Theta-paced flickering between place-cell maps in the hippocampus
Theta-paced flickering between place-cell maps in the hippocampus
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DOI：
10.1038/nature10439
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发表时间：
2011-10-13
期刊：
影响因子：
64.8
通讯作者：
Moser, May-Britt
中科院分区：
文献类型：
--
作者：
Jezek, Karel;Henriksen, Espen J.;Moser, May-Britt
回忆离散记忆的能力被认为取决于递归神经网络中吸引子状态的形成（1 - 4）。在这类网络中，当记忆被编码时存在的线索子集能够可靠地重新激活相关表征，同时来自竞争表征的干扰被最小化。理论研究指出海马体的递归CA3系统可能是一个吸引子网络（3，4）。与这些研究的预测一致，实验表明CA3和下游CA1中的位置表征能容忍环境配置的微小变化，但当差异变大时会转换为不相关的表征（5 - 9）。然而，在亚秒级时间尺度上支持这种网络转换的动力学机制还鲜为人知。在此我们通过大鼠实验表明，空间环境的瞬时改变并不会立刻改变海马体的表征，而是会在CA3神经元集群的放电活动中出现暂时的双稳态。CA3网络不是通过一系列中间活动状态逐渐过渡，而是在确定为当前环境表征之前，在过去和当前环境的预先形成的表征之间经历一段短暂的竞争性闪烁。网络闪烁极其迅速，通常从一个θ周期到下一个θ周期，活跃的神经元集群就会完全更替。在单个周期内，当放电开始减弱时，在周期末尾的分离更强，这表明θ周期是海马体中吸引子状态表达的一个时间单位。在连续的θ周期中重复模式完成过程可能有助于纠错，并在存在微弱和模糊的输入线索时提高辨别能力。
The ability to recall discrete memories is thought to depend on the formation of attractor states in recurrent neural networks(1-4). In such networks, representations can be reactivated reliably from subsets of the cues that were present when the memory was encoded, at the same time as interference from competing representations is minimized. Theoretical studies have pointed to the recurrent CA3 system of the hippocampus as a possible attractor network(3,4). Consistent with predictions from these studies, experiments have shown that place representations in CA3 and downstream CA1 tolerate small changes in the configuration of the environment but switch to uncorrelated representations when dissimilarities become larger(5-9). However, the kinetics supporting such network transitions, at the subsecond timescale, is poorly understood. Here we show in rats that instantaneous transformation of the spatial context does not change the hippocampal representation all at once but is followed by temporary bistability in the discharge activity of CA3 ensembles. Rather than sliding through a continuum of intermediate activity states, the CA3 network undergoes a short period of competitive flickering between preformed representations of the past and present environment before settling on the latter. Network flickers are extremely fast, often with complete replacement of the active ensemble from one theta cycle to the next. Within individual cycles, segregation is stronger towards the end, when firing starts to decline, pointing to the theta cycle as a temporal unit for expression of attractor states in the hippocampus. Repetition of pattern-completion processes across successive theta cycles may facilitate error correction and enhance discriminative power in the presence of weak and ambiguous input cues.