases with duration of disease consistent with impairment due to repeated seizures. The voxel-wise power of the spontaneous blood oxygenation fluctuations of this frequency band was computed in the thalamus of each subject. Results Functional connectivity was impaired in the proposed seizure propagation network over a specific range (0.0067–0.013 Hz and 0.024–0.032 Hz) of blood oxygenation oscillations. Increased power in this frequency band (<0.032 Hz) was detected bilaterally in the pulvinar and anterior nucleus of the thalamus of healthy controls, and was increased over the ipsilateral thalamus compared to the contralateral thalamus in TLE. Significance This study identified frequencies of impaired connectivity in a TLE seizure propagation network and used them to localize the anterior nucleus and pulvinar of the thalamus as subregions most susceptible to TLE seizures. Further examinations of these frequencies in healthy and TLE subjects may provide unique information relating to the mechanism of seizure propagation and potential treatment using electrical stimulation.

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Distinct functional and structural MRI abnormalities in mesial temporal lobe epilepsy with and without hippocampal sclerosis

Cited by 35 publications

References 39 publications

Low functional robustness in mesial temporal lobe epilepsy

Low functional robustness in mesial temporal lobe epilepsy

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

Segmentation of the thalamus based on BOLD frequencies affected in temporal lobe epilepsy

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