How does sleep help shape new memory networks?
The dual role of sleep in preserving past memories while preparing for future ones has been revealed.
Sleep is widely known to play an important role in memory processing and consolidation, yet whether or not sleep also plays a role in preparing the brain for new learning is unclear. Now, researchers from the University of Toyama (Japan), led by Kaoru Inokuchi, have investigated this, uncovering that these processes occur in parallel during sleep. This could open up new opportunities for cognitive enhancement and treating memory disorders.
Every day we have new experiences that form a myriad of memories that help to shape our personalities. These memories require formation, storage and retrieval, which rely on specialized groups of neurons in the hippocampus known as engram cells. Engram cells physically encode our memories and allow them to later be recalled.
While the role of engram cells in memory processing and allocation is well understood, their potential involvement and role in future learning is less clear. To tackle this, Inokuchi and the team used an advanced imaging system that combines live calcium imaging with engram cell labelling. This allowed them to track the activity of engram cells in mice before, during and after learning experiences, as well as during periods of sleep.
The neural activity underlying human conversation
The dynamic organization of neural activities underlying conversation has been revealed.
The team found that engram cells formed during learning showed reactivation patterns, suggesting prior activity during sleep before learning. During post-learning sleep, further periods of reactivation take place to consolidate and stabilize the new memory.
In parallel with consolidation, a separate population of neurons was found to become increasingly synchronized during post-learning sleep. This population was later found to encode new, different learning experiences, leading the team to coin them as engram-to-be cells. “Engram-to-be cells exhibited increased coactivity with existing engram cells during sleep, suggesting that this interaction helps shape new memory networks,” commented Inokuchi.
To further investigate this, the team developed an experimentally validated neural network model that simulated how engram-to-be cells might emerge. This model indicated that mechanisms that adjust connection strengths between neurons during sleep – synaptic depression and scaling – are key for developing and preparing engram-to-be cells. When depression and scaling processes were disabled, the preparation of engram-to-be cells was significantly impaired.
The results of this study help to further our understanding of memory and learning, highlighting the dual role that sleep plays in memory consolidation and preparing for future memories. This could open up new opportunities for cognitive enhancement and treating memory disorders. “We believe that manipulating brain activity during sleep or sleep patterns may uncover methods to enhance memory by unlocking the brain’s latent potential,” concluded Inokuchi.
