The hippocampus is critical for episodic memory. Although hippocampal activity represents place and other behaviorally relevant variables, it is unclear how it encodes numerous memories of specific events in life. To study episodic coding, we leveraged the specialized behavior of chickadees – food-caching birds that form memories at well-defined moments in time whenever they cache food for subsequent retrieval. Our recordings during caching revealed very sparse, transient barcode-like patterns of firing across hippocampal neurons. Each "barcode" uniquely represented a caching event and transiently reactivated during the retrieval of that specific cache. Barcodes co-occurred with the conventional activity of place cells, but were uncorrelated even for nearby cache locations that had similar place codes. We propose that animals recall episodic memories by reactivating hippocampal barcodes. Similarly to computer hash codes, these patterns assign unique identifiers to different events and could be a mechanism for rapid formation and storage of many non-interfering memories.

Funding provided by: New York Stem Cell FoundationROR ID: https://ror.org/03n2a3p06Award Number: Funding provided by: NIH Office of the DirectorROR ID: https://ror.org/00fj8a872Award Number: DP2-AG071918 Funding provided by: National Institute of HealthROR ID: https://ror.org/05h1kgg64Award Number: 5F32MH123015 Funding provided by: Simons FoundationROR ID: https://ror.org/01cmst727Award Number:

Raw electrophysiological, calcium imaging, and behavioral video recordings during food caching behavior in chickadee hippocampus were collected and pre-processed as described in the associated manuscript.