Why do we remember certain moments while forgetting others? Every day, our minds are bombarded with thousands of pieces of information, yet our brains have a limited capacity to consolidate these experiences into lasting memories. This means we need a way to hold on to what is most important, and disregard irrelevant details.
Now researchers at the University of York have uncovered the neural mechanism that instructs the brain which daily experiences to save as long-term memories during sleep.
In the study, published in the journal PLOS Biology, researchers analysed brainwave activity while participants were learning new associations between words and pictures. It is already known that after learning, sleep plays a central role in strengthening new learning into long-term memories.
The researchers discovered that during learning, the brain "tags" certain memories for processing during later sleep. This tagging provides a way for the sleeping brain to strengthen only what is deemed important to remember.
This tagging was linked to a specific brainwave pattern known as a "theta rhythm" present during learning. The strength of these theta rhythms provided an instructional cue to help organise brain activity during sleep.
Those memories with a particularly strong theta rhythm at learning were preferentially strengthened during sleep, ultimately leading to better memory recall, the scientists said.
They say the findings show that the brain prioritises and strengthens important information by using specific neural signals during learning that guide memory strengthening processes during sleep. Determining what our brains decide to strengthen during sleep could help better understand why some individuals are vulnerable to conditions such as depression.
Lead author Dr Dan Denis , from the Department of Psychology at the University of York, said: "It has long been known that a good night's sleep is important for processing memories.
"How the brain decides what is important to remember and what can be forgotten is still a mystery. These new findings help to answer that question, by uncovering for the first time a signature of neural activity which instructs the brain which experiences to process during sleep and form into long-term memories."
"If we remembered everything that we experienced, our brains would quickly reach system overload. By selectively prioritising important events in our lives, be they emotionally salient or important for the future, we are able to use our past experiences to help guide our interactions in the world."
The researchers note that while selective memory consolidation is vital for daily functioning, disruptions to this filtering process could play a role in psychiatric conditions.
Dr Denis added: "Although it is typically adaptive to prioritise certain kinds of information, there are cases where this becomes maladaptive. For example, in depression, individuals tend to overallocate attentional resources to negative information, whilst disregarding or downplaying more positive experiences.
"Our new findings shed new light on the brain processes that dictate what is ultimately remembered, and may open new avenues for understanding and treating common mental health problems such as depression."
