Orchestrated ensemble activities constitute a hippocampal memory engram

Khaled Ghandour, Noriaki Ohkawa, Chi Chung Alan Fung, Hirotaka Asai, Yoshito Saitoh, Takashi Takekawa, Reiko Okubo-Suzuki, Shingo Soya, Hirofumi Nishizono, Mina Matsuo, Makoto Osanai, Masaaki Sato, Masamichi Ohkura, Junichi Nakai, Yasunori Hayashi, Takeshi Sakurai, Takashi Kitamura, Tomoki Fukai, Kaoru Inokuchi

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


The brain stores and recalls memories through a set of neurons, termed engram cells. However, it is unclear how these cells are organized to constitute a corresponding memory trace. We established a unique imaging system that combines Ca2+ imaging and engram identification to extract the characteristics of engram activity by visualizing and discriminating between engram and non-engram cells. Here, we show that engram cells detected in the hippocampus display higher repetitive activity than non-engram cells during novel context learning. The total activity pattern of the engram cells during learning is stable across post-learning memory processing. Within a single engram population, we detected several sub-ensembles composed of neurons collectively activated during learning. Some sub-ensembles preferentially reappear during post-learning sleep, and these replayed sub-ensembles are more likely to be reactivated during retrieval. These results indicate that sub-ensembles represent distinct pieces of information, which are then orchestrated to constitute an entire memory.

Original languageEnglish (US)
Article number2637
JournalNature communications
Issue number1
StatePublished - Dec 1 2019

ASJC Scopus subject areas

  • Chemistry(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Physics and Astronomy(all)


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