How Does the Brain Navigate in Space

Speaker: Edvard I. Moser (Kavli Institute for Systems Neuroscience, NTNU, Trondheim, Norway) Heller Lecture Series in Computational Neuroscience 22nd February, 2010 http://icnc.huji.ac.il/activities/hel... The ability to find one's way depends on the brain's ability to integrate information about location, direction and distance. This ability is present across a wide range of species and, in mammals, depends on a phylogenetically conserved set of brain structures, including the hippocampus and the entorhinal cortex. I will show that the medial entorhinal cortex is part of this network, containing a two-dimensional metric map of the animals changing location in the environment. A key component of this map is the grid cell. Grid cells fire selectively at regularly spaced positions in the environment such that, for each cell, activity is observed only when the animal is at places that together define a repeating triangular pattern tiling the entire environment covered by the animal, almost like the cross points of graph paper, but with an equilateral triangle as the unit of the grid. Grid cells are topographically arranged in the sense that neighbouring cells have grid frequency and grid orientation and that the scale of the grid increases along the dorsoventral axis of medial entorhinal cortex. In medial entorhinal cortex and pre- and parasubiculum, grid cells co-localize with other recently discovered entorhinal cell types such as head-direction cells, conjunctive grid × head direction cells, and border cells, which each contribute to representation of current location in moving animals. Position-related inputs from these cell types are coordinated with stored representations of the same environment in the hippocampus. I will show that the entorhinal-hippocampal map has strong innate components. A rudimentary map of space is present in entorhinal cortex and hippocampus when 2½-week old pre-weanling rats explore open environments outside the nest for the first time. The map contains prototypic head direction cells, place cells and grid cells. While the directional cells of the presubiculum have adult-like properties from the beginning, place cells and grid cells evolve more gradually towards regular and stable spatial firing patterns. The refinement of the early spatial component of the map is accompanied by an increase in network synchrony among neighbouring stellate cells in the medial entorhinal cortex. The presence of adult-like directional signals before navigational experience raises the possibility that inputs from directional cells are instrumental in setting up networks for grid and place representations in the developing entorhinal and hippocampal cortices.