Department of Brain Science and Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino Wakamatsu-ku, Kitakyushu, 808-0196, Japan,
Cogn Neurodyn. 2007 Jun;1(2):169-84. doi: 10.1007/s11571-006-9003-8. Epub 2006 Oct 31.
We investigated successive firing of the stellate cells within a theta cycle, which replicates the phase coding of place information, using a network model of the entorhinal cortex layer II with loop connections. Layer II of the entorhinal cortex (ECII) sends signals to the hippocampus, and the hippocampus sends signals back to layer V of the entorhinal cortex (ECV). In addition to this major pathway, projection from ECV to ECII also exists. It is, therefore, inferred that reverberation activity readily appears if projections from ECV to ECII are potentiated. The frequency of the reverberation would be in a gamma range because it takes signals 20-30 ms to go around the entorhinal-hippocampal loop circuits. On the other hand, it has been suggested that ECII is a theta rhythm generator. If the reverberation activity appears in the entorhinal-hippocampal loop circuits, gamma oscillation would be superimposed on a theta rhythm in ECII like a gamma-theta oscillation. This is a reminiscence of the theta phase coding of place information. In this paper, first, a network model of ECII will be developed in order to reproduce a theta rhythm. Secondly, we will show that loop connections from one stellate cell to the other one are selectively potentiated by afferent signals to ECII. Frequencies of those afferent signals are different, and transmission delay of the loop connections is 20 ms. As a result, stellate cells fire successively within one cycle of the theta rhythm. This resembles gamma-theta oscillation underlying the phase coding. Our model also replicates the phase precession of stellate cell firing within a cycle of subthreshold oscillation (theta rhythm).
我们研究了在一个 theta 周期内星状细胞的连续放电，该周期复制了位置信息的相位编码，使用具有环路连接的内嗅皮层 II 层的网络模型。内嗅皮层 II 层（ECII）向海马体发送信号，海马体向内嗅皮层 V 层（ECV）发送信号。除了这条主要途径之外，ECV 到 ECII 的投射也存在。因此，如果从 ECV 到 ECII 的投射被增强，就可以推断出易出现回响活动。由于信号在环绕内嗅皮质-海马环路电路时需要 20-30 毫秒，因此，回响的频率将处于伽马范围内。另一方面，有人提出 ECII 是 theta 节律发生器。如果回响活动出现在内嗅皮质-海马环路电路中，那么在 ECII 中，伽马振荡将叠加在 theta 节律上，形成 gamma-theta 振荡。这让人想起了位置信息的 theta 相位编码。在本文中，首先，我们将开发一个 ECII 的网络模型，以重现 theta 节律。其次，我们将展示来自一个星状细胞到另一个星状细胞的环路连接通过 ECII 的传入信号被选择性地增强。这些传入信号的频率不同，环路连接的传输延迟为 20 毫秒。结果，星状细胞在一个 theta 节律周期内相继放电。这类似于theta 节律下的 gamma-theta 振荡，为相位编码提供基础。我们的模型还复制了在亚阈值振荡（theta 节律）周期内星状细胞放电的相位超前。
