Comparison of Brain Networks During Interictal Oscillations and Spikes on Magnetoencephalography and Intracerebral EEG

Abstract

Electromagnetic source localization in electroencephalography (EEG) and magnetoencephalography (MEG) allows finding the generators of transient interictal epileptiform discharges ('interictal spikes'). In intracerebral EEG (iEEG), oscillatory activity (above 30 Hz) has also been shown to be a marker of neuronal dysfunction. Still, the difference between networks involved in transient and oscillatory activities remains largely unknown. Our goal was thus to extract and compare the networks involved in interictal oscillations and spikes, and to compare the non-invasive results to those obtained directly within the brain. In five patients with both MEG and iEEG recordings, we computed correlation graphs across regions, for (1) interictal spikes and (2) epileptic oscillations around 30 Hz. We show that the corresponding networks can involve a widespread set of regions (average of 10 per patient), with only partial overlap (38 % of the total number of regions in MEG, 50 % in iEEG). The non-invasive results were concordant with intracerebral recordings (79 % for the spikes and 50 % for the oscillations). We compared our interictal results to iEEG ictal data. The regions labeled as seizure onset zone (SOZ) belonged to interictal networks in a large proportion of cases: 75 % (resp. 58 %) for spikes and 58 % (resp. 33 %) for oscillations in iEEG (resp. MEG). A subset of SOZ regions were detected by one type of discharges but not the other (25 % for spikes and 8 % for oscillations). Our study suggests that spike and oscillatory activities involve overlapping but distinct networks, and are complementary for presurgical mapping.

Integration of stationary wavelet transform on a dynamic partial reconfiguration for recognition of pre-ictal gamma oscillations

“…Importantly, these signals show a mixture of activities (transient waves and oscillations) which potentially imply different cortical regions. In a previous work, the difficulty of separation between these activities was emphasized and reliable filtering techniques was suggested, evaluated against several constraints [ 1 , 12 , 13 , 17 , 33 ]. Among these techniques, SWT was shown to be a convenient tool for the separation between transient and oscillations.…”

“…Thus, analyzing scalp electrophysiological signal (EEG, MEG) allows delineating the “epileptogenic zone” (EZ). The EZ is characterized by excessive excitability that may generate seizures; these discharges start from specific sources and propagate, involving large cortical areas forming networks [ 1 , 2 ]. During pre surgical evaluation, the decision can be made to implant invasive electrodes in order to define the pathological tissues that need to be removed by surgery.…”

Magnetoencephalography With Optically Pumped4He Magnetometers at Ambient Temperature

“…Its high temporal resolution in the order of the millisecond gives the possibility of an online observation of brain activity [1]. Within the main clinical applications, the use of MEG, in combination with stereoelectroencephalography (SEEG), led to a localization of 50 to 80 % of the epileptogenic sources [2]- [5] and has demonstrated its usefulness in epilepsy presurgical evaluation [6] [7]. MEG is also used in cognitive science to identify electrophysiological markers of brain activity in adults [8]- [10] and in children [11].…”

The interictal mesial temporal lobe epilepsy network

“…[22][23][24] The interictal spike region, also termed irritative zone, extends beyond the seizure onset zone but most often includes it. We therefore used interictal spikes, a reliable biomarker of epilepsy, whose temporal and spatial features correlate well with those of seizures.…”

“…We therefore used interictal spikes, a reliable biomarker of epilepsy, whose temporal and spatial features correlate well with those of seizures. [22][23][24] The interictal spike region, also termed irritative zone, extends beyond the seizure onset zone but most often includes it. 25 Perhaps, by an extension of Hebbian learning to the pathological state, regions that are coactivated during interictal spikes develop abnormally strong connections, resulting in an epileptogenic network.…”