Dense Array EEG Source Estimation in Neocortical Epilepsy

Abstract

Rationale: Dense array EEG (dEEG) evenly covers the whole head surface with over 100 channels contributing to more accurate electrical source imaging due to the higher spatial and temporal resolution. Several studies have shown the clinical utility of dEEG in presurgical clinical evaluation of epilepsy. However validation studies measuring the accuracy of dEEG source imaging are still needed. This can be achieved through simultaneously recording both scalp dEEG with intracranial electrodes (icEEG), which is considered as the true measure of cortical activity at the source. The purpose of this study is to evaluate the accuracy of 256-channel dEEG electrical source estimation for interictal spikes.Methods: Four patients with medically refractory neocortical epilepsy, all surgical candidates, underwent subdural electrode implantation to determine ictal onset and define functional areas. One patient showed a lesion on the magnetic resonance imaging in the right parietal lobe. The patient underwent simultaneous recording of interictal spikes by both scalp 256-channelsvdEEG and icEEG. The dEEG was used to non-invasively estimate the source of the interictal spikes detected by the 256-channel dEEG array, which was then compared to the activity measured directly at the source by the icEEG.Results: From the four patients, a total of 287 interictal spikes were measured with the icEEG. One hundred fifty-five of the 287 spikes (54%) were visually detected by the dEEG upon examination of the 256 channel head surface array. The spike amplitudes detected by the 256-channel dEEG correlated with icEEG spike amplitudes (p < 0.01). All spikes detected in dEEG were localized to the same lobe correctly.Conclusion: Our study demonstrates that 256-channel dEEG can reliably detect interictal spikes and localize them with reasonable accuracy. Two hundred fifty-six-channel dEEG may be clinically useful in the presurgical workup for epilepsy and also reduce the need for invasive EEG evaluation.

Analysis of infant cortical synchrony is constrained by the number of recording electrodes and the recording montage

“…It is well established that the accuracy of EEG study can be improved by increasing spatial sampling with higher number of EEG electrodes (Lantz et al, 2003;Yamazaki et al, 2013). In support of this, we observed no 'ceiling effect' with respect to the electrode count (Figs.…”

High density EEG—What do we have to lose?

“…Multiple studies have demonstrated the utility of electrical source imaging (ESI) of high density EEG recordings for improved localization of epileptic foci in surgical candidates compared to visual interpretation of the conventional scalp EEG (Lantz et al, 2003; Holmes et al, 2008, 2010; Yamazaki et al, 2013; Storti et al, 2013; Mégevand et al, 2014; Michel et al., 2004a,b; Brodbeck et al, 2010; Zumsteg et al, 2005; Lantz et al, 2001; Brodbeck et al, 2009). A large prospective study in 151 pediatric and adult epilepsy surgery patients found that ESI using 126–256 channels and individual brain MRIs as the head model yielded a sensitivity of 84% and a specificity of 88% in identifying the seizure onset zone, which was significantly better than that obtained using low-density EEG recordings, structural MRI, PET exam, or ictal SPECT exams (Brodbeck et al, 2011).…”

Identifying the Epileptic Network

“…In their chapter in this volume, Yamazaki et al (7) extend this work to cases of neocortical epilepsy by demonstrating that dEEG, by covering the whole head with sufficient sensor density, can reliably localize epileptiform discharges when compared to invasive studies.…”

“…Yamazaki et al (7) have pioneered the ability to simultaneously record 256 channel dense EEG (dEEG) and invasive subdural EEG recordings in temporal lobe epilepsy, thus helping to establish the validity of dEEG recordings. In their chapter in this volume, Yamazaki et al (7) extend this work to cases of neocortical epilepsy by demonstrating that dEEG, by covering the whole head with sufficient sensor density, can reliably localize epileptiform discharges when compared to invasive studies.…”