Center for Functional and Molecular Imaging, Department of Neurology Georgetown University, 3900 Reservoir Road, NW, Washington, DC 20057-1488, USA.
Int J Neural Syst. 2011 Apr;21(2):103-14. doi: 10.1142/S0129065711002699.
Even though recent studies have suggested that seizures do not occur suddenly and that before a seizure there is a period with an increased probability of seizure occurrence, neurophysiological mechanisms of interictal and pre-seizure states are unknown. The ability of mathematical methods to provide much more sensitive tools for the detection of subtle changes in the electrical activity of the brain gives promise that electrophysiological markers of enhanced seizure susceptibility can be found even during interictal periods when EEG of epilepsy patients often looks 'normal'. Previously, we demonstrated in animals that hippocampal and neocortical gamma-band rhythms (30-100 Hz) intensify long before seizures caused by systemic infusion of kainic acid. Other studies in recent years have also drawn attention to the fast activity (>30 Hz) as a possible marker of epileptogenic tissue. The current study quantified gamma-band activity during interictal periods and seizures in intracranial EEG (iEEG) in 5 patients implanted with subdural grids/intracranial electrodes during their pre-surgical evaluation. In all our patients, we found distinctive (abnormal) bursts of gamma activity with a 3 to 100 fold increase in power at gamma frequencies with respect to selected by clinicians, quiescent, artifact-free, 7-20 min "normal" background (interictal) iEEG epochs 1 to 14 hours prior to seizures. Increases in gamma activity were largest in those channels which later displayed the most intensive electrographic seizure discharges. Moreover, location of gamma-band bursts correlated (with high specificity, 96.4% and sensitivity, 83.8%) with seizure onset zone (SOZ) determined by clinicians. Spatial localization of interictal gamma rhythms within SOZ suggests that the persistent presence of abnormally intensified gamma rhythms in the EEG may be an important tool for focus localization and possibly a determinant of epileptogenesis.
尽管最近的研究表明癫痫发作不会突然发生，并且在癫痫发作前有一个癫痫发作发生概率增加的时期，但癫痫发作间期和发作前状态的神经生理机制尚不清楚。数学方法的能力为检测大脑电活动的细微变化提供了更敏感的工具，这使得即使在癫痫患者的脑电图在癫痫发作间期通常看起来“正常”的情况下，也有可能找到增强癫痫易感性的电生理标志物。以前，我们在动物中证明，在系统性注射海人酸引起癫痫发作之前，海马和新皮层的γ波段节律（30-100 Hz）就会强烈增强。近年来的其他研究也引起了对快速活动（>30 Hz）作为致痫组织可能标志物的关注。目前的研究在 5 名接受颅内脑电图（iEEG）植入的患者中，对癫痫发作间期和癫痫发作期间的γ波段活动进行了量化，这些患者在手术前评估期间植入了硬膜下网格/颅内电极。在我们所有的患者中，我们发现了独特的（异常）γ活动爆发，与由临床医生选择的、静止的、无伪影的、7-20 分钟的“正常”背景（癫痫发作间期）iEEG 时段相比，γ频率的功率增加了 3 到 100 倍。在这些通道中，γ活动的增加最大，这些通道后来显示出最强烈的脑电图癫痫发作放电。此外，γ波段爆发的位置与临床医生确定的癫痫发作起始区（SOZ）相关（特异性为 96.4%，敏感性为 83.8%）。SOZ 内癫痫发作间期γ节律的空间定位表明，脑电图中异常增强的γ节律的持续存在可能是焦点定位的重要工具，并且可能是癫痫发生的决定因素。
