During this talk I will present some data showing how hippocampal spatial representations emerge and develop as rat pups first begin to explore their environment. We recorded the activity of CA1 pyramidal cells and medial entorhinal cortex neurons in pre-weanling rat pups. Adult-like directional firing is already present during initial exploration (at postnatal day 16). Place cell firing, although present, is initially less precise and stable, slowly maturing throughout juvenility. Grid cell firing appears later, around weaning (postnatal day 21), but matures rapidly to adult levels. Experience in the recording environment does not have an effect on the quality and stability of spatial representations. The early appearance of directional firing suggests that it might be innately specified, while the late emergence of grid firing suggests that the place cell network, at least during development, does not rely on grid signals to be set up.
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