Daytime Brain Wave Patterns May Explain How Memories Are Stored During Sleep

In a recent study, researchers at the NYU Grossman School of Medicine proposed a mechanism to explain how the brain chooses which memories to keep.

Sharp-Wave Ripples

During the day, the brain undergoes flashes of intense activity after new events. Called “sharp-wave ripples” for the shape they take on a graph, these brain waves represent brain cells firing in different patterns depending on the event.

In the new study, published in March in the journal Science, researchers hypothesized that sharp-wave ripples generated while awake may serve as a kind of bookmark to tag events that are worth remembering.

The study found that important events seem to provoke a higher number of sharp-wave ripples. Guided by this cue, during the next sleep period, the brain knows to go back to those specific patterns and repeat them many more times, effectively engraving those experiences into long-term memory.

A Maze of Data

To test their theory, the researchers ran maze tests on mice. First, they figured out how to identify brain wave data that lined up with the physical attributes of different maze sections. This allowed them to match brain wave patterns to specific trials as mice navigated the maze. 

Next, the research team identified condensed versions of these patterns in sharp-wave ripples immediately following the trial. Comparing the data with brain activity during sleep, the team was able to confirm that when a pattern appeared more in the immediate period after a trial, it also appeared more during the next sleep period.

Bookmarks in the Brain

According to the study authors, the more sharp-wave ripples occur after an event, the more likely the pattern will be repeated during sleep and the better the event will be remembered. By contrast, failure to replay a pattern during sleep means that the corresponding events will likely be forgotten. The brain’s memory center is also more likely to flag experiences that are new, rewarding, or that occur multiple times.

In a press release, senior study author György Buzsáki, Ph.D., explained, “Our study finds that sharp wave-ripples are the physiological mechanism used by the brain to ‘decide’ what to keep and what to discard.” 

Memory consolidation during sleep is a highly complex process Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source that involves different sleep stages and brain wave patterns. However, this discovery of the link between sharp-wave ripples produced while awake and while asleep helps complete part of the puzzle — and reinforces the importance of quality sleep for staying mentally sharp. Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source  

Future studies in humans could build on these results. Says the study’s first author Wannan “Winnie” Yang, Ph.D., “Future research may reveal devices or therapies that can adjust sharp wave-ripples to improve memory, or even lessen recall of traumatic events.”