Reconceiving the hippocampal map as a topological template.
Reconceiving the hippocampal map as a topological template.
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DOI：
10.7554/elife.03476
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发表时间：
2014-08-20
期刊：
影响因子：
7.7
通讯作者：
Frank LM
中科院分区：
文献类型：
--
作者：
Dabaghian Y;Brandt VL;Frank LM
海马在空间认知中的作用是无可争议的，但也存在争议。最初被认为是位置指定器的位置细胞，对各种刺激的反应是混杂的。在这里，我们测试的想法，我们最近在一个计算模型中证明，海马位置细胞可能最终感兴趣的空间的拓扑质量（其连接性）比它的几何形状（距离和角度），这种高阶功能将更符合其他已知的海马功能。我们记录了大鼠的位置细胞活动，探索变形的线性轨道，使我们能够从其拓扑结构中分离出轨道的几何形状。由此产生的地方字段保存的相对顺序访问的地方沿着的轨道，但不改变的韵律特征的轨道或方向的大鼠的运动。这些结果表明了对以前研究的重新解释和未来实验的新方向。http://dx.doi.org/10.7554/eLife.03476.001海马体是大脑中最容易识别的结构之一，因为它具有海马状的特征。20世纪90年代的脑成像研究表明，伦敦出租车司机的海马体比其他人大，这表明它在空间导航中发挥作用。这与之前在啮齿类动物身上的发现是一致的，之前的研究表明，当动物通过迷宫时，海马体是活跃的。电极记录显示，每当动物处于特定环境的特定位置时（例如，在一个有白色墙的小房间的左后角），海马体中的一个或少数细胞就会对该位置进行编码。当动物在同一环境中移动到一个新的位置时，其他细胞将被激发来编码新的位置。通过这种方式，这些细胞（也就是所谓的位置细胞）可以共同构建一个虚拟的环境“地图”。一般认为，海马地图以绝对距离和位置之间的角度来表示空间，就像街道地图一样。然而，这种类型的几何映射似乎与某些实验的结果不一致。Dabaghian等人提出，海马地图是基于拓扑结构，或位置的相对顺序和它们之间的连接，而不是像地铁地图。随后，计算机模型表明，虚拟模拟的位置细胞可以有效地“学习”不同环境的拓扑特征。现在，Dabaghian等人提供了他们自己的经验数据，通过记录大鼠海马中位置细胞的电脉冲，支持海马“地铁式”地图的存在，因为动物跑过U形迷宫。迷宫的结构是这样的，它的臂可以是直的，也可以折叠成三角形。以这种方式改变迷宫并不会改变其拓扑结构，因为它的各个组件的相对顺序（如臂中食物威尔斯的位置）是不变的，但它确实改变了迷宫的几何形状。值得注意的是，当老鼠穿过迷宫的不同构造时，它们前丘中位置细胞的活动基本保持不变，这与基于拓扑结构而不是几何结构的地图相一致。Dabaghian等人的工作提供了海马地图与地铁地图比街道地图更相似的证据，为先前具有挑战性的结果提供了解释，并为海马记忆功能的进一步实验提供了框架。DOI：http://dx.doi.org/10.7554/eLife.03476.002网站
The role of the hippocampus in spatial cognition is incontrovertible yet controversial. Place cells, initially thought to be location-specifiers, turn out to respond promiscuously to a wide range of stimuli. Here we test the idea, which we have recently demonstrated in a computational model, that the hippocampal place cells may ultimately be interested in a space's topological qualities (its connectivity) more than its geometry (distances and angles); such higher-order functioning would be more consistent with other known hippocampal functions. We recorded place cell activity in rats exploring morphing linear tracks that allowed us to dissociate the geometry of the track from its topology. The resulting place fields preserved the relative sequence of places visited along the track but did not vary with the metrical features of the track or the direction of the rat's movement. These results suggest a reinterpretation of previous studies and new directions for future experiments. DOI: http://dx.doi.org/10.7554/eLife.03476.001 The hippocampus is one of the most easily recognizable structures in the brain owing to its characteristic seahorse-like shape. Brain imaging studies in the 1990s famously showed the hippocampus to be larger in London taxi drivers than in other people, suggesting that it plays a role in spatial navigation. This was consistent with previous findings in rodents, which had shown that the hippocampus is active when animals find their way through mazes. Electrode recordings have revealed that whenever an animal is in a specific location of a particular environment (for example, in the back left-hand corner of a small room with white walls) one or a small number of cells within the hippocampus will fire to encode that location. When the animal moves to a new location within the same environment, other cells will fire to encode the new location. In this way, the population of cells—which are known as place cells—can together construct a virtual ‘map’ of the environment. It is generally assumed that this hippocampal map represents space in terms of the absolute distances and angles between locations, rather like a street map. However, this type of geometric map appears inconsistent with the results of certain experiments. Dabaghian et al. proposed instead that the hippocampal map is based on topology, or the relative order of locations and the connections between them, rather like a subway map. Subsequently, computer models demonstrated that virtual simulations of place cells could effectively ‘learn’ the topological features of different environments. Now, Dabaghian et al. provide their own empirical data to support the existence of a hippocampal ‘subway-style’ map by recording the electrical impulses from place cells in the rat hippocampus as the animals ran through a U-shaped maze. The maze was constructed so that its arms could either be straight or folded into zigzags. Changing the maze in this way does not alter its topology because the relative order of its various components—such as the positions of food wells in the arms—is unchanged, but it does alter the maze's geometry. Notably, as rats ran through different conformations of the maze, the activity of the place cells in their hippocampi remained largely unchanged, consistent with a map based on topology rather than geometry. By providing evidence that hippocampal maps have more in common with subway maps than street maps, the work of Dabaghian et al. offers an explanation for previously challenging results and provides a framework for further experiments into hippocampal memory function. DOI: http://dx.doi.org/10.7554/eLife.03476.002