A Study In Characteristic Pattern Of Intracranial High Frequency ECoGs Network In Epileptic Seizure

Epilepsy,a chronic central nervous system disease caused by abnormal highly synchronized discharge of brain neurons,has a high incidence in the world and in our country.After regular treatment with antiepileptic drugs,most patients can be relieved obviously,but still some patients aren`t sensitive to antiepileptic drugs which become patients with refractory epilepsy.Method of epileptic foci excision to reduce seizures or even reach seizure-free state has become an effective treatment for refractory epilepsy,while the accurate location of epilepsy foci is the most important link in the efficacy of epileptogenic resection.Therefore,the accurate positioning of epileptic foci has become one of the key research focus of researchers.In recent years,with the rapid development of Electrophysiology,high-frequency oscillations(HFOs)has been confirmed that its closely related with epileptic seizures.HFOs mainly contain the Γband(30Hz-80Hz),the R band(80Hz-250Hz)and the Fast-R band(250Hz-500Hz).It`s of great scientific and clinical significance in both epileptogenic mechanism and location of epileptic foci.Purpose: In order to analyze the role of HFOs in accurate localization of epileptic foci and the potential neural mechanism.In this study,the subjects are multi-channel ECoGs in the ictal period of myoclonic seizures from 5 pre-surgical removal of epileptic foci patients.The characteristic models of each band network are calculated by Granger causality analysis,low-frequency bands contain:δ band(0Hz-4Hz),θ band [4Hz-8Hz),α band [8Hz-12Hz)and β band [12Hz-30Hz).High-frequency oscillations include: γ band [30Hz-80Hz),R band [80Hz-250Hz)and F-R band [250Hz-500Hz).By comparing the differences between low-frequency bands and high-frequency oscillations,we can investigate the characteristics of HFOs in epileptic seizures.Methods:1.Data: The data were provided by Xuanwu hospital of Capital Medical University.The data were ictal and interictal multichannel ECoGs from 5preoperative patients with epileptic foci resection.2.Preprocessing of ECoGs: Remove the power frequency interference and baseline drift in the original ECoGs.3.Constructing the internal brain network: According to the Granger causal connectivity analysis,calculating the time distribution pattern of DTF on each band within each brain region during ictal period.Then selecting the characteristic period,calculating the frequency variation pattern and spatial distribution pattern of DTF on each band within brain region during characteristic period.4.Constructing the interval brain network: Selecting the channels which DTF are above the average DTF,constructing the interval brain network,calculating the frequency variation pattern and spatial distribution pattern of DTF on each band among brain regions during characteristic period.5.Comparison between ictal and interictal brain network: Same method to construct the interval brain network,calculating the interictal DTF of interval brain network on each band,comparing the differences between ictal and interictal DTF.Results:1.According to the characteristic of each patient`s frequency variation pattern within regions during the characteristic ictal period,the peaks of DTF are located in HFOs.In terms of the characteristic of each patient`s frequency variation pattern between regions during the characteristic ictal period,the peaks of DTF are also located in HFOs.2.According to the characteristic of each patient`s spatial distribution pattern of the DTF within or between the regions,the location of low-frequency bands and HFOs are quite different.There are common nodes in the distribution of low-frequency band and HFOs while HFOs have unique nodes.3.By comparing the DTF between ictal and interictal period,DTF of each band in ictal period is significantly higher than in interictal period(t-test,p<0.05).Conclusions:1.Our results indicate that the connectivity strength of HFOs is higher than low-frequency bands..2.In the localization of epileptic foci,the distribution of HFOs and low-frequency bands are quite different.The unique nodes of HFOs may indicate the potential epileptic zone.3.The intensity of connection in each frequency band in ictal period is significantly higher than that in the interictal period.