Frequency coupling in nervous system is believed to be associated with normal and impaired brain functions. However, most of the existing experiments have been concentrated on the coupling strength within frequency bands, while the coupling strength between different bands is ignored. In this work, we apply phase synchronization index (PSI) to investigate the cross-frequency coupling (CFC) of Electroencephalogram (EEG) signals. The PSI matrixes for the multi-channel EEG signals are calculated from interictal to ictal period in each sliding time window. The results show that CFC changes obviously once seizure occurs between the different bands, and such alteration is earlier than the appearance of clinical symptoms in seizure. Considering the similar role of the within-frequency coupling (WFC), we further reconstruct multi-layered brain networks, including CFC networks and WFC networks. The graph metrics are applied to investigate the variation of network structure of the epileptic brain. Significant decreases/increases of the local/global efficiency are found in δ–β, δ–α, θ–α and δ–θ bands from the CFC network, while WFC network shows a significant decline in the local efficiency in θ and α bands. These findings suggest that CFC may provide a new perspective to observe the alteration of brain structure when seizure occurs, and the investigation of functional connectivity across the full frequency spectrum can give us a deeper understanding of epileptic brains.

中文翻译：

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癫痫发作时大脑功能连接的变化：跨频相位同步的脑电图分析


神经系统中的频率耦合被认为与正常和受损的大脑功能有关。然而，现有的实验大多集中在频段内的耦合强度，而忽略了不同频段之间的耦合强度。在这项工作中，我们应用相位同步指数（PSI）来研究脑电图（EEG）信号的跨频耦合（CFC）。多通道 EEG 信号的 PSI 矩阵是在每个滑动时间窗口中从发作间期到发作期计算的。结果表明，不同带之间一旦发生癫痫发作，CFC就会发生明显变化，且这种变化早于癫痫发作时临床症状的出现。考虑到同频耦合（WFC）的类似作用，我们进一步重建了多层大脑网络，包括CFC网络和WFC网络。图度量用于研究癫痫大脑网络结构的变化。 CFC 网络的 δ–β、δ–α、θ–α 和 δ–θ 频段局部/全局效率显着下降/上升，而 WFC 网络的 θ 和 α 频段局部效率显着下降。这些发现表明，CFC可能为观察癫痫发生时大脑结构的变化提供新的视角，而对全频谱功能连接的研究可以让我们更深入地了解癫痫大脑。