Contribution of head-direction cells to path integration within grid cell networks

我们在日常活动中有效导航的能力取决于内侧内嗅皮层的神经元。在这个大脑区域内，网格细胞提供了我们位置的内部表征。当我们在空间中移动时，网格单元更新它们的位置估计值以反映我们每时每刻的位置，就像我们在行走时GPS设备中更新我们当前的位置一样。这个过程被称为路径整合，在网格单元的情况下，取决于我们的前进速度和行走速度的整合。当前网格细胞的计算模型认为，头部信息来自于另一种类型的神经元——头部方向细胞（HD）。每个HD细胞只有在动物的头部指向特定方向时才会被激活，不同的HD细胞有不同的偏好方向。尽管有大量的计算模型解释了网格单元的路径整合，但我们对路径整合的理解仍然不完整，至少有两个原因。首先，没有明确的实验证据表明HD细胞的活动控制路径整合的方向成分。其次，HD细胞群的异质性和复杂性被低估了。例如，所有的模型都假设HD细胞形成一个均匀的群体，但我们最近的实验表明情况并非如此。该研究项目的总体目标是调查HD细胞是否以及如何促进路径整合。我们将解决以下两个问题：1)网格细胞网络中路径整合的角度分量是否受到头部方向细胞活动的控制？2)所有内侧内嗅皮层HD细胞的偏好方向是否取决于丘脑区域HD细胞的输入？我们将通过同时记录HD细胞和网格细胞，并采用光遗传学技术来操纵主要的丘脑HD输入到皮层来回答这些问题。

Our ability to navigate efficiently during our daily activities depends on neurons of the medial entorhinal cortex. Within this brain area, grid cells provide an internal representation of our location. When we move in space, grid cells update their location estimate to reflect our moment-to-moment position, much like our current location is updated in a GPS device as we walk. This process is called path integration and, in the case of grid cells, depends on the integration of our heading and walking speed. Current computational models of gridcells propose that heading information comes from inputs from a second type of neurons called head-direction (HD) cells. Each HD cell is active only when the head of an animal points in a specific direction, with different HD cells having different preferred directions.Despite the abundance of computational models explaining path integration by grid cells, our understanding of path integration is still incomplete for at least two reasons. First, there is no clear experimental evidence that the activity of HD cell controls thedirectional component of path integration. Second, the level of heterogeneity and complexity within the HD cell population is underestimated. For example, all models assume that HD cells form a homogeneous population, but our recent experiments indicate that this is not the case. The general aim of this research project is toinvestigate whether and how HD cells contribute to path integration. We will address the following two questions: 1) Is the angular component of path integration in grid cell network controlled by the activity of head-direction cells? 2) Does the preferred direction of all HD cells in the medial entorhinal cortex depend on inputs from HD cells in thalamic areas? We will answer these questions by performing simultaneous recordings from HD cells and grid cells, and by employing optogenetic techniques to manipulate the main thalamic HD inputs to the cortex.