The input-output transformation of the hippocampal granule cells: from grid cells to place fields.
The input-output transformation of the hippocampal granule cells: from grid cells to place fields.
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DOI：
10.1523/jneurosci.6048-08.2009
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发表时间：
2009-06-10
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影响因子：
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通讯作者：
Lisman JE
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文献类型：
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作者：
de Almeida L;Idiart M;Lisman JE
大鼠内侧内嗅皮层的网状细胞在整个环境中(周期性地)放电。这些细胞为海马颗粒细胞提供输入，其输出的特征是一个或多个小的位置场。我们试图理解这种投入-产出转换是如何发生的。现有信息允许在没有自由可调参数的情况下模拟这一过程。我们首先研究了颗粒细胞中激发的空间分布，这是由随机选择的网格细胞的兴奋输入会聚而产生的。因为最终的总和取决于输入的数量，所以有必要使用一个实际的数字(~1200)，并考虑到它们在强度上的20倍变化。由此产生的激发图只有适度的峰谷。为了分析这种兴奋如何与抑制相互作用，我们利用了E%-max赢家通吃规则，该规则描述了伽马频率抑制如何影响放电。我们发现，模拟的颗粒细胞有发射图，其中有一个或多个位场，其大小和数量与实验观察到的位场相似。根据实验观察，很大一部分颗粒细胞没有位场。由于输入的放电频率和突触特性是已知的，因此可以计算出进入颗粒细胞的兴奋性电荷(2-3pC)，并发现仅略大于激发颗粒细胞所需的电荷(1pC)。我们的结论是，齿状颗粒的输入-输出转换并不强烈地依赖于突触的修饰；位场的形成可以用随机选择的兴奋性输入的简单求和来理解，并结合赢家通吃的网络机制。
Grid cells in the rat medial entorhinal cortex fire (periodically) over the entire environment. These cells provide input to hippocampal granule cells whose output is characterized by one or more small place fields. We sought to understand how this input-output transformation occurs. Available information allows simulation of this process with no freely adjustable parameters. We first examined the spatial distribution of excitation in granule cells produced by the convergence of excitatory inputs from randomly chosen grid cells. Because the resulting summation depends on the number of inputs, it is necessary to use a realistic number (~1200) and to take into consideration their 20-fold variation in strength. The resulting excitation maps have only modest peaks and valleys. To analyze how this excitation interacts with inhibition, we utilized an E%-max winner-take-all rule that describes how gamma-frequency inhibition affects firing. We found that simulated granule cells have firing maps that have one or more place fields whose size and number approximates those observed experimentally. A substantial fraction of granule cells have no place fields, as observed experimentally. Because the input firing rates and synaptic properties are known, the excitatory charge into granule cells could be calculated (2–3 pC) and was found to be only somewhat larger than required to fire granule cells (1 pC). We conclude that the input-output transformation of dentate granule does not depend strongly on synaptic modification; place field formation can be understood in terms of simple summation of randomly chosen excitatory inputs, in conjunction with a winner-take-all network mechanism.