Distinct roles of dentate gyrus and medial entorhinal cortex inputs for phase precession and temporal correlations in hippocampal CA3 place cells

The hippocampal CA3 subregion is a densely connected recurrent circuit that supports memory consolidation and retrieval by generating and storing sequential neuronal activity patterns that reflect recent experience. While theta phase precession is thought to be critical for generating sequential activity during memory encoding, the circuit mechanisms that support this computation across hippocampal subregions are unknown. By analyzing CA3 network activity in the absence of each of its theta modulated excitatory inputs, we show necessary and unique contributions of the dentate gyrus (DG) and the medial entorhinal cortex (MEC) to phase precession. DG inputs are essential for generating the preferential spiking of CA3 cells during late theta phases and for organizing the temporal order of neuronal firing, while MEC inputs modulate the general precision of phase precession. A computational model that accounts for the empirical findings suggests that DG inputs affect the phase and MEC inputs affect the amplitude of inhibitory subnetworks. Our results thus identify a novel and unique functional role of the DG for the generation of sequence coding in the CA3 recurrent circuit.