齿状回建立的空间CA3表征信息量有多大？
How informative are spatial CA3 representations established by the dentate gyrus?
摘要：
在哺乳动物海马中，齿状回（DG）的特点是稀疏和强大的单向投射到CA3锥体细胞，所谓的苔藓纤维。苔藓纤维突触似乎复制，在他们传达的信息方面，什么CA3细胞已经从内嗅皮层第二层细胞，项目都到齿状回和CA3。情景记忆的计算模型假设，苔藓纤维的功能是将一种新的、分离良好的活动模式强加给CA3细胞，以代表一种新的记忆，这种新的记忆胜过已经存储在CA3经常性侧支连接上的旧记忆的痕迹所产生的干扰。这一假设是否也适用于空间表征，正如最近对大鼠的神经生理学记录所描述的那样？为了定量地解决这个问题，我们估计DG的信息量可以传授一个新的CA3模式的空间活动，使用数学分析和计算机模拟的简化模型。我们确认，也在空间的情况下，所观察到的稀疏连接和活动水平是最合适的驱动内存存储，而不是启动检索。令人惊讶的是，该模型还表明，即使DG只对空间进行编码，它传递给CA3的大部分信息也会获得非空间和情节特征，类似于随机数生成器。这表明，需要进一步的海马处理，以充分利用DG输入的空间。
英文摘要：
In the mammalian hippocampus, the dentate gyrus (DG) is characterized by sparse and powerful unidirectional projections to CA3 pyramidal cells, the so-called mossy fibers. Mossy fiber synapses appear to duplicate, in terms of the information they convey, what CA3 cells already receive from entorhinal cortex layer II cells, which project both to the dentate gyrus and to CA3. Computational models of episodic memory have hypothesized that the function of the mossy fibers is to enforce a new, well separated pattern of activity onto CA3 cells, to represent a new memory, prevailing over the interference produced by the traces of older memories already stored on CA3 recurrent collateral connections. Can this hypothesis apply also to spatial representations, as described by recent neurophysiological recordings in rats? To address this issue quantitatively, we estimate the amount of information DG can impart on a new CA3 pattern of spatial activity, using both mathematical analysis and computer simulations of a simplified model. We confirm that, also in the spatial case, the observed sparse connectivity and level of activity are most appropriate for driving memory storage and not to initiate retrieval. Surprisingly, the model also indicates that even when DG codes just for space, much of the information it passes on to CA3 acquires a non-spatial and episodic character, akin to that of a random number generator. It is suggested that further hippocampal processing is required to make full spatial use of DG inputs.
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