Characterization of High Frequency Oscillations propagation networks and application to childhood refractory epilepsy

Abstract

Refractory epilepsy is a central nervous system disorder that cannot be treated with drugs. This condition causes frequent and spontaneous seizures. Recently, research on this topic has highlighted the importance of pathological highfrequency oscillations (HFO) which have a frequency range from 80 to 450 Hz. These waves are seen in the records of neuronal electrical activity in these patients. Thanks to these waves, the epileptogenic zone (EZ) essential for the treatment of epilepsy can be found. However, there is controversy within studies in this field about whether or not there is a spread of HFOs, as is the case with epileptiform activity and ictal activity. Methodology: HFOs are detected in SEEG recordings during the sleep of three patients with refractory epilepsy. We analyzed the temporal overlap of HFOs in the seizure onset zone(SOZ) with the other channels, that is, we analyzed all HFOs detected in one SOZ channel with the other channels. These possible propagations are analyzed by connectivity measures (correlation, coherence, mutual information and correlation of the Stockwell spectrum) and also with a temporal and frequency visualization. Results: Visually we see some cases that correspond to propagation due to HFO being superimposed on different electrodes with a delay, there is a similar morphology and also there is an equal frequency range in the spectrum. They do not spread in all cases. There are some channels that get higher connectivity values. All connectivity measures tend to follow the same pattern and correlate with the number of HFOs superimposed on the channel. Conclusion: It has been shown that there are some cases of HFO overlap where there is clearly a propagation, but this is not seen in all the cases, but there are some channels that are more interrelated during periods where there is HFO.