Department of Complex Systems, Future University Hakodate Hakodate-shi, Hokkaido, Japan.
Front Hum Neurosci. 2013 May 17;7:208. doi: 10.3389/fnhum.2013.00208. eCollection 2013.
Theta band power (4-8 Hz) in the scalp electroencephalogram (EEG) is thought to be stronger during memory encoding for subsequently remembered items than for forgotten items. According to simultaneous EEG-functional magnetic resonance imaging (fMRI) measurements, the memory-dependent EEG theta is associated with multiple regions of the brain. This suggests that the multiple regions cooperate with EEG theta synchronization during successful memory encoding. However, a question still remains: What kind of neural dynamic organizes such a memory-dependent global network? In this study, the modulation of the EEG theta entrainment property during successful encoding was hypothesized to lead to EEG theta synchronization among a distributed network. Then, a transient response of EEG theta to a theta-band photic flicker with a short duration was evaluated during memory encoding. In the results, flicker-induced EEG power increased and decreased with a time constant of several hundred milliseconds following the onset and the offset of the flicker, respectively. Importantly, the offset response of EEG power was found to be significantly decreased during successful encoding. Moreover, the offset response of the phase locking index was also found to associate with memory performance. According to computational simulations, the results are interpreted as a smaller time constant (i.e., faster response) of a driven harmonic oscillator rather than a change in the spontaneous oscillatory input. This suggests that the fast response of EEG theta forms a global EEG theta network among memory-related regions during successful encoding, and it contributes to a flexible formation of the network along the time course.
头皮脑电图（EEG）中的θ波段功率（4-8 Hz）被认为在随后记住的项目的记忆编码过程中比遗忘的项目更强。根据同时进行的 EEG-功能磁共振成像（fMRI）测量，记忆相关的 EEG θ与大脑的多个区域相关。这表明，在成功的记忆编码过程中，多个区域与 EEG 同步的 θ波协同工作。然而，仍有一个问题悬而未决：什么样的神经动力学组织了这样一个依赖记忆的全局网络？在这项研究中，假设成功编码期间 EEG 同步的θ诱发电位特性的调制会导致分布式网络中的 EEG 同步。然后，在记忆编码期间评估了短暂持续时间的θ频闪光对 EEG 同步的瞬态响应。结果表明，闪光诱导的 EEG 功率在闪光的开始和结束后分别以几百毫秒的时间常数增加和减少。重要的是，在成功编码期间发现 EEG 功率的偏移响应显著降低。此外，相位锁定指数的偏移响应也与记忆表现相关。根据计算模拟，结果解释为受激谐波振荡器的时间常数较小（即响应较快），而不是自发振荡输入的变化。这表明，在成功编码过程中，EEG 同步的快速响应在记忆相关区域之间形成了一个全局 EEG 同步网络，并且它有助于沿着时间过程灵活地形成网络。
