Functional Connectivity Network Of Eeg’s Delta-band In Epilepsy Interictal ED Via MVAR Granger Causality Analysis

ObjectiveDuring interictal epileptiform discharges (ED) in temporal lobe epilepsy (TLE), δ band of EEG may be correlated to the outburst of seizure. However, no over-discharges causal relationship was found in previous studies in δ band EEGs of different brain regions during interictal period. The aim of this study is to investigate functional connectivity of16-channel EEGs in δ band based on multivariate autoregressive (MVAR) model Granger Causality analysis, and to provide support for the study of the hyper-discharges mechanism of TLE.Methods1. Experimental data:16-channel EEG data in this paper are provided by Tianjin Neurological Institute. The data were recorded from18subjects (9with TLE,9normals), and were divided into three groups:epileptiform discharge ED group, non-ED group and control group.10segments of20s duration signals were extracted from each group of subject.2. Preprocessing:there are three groups:epileptiform discharge ED group, non-ED group and control group. Remove the trend from each channel to obtain zero-mean signals.3. Short Time Fourier Transform (STFT) is used to analyze time-frequency characteristics of EEGs. The mean energy distribution of16-channels in each segment is computed.4. Bandpass filter is used to extract different bands of signals, in which δ band is in0.5-4Hz.5. Multi-channel Granger causality analysis was used to analysis δ band EEGsBased on MVAR model Granger causality analysis, the functional connection between δ band of each epileptiform segments were analyzed, especially between areas of inferoposterior temporal lobe (left:T5, right:T6), frontal lobe (Fp1, Fp2, F3, F4) and parietal lobe (C3, C4).(1) Directed Transfer Function, DTFMean γδ for each subject is calculated to compare functional connection in ED group, non-ED group and normal group.(2) Directed Causality, DCDCs were calculated to verity the causality of each node. And then the causal relationship network diagrams are obtained.(3) Betweenness Centrality, BCBCs were calculated between each node and T5/T6, nodes of most importance in the causality network were analyzed in ED group, non-ED group and normal group respectively.Results1. During the temporal lobe epilepsy epileptiform discharges, multi-channel EEGs’energy concentrates on the0.5～15Hz.δ band (0.5～4Hz),0band(5～8Hz), α band(9～12Hz),βband(13～30Hz).2.δ band of EEG(1)DTFγδ in ED group from inferoposterior temporal lobe (left:T5, right:T6) to frontal lobe (Fpl, Fp2, F3, F4), and parietal lobe (C3, C4) is the highest in the network:γδfrom6Left-TLE patients in ED group (from T5to frontal lobe, parietal lobe):0.1323±0.0329-0.1670±0.0289;γδ from3Left-TLE patients in ED group (from T6to frontal lobe, parietal lobe):0.1383±0.0204～0.1633±0.0431;γδ from9normal subjects (from T5/T6to frontal lobe, parietal lobe):0.0217±0.0087～0.0757±0.0074; γδ from2patients in non-ED group (from T5/T6to frontal lobe, parietal lobe):0.0132±0.0029～0.0197±0.0024.(2) DCDCs calculated with directed transfer function assessed the authenticity of the causal relationship among each node.The DCs are in0.0571～0.1774.(3)BCThe nodes with the highest BCs in ED group are in.frontal lobe (Fpl,Fp2, F3, F4), which ranges from0.5to0.67; in control group are between0and0.02; in non-ED group are between0and0.12.5. In ED group, y for0and a band (form T5/T6to frontal lobe and parietal lobe) are the highest in the network, which ranges from0.1346±0.0118to0.1741±0.0111. The highest BC nodes are in frontal lobe (Fpl,Fp2, F3, F4), with values between0.5and0.66, the results and8band EEGs’results are at the same level.β band of EEGs’ γδ are in0.1374±0.0133～0.1677±0.0112.Conclusions:1. In ED group, hyper-discharges in8band transferred from inferoposterior temporal lobe to frontal and parietal lobe, demonstrated strong connection between inferoposterior temporal lobe and frontal/parietal lobe which may form functional network related to seizure. The results and0, a bands EEGs’results are at the same level.2. In control group, no causality functional network was shown in8band.3. In non-ED group, weak connection between inferoposterior temporal lobe and frontal/parietal lobe was shown, which may form weak causality functional network.4. In other bands such as θ and a band, strong connection between inferoposterior temporal lobe and frontal/parietal lobe was shown. The results and8band EEGs’results are at the same level. There is no functional network in β band.