Impact of temporal coding of presynaptic entorhinal cortex grid cells on the formation of hippocampal place fields.

Many behavioural experiments have pointed out the important role played by the hippocampus in spatial navigation. This role was enlightened by the discovery of hippocampal cells in rodents firing only at very specific locations in an environment, the so-called 'place field'. Recently, it has been observed that one synapse upstream of the hippocampus, entorhinal cells fire when the rat is located at any of the vertices of grid fields covering the environment. Furthermore, it was reported that both hippocampal and entorhinal cells have firing activity modulated by the theta local field potential in term of theta phase precession. In a previous report, the authors suggested that the temporal code driven by theta phase precession should play an important role in the building of hippocampal place cells from entorhinal grid cells. Here, with the help of a simpler computational model, we further investigate the implications of our hypothesis. We demonstrate that the nonlinear nature of the shape of the phase precession predicts that place field location are slightly backward shifted according to the direction of the rat.