Researchers at the University of Michigan have developed a new theory on how our brains strengthen and organize memories during sleep. The theory suggests that non-REM (NREM) sleep grows and stabilizes memories, while REM sleep prunes overlapping or irrelevant ones, keeping them distinct.
The study found that reversing the NREM to REM sequence causes memory degradation, highlighting why this natural progression of sleep stages is so evolutionarily conserved. By combining mouse data with circuit-based simulations, researchers discovered how acetylcholine dynamics shape memory during sleep.
The theory proposes that memories are like shrubs, and non-REM sleep helps them grow taller and stronger, while REM sleep prunes any unnecessary branches to keep them distinct. The study also found that in humans, this sequence of events can help us remember everyday tasks better after a good night’s sleep.
While more research is needed, the findings offer a compelling explanation for how sleep architecture supports learning and memory. The researchers’ model suggests that cholinergic modulation plays a critical role in this process, with low acetylcholine levels during NREM sleep leading to network-wide disinhibition and bursts of synchronized activity, while high acetylcholine levels during REM sleep suppress firing in all but the most strongly recruited excitatory neurons.
The study’s lead author, Sara Aton, stated that the natural progression of sleep stages is crucial for memory consolidation. “It only works if you have this sequence,” she said. “If you go in reverse and have REM first, it prunes everything away.” The researchers’ findings have implications for our understanding of how sleep supports learning and memory, and suggest that targeting specific aspects of sleep may be a key to improving cognitive function.
Source: https://neurosciencenews.com/sleep-memory-sculpting-29316