Kalitzin Stiliyan, Parra Jaime, Velis Demetrios N, Lopes da Silva F H
Medical Physics Department, the Dutch Epilepsy Clinics Foundation (SEIN), Achterweg 5, 2103 SW Heemstede, The Netherlands.
IEEE Trans Biomed Eng. 2002 Nov;49(11):1279-86. doi: 10.1109/TBME.2002.804593.
A new analytical method for quantifying brain activity from magnetoelectroencephalogram (MEG) and electroencephalogram (EEG) recordings during periodic light stimulation is proposed. It consists in estimating the phase clustering of harmonically related frequency components of a subject's MEG/EEG responses evoked by the light stimulation. The method was developed to test the hypothesis that changes in the dynamics of brain systems in the course of intermittent photic stimulation (IPS) may precede the transition to seizure activity in photosensitive patients. We assumed that such changes would be reflected in the phase of harmonic components of the evoked responses. Thus, we determined the phase clustering for different harmonic components of these MEG/EEG signals. We found that the patients who develop epileptiform discharges during IPS present an enhancement of the phase clustering index at the gamma frequency band, compared with that at the driving frequency. We introduce a quantity--relative phase clustering index (rPCI)--by means of which this enhancement can be quantified. We argue that this quantity reflects the degree of excitability of the underlying dynamical system and it can indicate presence of nonlinear dynamics. rPCI can be applied to detect transitions to epileptic seizure activity in patients with known sensitivity to IPS.
提出了一种新的分析方法，用于量化周期性光刺激期间从脑磁图（MEG）和脑电图（EEG）记录中获取的大脑活动。该方法包括估计光刺激诱发的受试者MEG/EEG反应中谐波相关频率成分的相位聚类。该方法的开发是为了检验以下假设：在间歇性光刺激（IPS）过程中，大脑系统动力学的变化可能先于光敏患者癫痫发作活动的转变。我们假设这种变化会反映在诱发反应的谐波成分的相位中。因此，我们确定了这些MEG/EEG信号不同谐波成分的相位聚类。我们发现，在IPS期间出现癫痫样放电的患者，与驱动频率相比，其γ频段的相位聚类指数增强。我们引入了一个量——相对相位聚类指数（rPCI），通过它可以量化这种增强。我们认为这个量反映了潜在动力系统的兴奋程度，并且可以表明非线性动力学的存在。rPCI可用于检测已知对IPS敏感的患者向癫痫发作活动的转变。
