Sequence learning and the role of the hippocampus in rodent navigation

The hippocampus has long been associated with navigation and spatial representations, but it has been difficult to link directly the neurophysiological correlates of hippocampal place cells with navigational planning and action. In recent years, large-scale population recordings of place cells have revealed that spatial sequences are stored and activated in ways that may support navigational strategies. Plasticity mechanisms allow the hippocampus to store learned sequences of locations that may allow predictions of future locations based on past experience. These sequences can also be activated during navigational behavior in ways that may allow the animal to learn trajectories toward goals. Task-dependent alterations in place cell firing patterns may reflect the operation of the hippocampus in associating locations with navigationally relevant decision variables.

► Task-dependent alterations of place cells may reflect a Markovian state space. ► Long-term storage of spatial sequences may be localized to the CA3 subregion. ► Theta sequences and place field expansion may reflect common mechanisms. ► Reverse replay of entire trajectories offers an efficient mode for route learning. ► Place cells may support navigation and generalization at multiple scales.