Neuroscience Doctoral Program, George Mason University, Fairfax, VA, 22030, USA,
Cogn Neurodyn. 2007 Sep;1(3):237-48. doi: 10.1007/s11571-007-9018-9. Epub 2007 Apr 12.
The origins and functional significance of theta phase precession in the hippocampus remain obscure, in part, because of the difficulty of reproducing hippocampal place cell firing in experimental settings where the biophysical underpinnings can be examined in detail. The present study concerns a neurobiologically based computational model of the emergence of theta phase precession in which the responses of a single model CA3 pyramidal cell are examined in the context of stimulation by realistic afferent spike trains including those of place cells in entorhinal cortex, dentate gyrus, and other CA3 pyramidal cells. Spike-timing dependent plasticity in the model CA3 pyramidal cell leads to a spatially correlated associational synaptic drive that subsequently creates a spatially asymmetric expansion of the model cell's place field. Following an initial training period, theta phase precession can be seen in the firing patterns of the model CA3 pyramidal cell. Through selective manipulations of the model it is possible to decompose theta phase precession in CA3 into the separate contributing factors of inheritance from upstream afferents in the dentate gyrus and entorhinal cortex, the interaction of synaptically controlled increasing afferent drive with phasic inhibition, and the theta phase difference between dentate gyrus granule cell and CA3 pyramidal cell activity. In the context of a single CA3 pyramidal cell, the model shows that each of these factors plays a role in theta phase precession within CA3 and suggests that no one single factor offers a complete explanation of the phenomenon. The model also shows parallels between theta phase encoding and pattern completion within the CA3 autoassociative network.
海马体中θ 相位进动的起源和功能意义仍然不清楚，部分原因是难以在实验环境中重现海马体位置细胞的放电，而在这些实验环境中可以详细研究生物物理基础。本研究涉及一个基于神经生物学的海马体θ 相位进动出现的计算模型，在该模型中，单个模型 CA3 锥体神经元的反应在受到包括海马体、齿状回和其他 CA3 锥体神经元中的位置细胞在内的实际传入尖峰序列刺激的情况下进行了检查。模型 CA3 锥体神经元中的尖峰时间依赖性可塑性导致空间相关的联想性突触驱动，随后导致模型细胞的位置场的空间不对称扩展。在初始训练期后，可以在模型 CA3 锥体神经元的放电模式中看到θ 相位进动。通过对模型的选择性操作，可以将 CA3 中的θ 相位进动分解为来自齿状回和海马体上游传入的遗传、突触控制的传入驱动与相性抑制的相互作用以及齿状回颗粒细胞和 CA3 锥体神经元活动之间的θ 相位差等单独因素。在单个 CA3 锥体神经元的背景下，该模型表明这些因素中的每一个都在 CA3 中的θ 相位进动中发挥作用，并表明没有一个单一因素可以完全解释这一现象。该模型还表明在 CA3 自联想网络中θ 相位编码和模式完成之间存在相似之处。
