Spectral bandwidth of fast epileptic activity within the epileptic focus is more narrow-banded within compared to outside the epileptic focus. To measure spectral bandwidth the relative power during fast epileptic activity is plotted against its spectral frequency. For this study the width at half of the maximum (FWHM) of the spectral peak was used.
Fast oscillatory EEG patterns between epileptic seizures are known to help identifying the origin of focal seizures. This area, where the seizures arise from, needs to be defined for surgical treatment of focal epilepsy. Up to now it was unclear, which are the key parameters to correlate fast oscillations with the area of seizure onset. In their recent article scientists from the Epilepsy Center Freiburg and their collaborators report that narrow-banded spectral changes of fast epileptic activity closely relate to the area of seizure onset (see figure above). This was true for fast epileptic activity in a broad range of frequencies between 14-250 Hz. The observed spectral changes may reflect dampened oscillations as effect of the complex interplay between excitation and inhibition of neural populations. In this view, reduced dampening of fast epileptic activity in focal epilepsy manifests in fast oscillations of narrow spectral bandwidth inside compared to broad spectral bandwidth outside the seizure onset zone.
An interesting additional result is that, Heers et al. identified interictal fast epileptic patterns only in intracranial EEG recordings of epilepsy patients with malformations of the cortical development named focal cortical dysplasia. Thus, these patterns are supposed to be specific for this type of brain lesion as it was reported before.
For future projects spectral bandwidth changes of fast epileptic activity can be a parameter to determine the added value of subdural high-resolution grid electrodes that are developed. They may also prove useful as target parameter for closed-loop intervention systems in epilepsy patients.
Original publication:
Heers M, Helias M, Hedrich T, Dümpelmann M, Schulze-Bonhage A, Ball T Spectral bandwidth of interictal fast epileptic activity characterizes the seizure onset zone. 2018 Neuroimage Clin, volume: 17, page(s): 865 - 872