Sleep Prepares the Brain for Future Memories, Study Finds

Your brain must do more than preserve an enormous store of memories already formed; it also needs to monitor fresh information every day. That means preparing to handle new memories before they happen, even as earlier ones are being processed.

Sleep is widely recognised as essential to memory and learning, among its other benefits, although scientists are still unpicking many of the exact mechanisms behind it.

Conventionally, memory has been understood as a process that looks backwards: we undergo an experience, its memory is processed and retained during the following nights of sleep, and we are then able to retrieve it later when needed.

A new study, however, indicates that sleep may assist the brain with future memories as well as past ones. Alongside consolidating and preserving memories during sleep, the findings suggest that our brains are actively getting us ready to record events that have yet to take place.

How sleep supports memory formation

Memory is a wide-ranging, complex phenomenon that contributes to making us who we are. From a personal viewpoint, it can appear almost magical, as though it exists beyond separate physical parts.

Yet that is not the case. At the cellular level, clusters of specialised neurons called engram cells physically encode experiences from our lives in a form that can later be recalled.

Earlier research has firmly established that sleep is vital for this system to function correctly, though many of its physiological details are still uncertain. Beyond simply keeping memories, the brain carries out remarkable processing and organisational work, much of it during periods of mental rest.

In the new study, researchers in Japan aimed to understand more about sleep's part in processing memories, including how it prepares the brain for memorable experiences that have not occurred yet.

They used an imaging system in freely moving mice that could identify both engram and non-engram cells throughout the stages of memory processing. This allowed them to follow neuronal activity before, throughout and after the memorable events experienced by the mice.

The approach offered fresh insight into how distinct neuron populations behave under a range of cognitive conditions, including when mice slept before and after learning experiences.

Engram-to-be cells and future memories

The findings identified two simultaneous processes during sleep after learning. Firstly, engram cells that had originally encoded a memory displayed expected patterns of reactivation, part of the brain's well-established method of consolidating memories during sleep.

The research also uncovered a second notable group of neurons that were not yet linked to particular memories. These “engram-to-be cells”, as the researchers describe them, became progressively more synchronised while the mice slept after learning. The same groups of neurons subsequently encoded new and different memories.

“Engram-to-be cells exhibited increased coactivity with existing engram cells during sleep, suggesting that this interaction helps shape new memory networks,” says co-author Kaoru Inokuchi, a professor of biochemistry at the University of Toyama in Japan.

To shed further light on the processes involved, the team also created a neural network model that simulated activity in the hippocampus.

The model suggested that synaptic depression and scaling-processes known to alter neuronal connections during sleep-are probably important in arranging these engram-to-be cells. In the model, this function weakened when those mechanisms were switched off.

Engram cells and engram-to-be cells displayed compelling co-activation during sleep following learning, according to the study. This implies some level of coordination, or perhaps even information transfer, between neural networks involved in previous and forthcoming memories.

Why sleep quality may matter for learning

This indicates that sleep quality between learning events could affect not only how well we retain what we have already learnt, but also how effectively we remember new information in the near future.

Although further research is required, the findings could offer useful insight for education and the treatment of memory disorders. They may also help reveal new approaches for enabling people to maximise their cognitive performance.

“We believe that manipulating brain activity during sleep or sleep patterns may uncover methods to enhance memory by unlocking the brain's latent potential,” Inokuchi says.

Most importantly, though, the results add to the substantial body of existing evidence that everyone should treat sleep seriously.

“We want people to understand that sleep is not just about rest – it plays a crucial role in how the brain processes information,” Inokuchi says. “With that in mind, we hope everyone will begin to value sleep more and use it as a way to improve their overall quality of life.”

The study was published in Nature Communications.