Using ictal high-frequency oscillations (80-500Â Hz) to localize seizure onset zones in childhood absence epilepsy: A MEG study

This study aimed to use ictal high-frequency oscillations (HFOs) ranging from 80 Hz to 500 Hz to locate seizure onset zones in childhood absence epilepsy (CAE) using non-invasive magnetoencephalography (MEG). Ten drug-naïve children with CAE were studied using a 275-channel MEG system. MEG data were digitized at a sampling rate of 6000 Hz. HFO spectral power in real-time spectrograms was assessed using Morlet continuous wavelet transform. Magnetic sources were volumetrically localized through dynamic magnetic source imaging with a slide window. HFOs were identified in all patients. The total time of fast ripples (250-500 Hz) was greater than that of ripples (80-250 Hz) during absence seizures. The rate of fast ripples was associated with seizure frequency. HFO duration was significantly longer when co-occurring with spikes than when occurring independently, and the maximum frequency of HFOs co-occurring with spikes was higher than that of HFOs occurring independently. HFOs were predominantly localized in the medial prefrontal cortex (MPFC), whereas spikes were widespread to a variety of regions during the absence seizures. Compared with spikes, HFOs appeared to be more focal. The findings indicate that HFOs in the MPFC have a primary function in initializing epileptic activity in CAE.