David Olivier, Woźniak Agata, Minotti Lorella, Kahane Philippe
Inserm, U836, Grenoble Institut des Neurosciences, CHU Grenoble-Bât E Safra-BP 217, Grenoble, France.
Neuroimage. 2008 Feb 15;39(4):1633-46. doi: 10.1016/j.neuroimage.2007.11.005. Epub 2007 Nov 21.
Short-term changes of intrinsic properties of neural networks play a critical role in brain dynamics. In that context, epilepsy is a typical pathology where the fast transition between interictal and ictal states is probably associated to intrinsic modifications of underlying networks. In this study, we focused on the correlates of plastic neural mechanisms in the intracerebral electroencephalogram (iEEG). Data were obtained during 1 Hz electrical stimulation in twenty patients suffering from temporal lobe epilepsy and implanted with intracerebral electrodes for clinical evaluation before resective surgery. First, we developed a procedure of analysis for localisation of the seizure onset zone based on brain excitability and plasticity defined as the average, and as the first-order (linear) modulation respectively, of the standard deviation of iEEG responses over stimulations. Our results suggest that the candidate epileptic focus is particularly prone to exhibiting short-term plasticity. Second, we used Dynamic Causal Modelling (DCM) to model explicitly short-term plasticity as a fast modulation of synaptic efficacies in either intrinsic or extrinsic connections to the focus. We found the two types of modulation both likely. Third, we used DCM to study the fast modulation of synaptic connectivity of long-range connections in neuronal networks restricted to the temporal lobe. Using DCM, we were able to estimate which structures expressed a strong modulatory input to the epileptic focus. Such early changes in interregional connectivity might be important for the initiation of electrically-induced seizures. They may also reflect some aspects of the pathogenesis of epilepsy in those patients.
神经网络内在特性的短期变化在脑动力学中起着关键作用。在这种背景下，癫痫是一种典型的病理状态，发作间期和发作期状态之间的快速转变可能与潜在网络的内在改变有关。在本研究中，我们聚焦于脑内脑电图（iEEG）中可塑性神经机制的相关因素。数据是在20例颞叶癫痫患者接受1Hz电刺激期间获得的，这些患者在切除性手术前已植入脑内电极用于临床评估。首先，我们基于脑兴奋性和可塑性开发了一种分析程序，分别将其定义为iEEG刺激反应标准差的平均值和一阶（线性）调制，用于癫痫发作起始区的定位。我们的结果表明，候选癫痫病灶特别容易表现出短期可塑性。其次，我们使用动态因果模型（DCM）将短期可塑性明确建模为与病灶内在或外在连接中突触效能的快速调制。我们发现这两种调制类型都有可能。第三，我们使用DCM研究局限于颞叶的神经元网络中远程连接的突触连接的快速调制。通过DCM，我们能够估计哪些结构对癫痫病灶表达了强烈的调制输入。区域间连接的这种早期变化可能对电诱导癫痫发作的起始很重要。它们也可能反映了这些患者癫痫发病机制的某些方面。
