Ge Man-Ling, Guo Jun-Dan, Chen Sheng-Hua, Zhang Ji-Chang, Fu Xiao-Xuan, Chen Yu-Min
The Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability, Department of Electrical Engineering, Hebei University of Technology, Tianjin 300130, China.
Sheng Li Xue Bao. 2017 Feb 25;69(1):77-88.
Epileptic spike is an indicator of hyper-excitability and hyper-synchrony in the neural networks. The inhibitory effects of spikes on theta rhythms (4-8 Hz) might be helpful to understand the mechanism of epileptic damage on the cognitive functions. To quantitatively evaluate the inhibitory effects of spikes on theta rhythms, intracerebral electroencephalogram (EEG) recordings with both sporadic spikes (SSs) and spike-free transient period between adjacent spikes were selected in 4 patients in the status of rapid eyes movement (REM) sleep with temporal lobe epilepsy (TLE) under the pre-surgical monitoring. The electrodes of hippocampal CA3 and entorhinal cortex (EC) were employed, since CA3 and EC built up one of key loops to investigate cognition and epilepsy. These SSs occurred only in CA3, only in EC, or in both CA3 and EC synchronously. Theta power was respectively estimated around SSs and during the spike-free transient period by Gabor wavelet transform and Hilbert transform. The intermittent extent was then estimated to represent for the loss of theta rhythms during the spike-free transient period. The following findings were obtained: (1) The prominent rhythms were in theta frequency band; (2) The spikes could transiently reduce theta power, and the inhibitory effect was severer around SSs in both CA3 and EC synchronously than that around either SSs only in EC or SSs only in CA3; (3) During the spike-free transient period, theta rhythms were interrupted with the intermittent theta rhythms left and theta power level continued dropping, implying the inhibitory effect was sustained. Additionally, the intermittent extent of theta rhythms was converged to the inhibitory extent around SSs; (4) The average theta power level during the spike-free transient period might not be in line with the inhibitory extent of theta rhythms around SSs. It was concluded that the SSs had negative effects on theta rhythms transiently and directly, the inhibitory effects aroused by SSs sustained during the spike-free transient period and were directly related to the intermittent extent. It was indicated that the loss of theta rhythms might qualify exactly the sustained inhibitory effects on theta rhythms aroused by spikes in EEG. The work provided an argumentation about the relationship between the transient negative impact of interictal spike and the loss of theta rhythms during spike-free activity for the first time, offered an intuitive methodology to estimate the inhibitory effect of spikes by EEG, and might be helpful to the analysis of EEG rhythms based on local field potentials (LFPs) in deep brain.
癫痫棘波是神经网络中兴奋性过高和同步性过高的一个指标。棘波对θ节律（4 - 8赫兹）的抑制作用可能有助于理解癫痫对认知功能损害的机制。为了定量评估棘波对θ节律的抑制作用，在术前监测下，从4例处于快速眼动（REM）睡眠状态的颞叶癫痫（TLE）患者中选取了既有散在棘波（SSs）又有相邻棘波间无棘波短暂期的脑内脑电图（EEG）记录。采用海马CA3区和内嗅皮质（EC）的电极，因为CA3和EC构成了研究认知和癫痫的关键环路之一。这些SSs仅出现在CA3区、仅出现在EC区或同时同步出现在CA3区和EC区。通过Gabor小波变换和希尔伯特变换分别估计SSs周围以及无棘波短暂期的θ功率。然后估计间歇性程度以表示无棘波短暂期内θ节律的缺失情况。得到以下结果：（1）主要节律在θ频段；（2）棘波可使θ功率短暂降低，且CA3区和EC区同步出现的SSs周围的抑制作用比仅在EC区或仅在CA3区的SSs周围的抑制作用更严重；（3）在无棘波短暂期，θ节律被打断，留下间歇性θ节律且θ功率水平持续下降，这意味着抑制作用持续存在。此外，θ节律间歇性程度与SSs周围的抑制程度趋于一致；（4）无棘波短暂期的平均θ功率水平可能与SSs周围θ节律的抑制程度不一致。得出结论：SSs对θ节律有短暂且直接的负面影响，SSs引起的抑制作用在无棘波短暂期持续存在且与间歇性程度直接相关。表明θ节律的缺失可能准确地反映了脑电图中棘波对θ节律的持续抑制作用。该研究首次为发作间期棘波的短暂负面影响与无棘波活动期间θ节律缺失之间的关系提供了论证，提供了一种通过脑电图估计棘波抑制作用的直观方法，并且可能有助于基于深部脑区局部场电位（LFPs）对脑电图节律进行分析。
