Neru Arun, Assisi Collins
Division of Biology, Indian Institute of Science Education and Research, Pune 411008, India
eNeuro. 2021 Jun 17;8(3). doi: 10.1523/ENEURO.0059-20.2021. Print 2021 May-Jun.
Stability and precision of sequential activity in the entorhinal cortex (EC) is crucial for encoding spatially guided behavior and memory. These sequences are driven by constantly evolving sensory inputs and persist despite a noisy background. In a realistic computational model of a medial EC (MEC) microcircuit, we show that intrinsic neuronal properties and network mechanisms interact with theta oscillations to generate reliable outputs. In our model, sensory inputs activate interneurons near their most excitable phase during each theta cycle. As the inputs change, different interneurons are recruited and postsynaptic stellate cells are released from inhibition. This causes a sequence of rebound spikes. The rebound time scale of stellate cells, because of an -current, matches that of theta oscillations. This fortuitous similarity of time scales ensures that stellate spikes get relegated to the least excitable phase of theta and the network encodes the external drive but ignores recurrent excitation. In contrast, in the absence of theta, rebound spikes compete with external inputs and disrupt the sequence that follows. Further, the same mechanism where theta modulates the gain of incoming inputs, can be used to select between competing inputs to create transient functionally connected networks. Our results concur with experimental data that show, subduing theta oscillations disrupts the spatial periodicity of grid cell receptive fields. In the bat MEC where grid cell receptive fields persist even in the absence of continuous theta oscillations, we argue that other low frequency fluctuations play the role of theta.
内嗅皮层（EC）中序列活动的稳定性和精确性对于编码空间导向行为和记忆至关重要。这些序列由不断变化的感觉输入驱动，尽管存在嘈杂的背景仍能持续存在。在一个内侧内嗅皮层（MEC）微电路的真实计算模型中，我们表明内在神经元特性和网络机制与θ振荡相互作用以产生可靠输出。在我们的模型中，感觉输入在每个θ周期内接近其最易兴奋阶段时激活中间神经元。随着输入的变化，不同的中间神经元被招募，突触后星状细胞从抑制中释放。这导致一系列反弹尖峰。由于一种电流，星状细胞的反弹时间尺度与θ振荡的时间尺度相匹配。这种时间尺度的偶然相似性确保星状尖峰被分配到θ的最不易兴奋阶段，并且网络编码外部驱动但忽略反复激发。相比之下，在没有θ的情况下，反弹尖峰与外部输入竞争并扰乱随后的序列。此外，θ调节传入输入增益的相同机制可用于在竞争输入之间进行选择，以创建瞬态功能连接网络。我们的结果与实验数据一致，实验数据表明，抑制θ振荡会破坏网格细胞感受野的空间周期性。在蝙蝠的MEC中，即使在没有连续θ振荡的情况下网格细胞感受野仍然存在，我们认为其他低频波动起到了θ的作用。
