Liu Zilu, Wang Qingyun, Han Fang
Department of Dynamics and Control, Beihang University, Beijing, China.
College of Information Science and Technology, Donghua University, Shanghai, China.
Front Comput Neurosci. 2022 Feb 4;16:791189. doi: 10.3389/fncom.2022.791189. eCollection 2022.
Theta rhythms (4-12 Hz) in the hippocampus are thought to be associated with cognitive functions such as memory processing and spatial navigation. Rhythmic oscillations in the neural system can be induced by synchronization of neural populations, while physiological mechanisms for the emergence, modulation, and regulation of such rhythms are not fully understood. Conceptual reduced models are promising in promoting current understandings toward neural synchronization because of high computational efficiency, while they appear less straightforward in biological relevance. In this study, we use a hybrid E-I network as a conceptual model of the hippocampus to investigate the dynamics of synchronous theta oscillations. Specifically, experimentally constrained Izhikevich neurons and preferential connections among neural groups specific to hippocampal CA1 are incorporated to enhance the biological relevance of the model network. Based on such a model, synaptic factors related to the balance of network excitation and inhibition are the main focus of present study. By careful parameter exploration, the distinct role of synaptic connections in theta rhythm generation, facilitation of synchronization, and induction of burst activities are clarified. It is revealed that theta rhythms can be present with AMPA mediated weak E-I couplings, or with strong NMDA current. Moreover, counter-inhibition, namely inhibition of inhibition, is found effective in modulating the degree of network synchronization, while has little effect on regulating network frequency in both regimes. Under pathological considerations where the effect of pyramidal sprouting is simulated, synchronized burst patterns are observed to be induced by elevated recurrent excitation among pyramidal cells. In the final part, we additionally perform a test on the robustness of our results under heterogeneous parameters. Our simulation results may provide insights into understanding how brain rhythms are generated and modulated, and the proposed model may serve as a useful template in probing mechanisms of hippocampal-related dynamics.
海马体中的θ节律（4-12赫兹）被认为与认知功能相关，如记忆处理和空间导航。神经系统中的节律性振荡可由神经群体的同步化诱导产生，然而，这种节律出现、调制和调节的生理机制尚未完全明确。概念性简化模型因其高计算效率，有望促进当前对神经同步化的理解，但其生物学相关性似乎不那么直接。在本研究中，我们使用混合E-I网络作为海马体的概念模型，以研究同步θ振荡的动力学。具体而言，纳入了实验约束的Izhikevich神经元以及海马体CA1特有的神经群体之间的优先连接，以增强模型网络的生物学相关性。基于这样一个模型，与网络兴奋和抑制平衡相关的突触因素是本研究的主要关注点。通过仔细的参数探索，阐明了突触连接在θ节律产生、同步促进和爆发活动诱导中的独特作用。结果表明，θ节律可在AMPA介导的弱E-I耦合或强NMDA电流存在的情况下出现。此外，反抑制，即抑制抑制，被发现对调节网络同步程度有效，而在两种情况下对调节网络频率几乎没有影响。在模拟锥体芽生效应的病理情况下，观察到锥体细胞之间反复兴奋增强会诱导同步爆发模式。在最后一部分，我们还对结果在异质参数下的稳健性进行了测试。我们的模拟结果可能为理解脑节律如何产生和调制提供见解，并且所提出的模型可能作为探索海马体相关动力学机制的有用模板。
