Identification of rule for expression and selection of engram cells

The brain stores and recalls memories through a set of neurons, termed engram cells. 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.

本研究成果では、日々の生活で経験するエピソードの記憶について、脳内の神経細胞がどのような様式で集団で活動し記憶情報を符号化しているのかを明らかにしたとともに、経験に応じて形成された記憶が睡眠中に定着する様子を観察し明らかにした。これらの知見は、記憶の科学的かつ本質的な理解に貢献するものであり、脳内に表出した情報の解読法の提案や、効率の良い記憶学習法、認知症などの記憶障害の早期診断法への応用につながることが期待される。