Place field dynamics in retrosplenial cortex compared to hippocampus.

The encoding, storage, and updating of memories in cortical networks are poorly understood. In retrosplenial cortex (RSC), cells respond to the animal's position as it traverses a real or virtual (VR) linear track. Most position correlated cells (PCCs) in RSC require an intact hippocampus to form, but survive subsequent hippocampal damage. To examine whether RSC and hippocampal PCCs undergo remapping and spatial tuning development in parallel or sequentially, neuronal activity in RSC or CA1 was recorded using two-photon calcium imaging in mice running on VR tracks. RSC PCC activity underwent global remapping like CA1, with approximately the same dynamics of tuning development in the novel context. However, fields in RSC did not show place field expansion, in familiar or novel environments. Thus, while most properties of global remapping are shared between RSC and CA1, place field shift and expansion are notably restricted to hippocampus. Thus, our data suggests that RSC place specificity is either not 'inherited' directly from hippocampus or the hippocampal influence on RSC PCC formation may be restricted to hippocampal spikes occurring in the early phase of the theta rhythm (and thus late within the place field).