Study on the Relationships between Intrinsic Functional Connectivity of the Default Mode Network and Transient Epileptic Activity.

Renaud Lopes,Pierre Besson,Friederike Moeller,Michael Siniatchkin,Philippe Derambure,Mathilde Chipaux,Xavier Leclerc,William Szurhaj,Franã§Ois Ogez,Louise Tyvaert

doi:10.3389/fneur.2014.00201

Abstract

Rationale: Simultaneous recording of electroencephalogram and functional MRI (EEG–fMRI) is a powerful tool for localizing epileptic networks via the detection of hemodynamic changes correlated with interictal epileptic discharges (IEDs). fMRI can be used to study the long-lasting effect of epileptic activity by assessing stationary functional connectivity during the resting-state period [especially, the connectivity of the default mode network (DMN)]. Temporal lobe epilepsy (TLE) and idiopathic generalized epilepsy (IGE) are associated with low responsiveness and disruption of DMN activity. A dynamic functional connectivity approach might enable us to determine the effect of IEDs on DMN connectivity and to better understand the correlation between DMN connectivity changes and altered consciousness.Method: We studied dynamic changes in DMN intrinsic connectivity and their relation to IEDs. Six IGE patients (with generalized spike and slow-waves) and 6 TLE patients (with unilateral left temporal spikes) were included. Functional connectivity before, during, and after IEDs was estimated using a sliding window approach and compared with the baseline period.Results: No dependence on window size was observed. The baseline DMN connectivity was decreased in the left hemisphere (ipsilateral to the epileptic focus) in TLEs and was less strong but remained bilateral in IGEs. We observed an overall increase in DMN intrinsic connectivity prior to the onset of IEDs in both IGEs and TLEs. After IEDs in TLEs, we found that DMN connectivity increased before it returned to baseline values. Most of the DMN regions with increased connectivity before and after IEDs were lateralized to the left hemisphere in TLE (i.e., ipsilateral to the epileptic focus).Conclusion: Results suggest that DMN connectivity may facilitate IED generation and may be affected at the time of the IED. However, these results need to be confirmed in a larger independent cohort.

Highlights

Epilepsy is a common neurological disease defined by the occurrence of electrically and clinically measurable epileptic seizures.Abbreviations: BOLD, blood oxygen level dependent; DMN, default mode network; dMPFC, dorsal medial prefrontal cortex; EEG, electroencephalogram; fMRI, functional magnetic resonance imaging; HRF, hemodynamic response function; Independent component analysis (ICA), independent component analysis; interictal epileptic discharges (IEDs), interictal epileptic discharge; IGE, idiopathic generalized epilepsy; IPL, inferior parietal lobule; MFG, middle frontal gyrus; MTG, middle temporal gyrus; NBS, network-based statistics; PCC, precuneus/posterior cingulate cortex; PHG, parahippocampal gyrus; resting-state networks (RSNs), resting-state network; Temporal lobe epilepsy (TLE), temporal lobe epilepsy; TP, temporal pole; windows of interest (WOIs), window of interest.Cognitive and behavioral functions may be altered, leading to severe social and professional handicap
After IEDs in TLEs, we found that DMN connectivity increased before it returned to baseline values
Results suggest that DMN connectivity may facilitate IED generation and may be affected at the time of the IED

Summary

Introduction

Epilepsy is a common neurological disease defined by the occurrence of electrically and clinically measurable epileptic seizures. Cognitive and behavioral functions may be altered, leading to severe social and professional handicap. The patient’s clinical state is altered at the time of the ictal event and during the immediate postictal period. Functional brain impairments can be observed during the interictal state. These cognitive impairments may be due to factors such as structural lesions, medication effects, the underlying cause of epilepsy, and/or the occurrence of interictal epileptic discharges (IEDs) observed in electroencephalography (EEG). The repetition of IEDs may be responsible for long-lasting effects on the brain’s functional plasticity and may lead to cognitive disturbances [1].

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