| Temporal lobe epilepsy(TLE)is a common disorder of nervous system structure and function,which main seizure focus appear in the hippocampus-related brain regions of the medial temporal lobe.Electroencephalogram(EEG)is one of the main methods of traditional epilepsy research owing to the Abnormal excitatory neuroelectrical activity during the epileptic seizures.High frequency oscillations(HFOs)refer to the local field potential(LFP)formed by 80-250 Hz ripple and 250-500 Hz fast ripple,which is considered as the more accurate epilepsy biomarker in clinical diagnosis of epilepsy.However,the spatial distribution,signal characteristics,and mechanism of generation of HFOs in the hippocampal brain region remain unclear so far and needs further clarification.This paper analysed the conventional electroencephalographic characteristics and the HFOs’ spatial distribution of the hippocampal neural circuit during seizures,which is based on the local field potential recorded in the pilocarpine-induced temporal lobe epilepsy rat model.The main results are analyzed as follows:1.EEG power spectrum analysis found that: 1)During epileptic seizures,energy was significantly increased during the grand mal seizures and decreased after seizures ended.With the onset and termination of seizures,energy gradually shifts from the θ-band to the δ-band,showing a gradual decreasing trend;2)During the grand mal seizures,the energy of higher-frequency γ-band was suppressed,and was significantly higher in CA1,dentate gyrus and CA3 rather than the subiculum,entorhinal cortex,and temporal lobe.It was suggested that the hippocampal neural circuit may be reconstructed during seizures,and the electroencephalogram of higher frequency may be more specific about brain areas.2.Coherent analysis found that 1)During the epileptic seizure,hypersynchronous neuronal discharges in the brain region appeared more frequently in the pre-onset and termination of seizures;2)The degree analysis based on the coherence found that the shallow brain regions in the hippocampal neural circuit may have higher functional connectivity,playing a more important role in this loop.3.HFOs analysis found that 1)The frequency of HFOs events is inversely proportional to the duration and the times of oscillations in each event is about 4;2)The change of fast ripple features was consistent in the pre-seizure stage,suggesting that fast ripple may play a predictive role in epileptic seizures.;3)The appearance of the ripples in all brain regions is inhibited except for the subiculum during epileptic seizures,suggesting that the subiculum may be an important brain region which can inhibit seizures.By contrast,the fast ripples in the brain regions of the hippocampal neural circuits increased significantly,but rate of synchronization of fast ripples in two brain regions was low,suggesting that the synchronization of the brain regions during large seizures may not be high,which was consistent with the coherence analysis;4)Ripple was mainly distributed in the brain area of CA1 in the baseline state,while fast ripple was mainly distributed in the brain area of CA3 in the grand mal seizures.Combined with the analysis of the degree,it indicated that the epilepsy focus may appear in the deeper brain area with weak functional connectivity and high-frequency oscillations were more accurate as the new biomarkers compared with lower frequency;5)The HFOs of the HYP and LVF epilepsy subtypes were different in quantity and trend,suggesting that they may have different generation mechanism,which was worth further study.This article analyzed the electrophysiological characteristics of the hippocampal neural network during temporal lobe epileptic seizures from the point of view of the electrophysiological,and discussed the relationship between HFOs and epileptic seizure in related brain regions.It was indicated that HFOs would have characteristic changes in the seizure process and could provide a new idea for studying the mechanism of temporal lobe epilepsy. |
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