A Universal Sleep Pattern May Enhance Memory Formation and Separation

Sleep plays a vital role in our physical and mental well-being, yet its full biological purpose remains partially understood. Recent research from the University of Michigan offers a compelling hypothesis about the fundamental structure of sleep cycles. Scientists have observed that all sleeping organisms follow a similar repeating pattern consisting of non-REM (rapid eye movement) and REM sleep stages. During non-REM sleep, brain activity is subdued, facilitating memory consolidation. Subsequently, REM sleep involves heightened brain activity and eye movements, believed to help process and fine-tune memories.

Sara Aton, a professor at U-M, emphasizes the evolutionary significance of this universal sleep cycle. "The consistent and non-reversible sequence suggests a deep biological importance," she notes. Despite extensive study, the core function of this pattern has been elusive.

Building on experimental data from mice and computational brain modeling, researchers led by Aton and Michal Zochowski proposed a novel hypothesis. They suggest that non-REM sleep promotes the growth and strengthening of memories, akin to cultivating shrubs. REM sleep then acts as a pruning phase, refining memories by removing overlap and preventing confusion between related memories.

The sequence is crucial—if REM sleep occurs before non-REM, it can erode memories instead of reinforcing them. When applied correctly, this cycle enhances memory retention and segregation, helping the brain preserve distinct memories efficiently.

This theory is supported by experiments where mice underwent conditioning tests, revealing how sleep stages influence memory retention. In humans, this understanding could explain everyday experiences, such as better recall of meetings or events following a good night’s sleep. During non-REM sleep, memories are strengthened, while REM sleep helps keep these memories distinct by preventing them from merging.

The study involved monitoring hippocampal activity in mice after exposing them to new environments and shocks. While current techniques limit the ability to record individual neuron activity precisely during sleep, the researchers employed computational models that simulate neural circuitry. These models, considering factors like acetylcholine levels, offered insights into how sleep regulates memory processing.

Although promising, the researchers acknowledge that their simplified models and basic experiments leave room for further refinement. Future studies will aim to test the hypothesis with more complex memory scenarios and advanced neural recording methods, ultimately aiming to confirm how this sleep pattern benefits memory functions.

This research underscores the importance of maintaining proper sleep cycles for cognitive health and could lead to new strategies for improving memory and learning across species.