Phase precession: a neural code underlying episodic memory?

- Phase precession and theta sequences are hallmarks of hippocampal dynamics.
- Phase precession may enable sequence learning via a temporal compression.
- The mechanisms underlying phase precession are not well understood.
- Understanding phase-precession is essential to test its role in episodic memory.

In the hippocampal formation, the sequential activation of place-specific cells represents a conceptual model for the spatio-temporal events that assemble episodic memories. The imprinting of behavioral sequences in hippocampal networks might be achieved via spike-timing-dependent plasticity and phase precession of the spiking activity of neurons. It is unclear, however, whether phase precession plays an active role by enabling sequence learning via synaptic plasticity or whether phase precession passively reflects retrieval dynamics. Here we examine these possibilities in the context of potential mechanisms generating phase precession. Knowledge of these mechanisms would allow to selectively alter phase precession and test its role in episodic memory. We finally review the few successful approaches to degrade phase precession and the resulting impact on behavior.