Elsevier

Current Opinion in Neurobiology

Volume 43, April 2017, Pages 130-138
Current Opinion in Neurobiology

Phase precession: a neural code underlying episodic memory?

https://doi.org/10.1016/j.conb.2017.02.006Get rights and content

Highlights

  • •

    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.

Section snippets

What are the possible functions of phase precession?

Phase precession has typically been studied in the rodent hippocampal formation while the animal navigates in a one-dimensional or two-dimensional environment [9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19•, 20], but phase precession has also been observed outside the hippocampal formation [21], and in a variety of contexts including running on a wheel [3] or treadmill [22], jumping [23], virtual reality [24•, 25•, 26•], and during fixation [27]. Recent evidence indicates phase precession also in

Interfering with phase precession

Although there is no consensus on the mechanisms generating phase precession, it has been possible to alter the entorhinal-hippocampal circuitry in specific ways that resulted in abnormal phase precession. Robbe and Buzsáki [76] examined the effect of cannabinoids on the spatial coding properties of place cells in the hippocampus, as well as on memory and navigation in a spatial-alternation task: the administration of a cannabinoid agonist impaired rats in performing the delayed

Concluding remarks

The study of phase precession has shed light on hippocampal dynamics, on memory-related and goal-related behaviors, and on the computational roles of oscillations in cognition [78]. Whether phase precession enables sequence learning, is a signature of a retrieval process, or neither, remains an open question.

Overall, to unravel functional roles of phase precession, it should be studied in the context of hippocampus-dependent tasks (e.g. [3, 42••, 70••]) that allow for the isolation of internal

Conflict of interest statement

Nothing declared.

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

  • • of special interest

  • •• of outstanding interest

Acknowledgements

We thank Eric Reifenstein and Tiziano D’Albis for comments on the manuscript.

This work was supported by the Deutsche Forschungsgemeinschaft (DFG) [grant numbers GRK 1589/2, KE 788/3-1] and the Bundesministerium für Bildung und Forschung (BMBF) [grant numbers 01GQ1001A, 01GQ0972].

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    Present address: Center for Neural Science, New York University, 4 Washington Place, New York, NY, USA.

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