Development of the Spatial Representation System in the Rat

TLDR

The adult hippocampal‑parahippocampal circuit encodes space and orientation via head‑direction, place, and grid cells, and early adult‑like directional signals may help establish place and grid networks. Rudimentary spatial maps appear in 2½‑week‑old rat pups, with adult‑like head‑direction cells present from the start, while place and grid cells develop more slowly—grid cells being the slowest—and this refinement is accompanied by rising synchrony among entorhinal stellate cells.

Abstract

In the adult brain, space and orientation are represented by an elaborate hippocampal-parahippocampal circuit consisting of head-direction cells, place cells, and grid cells. We report that a rudimentary map of space is already present when 2 1/2-week-old rat pups explore an open environment outside the nest for the first time. Head-direction cells in the pre- and parasubiculum have adultlike properties from the beginning. Place and grid cells are also present but evolve more gradually. Grid cells show the slowest development. The gradual refinement of the spatial representation is accompanied by an increase in network synchrony among entorhinal stellate cells. The presence of adultlike directional signals at the onset of navigation raises the possibility that such signals are instrumental in setting up networks for place and grid representation.