Previous research examining the relationship between sleep and memory has revealed that memories are consolidated during post-experience sleep through the reactivation of neural cell populations called "engram cell populations" that are responsible for memory. A research team led by Distinguished Professor Kaoru Inokuchi at the Faculty of Medicine, Academic Research Division, the University of Toyama, used their proprietary technology to observe neural cell activity with light. They observed in mice brains how cell populations in the hippocampus, the brain region responsible for memory, behave during the experience of new events and during sleep before and after these experiences. The study revealed that two processes occur simultaneously during sleep: the consolidation of past memories and preparation for acquiring future memories.
The research team placed mice in a new space A for exploration, then the following day, after the mice woke from sleep, they had them re-experience space A before exploring a new space B. The team examined how cell populations in the hippocampus behaved during sleep before and after these experiences. They discovered that engram cell populations responsible for future experience memories were already prepared in the brain during sleep before those experiences occurred. Furthermore, they found that these cell populations appeared during sleep after recording previous experiences and were active simultaneously with the engram cell populations of those previous memories.
The team then conducted simulations using neural circuit models. They demonstrated that for engram populations to emerge, synaptic changes during sleep in cells other than the previous memory's engram cells, influenced by the reactivation of those engram cells, are crucial. By clarifying how the brain systematically acquires daily memories during sleep, this discovery raises expectations that interventions in brain activity during sleep or sleep methods could better harness the brain's potential abilities, leading to methods for improving memory.
(TEXT: Masanori Nakajo)
