Fast oscillations associated with interictal spikes localize the epileptogenic zone in patients with partial epilepsy

Abstract

Although interictal epileptic spikes are defined as fast transient activity, the spatial distribution of spike-related high-frequency power changes is unknown. In this study, we localized the sources of spike-locked power increases in the beta and gamma band with magnetoencephalography and an adaptive spatial filtering technique, and tested the usefulness of these reconstructions for determining the epileptogenic zone in a population of 27 consecutive presurgical patients with medication refractory partial epilepsies. The reliability of this approach was compared to the performance of conventional MEG techniques such as equivalent current dipole (ECD) models. In patients with good surgical outcome after a mean follow up time of 16 months (Engel class I or II), the surgically resected area was identified with an accuracy of 85% by sources of spike-locked beta/gamma activity, which compared favourably with the accuracy of 69% found for ECD models of single spikes. In patients with a total of more than 50 spikes in their recordings, the accuracies increased to 100% vs. 88%, respectively. Imaging of spike-locked beta/gamma power changes therefore seems to be a reliable and fast alternative to conventional MEG techniques for localizing epileptogenic tissue, in particular if more than 50 interictal spikes can be recorded.

Localization of cortico-peripheral coherence with electroencephalography

“…The MVBF uses the temporal covariance of the EEG data (in addition to the sensor geometry) to create a custom spatial filter depending on the signal characteristics. This en-ables more precise and focal source localizations (Sekihara et al, 2005;Dalal et al, 2008;Guggisberg et al, 2008b) that we also observe here in the simulations. However, beamformers are especially sensitive to the accuracy of the head model; measured data that is inconsistent with the head model is liable to be rejected as noise (Steinsträter et al, 2010).…”

Source localization using event related beamformer of magnetoencephalography for interictal spikes in pediatric neocortical epilepsy

“…This would have implications in the pre surgical evaluation by providing data ahead of surgery about brain regions that should be resected in order to achieve good surgical outcome thus assisting planning of the surgical procedure and allowing appropriate counseling of patients. Our data shows similar results to the results published by other authors using an adaptive spatial filtering method for localization of the sources of spike-locked beta and gamma activity in adults with intractable epilepsy [21].…”

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

“…Thus, recent studies suggest that epileptic oscillations can be detected in the beta/gamma band (Guggisberg et al 2008;Rampp et al 2010) as in our study, and even in the fast ripple band (Xiang et al 2009). As high frequency activity (HFOs [ 80 Hz) has been shown to be a good indicator of the seizure onset zone on intracerebral EEG (Worrell et al 2008;Bagshaw et al 2009;Zijlmans et al 2011), a promising venue would be to combine network localization on beta/low gamma oscillations with localization of HFOs (Van Klink et al 2014).…”