By boosting specific brain waves during sleep, Cornell scientists helped mice hold on to memories that would normally fade within hours. The work could guide new approaches to treating Alzheimer’s disease and other forms of dementia.
Gently nudging the brain while it sleeps may help fragile memories stick around, according to new research in mice that could open doors for future dementia treatments.
Cornell University scientists report that by precisely stimulating the brain at night, they helped mice remember brief experiences that would normally be forgotten within hours. The research, published in the journal Neuron, focuses on a key memory process that is shared across mammals, including humans.
The team zeroed in on a particular pattern of brain activity called large sharp-wave ripples. These ripples are very short bursts of coordinated electrical activity, lasting about a tenth of a second, that occur in the hippocampus — a brain region crucial for forming new memories — and then spread to the neocortex, where long-term memories are stored more permanently.
The researchers found that these ripples act like a signal that a new experience is being transferred from short-term to long-term storage. When the ripples were strong and frequent during sleep, mice were more likely to remember what they had just experienced. When the ripples were weak or rare, the memory faded.
“This study advance our understanding of memory processing in the brain,” co-senior author Azahara Oliva, an assistant professor of neurobiology and behavior in Cornell’s College of Arts and Sciences, said in a news release.
To explore this process, the researchers recorded the activity of neurons in both the hippocampus and the neocortex while mice slept. They identified large sharp-wave ripples in the hippocampus that appeared during sleep and then propagated to the neocortex, marking moments when memories were being consolidated.
“Ripples are mediating the transfer of memory from the initial encoding in the hippocampus to long-term stable storage in the neocortex,” added co-senior author Antonio Fernandez-Ruiz, an assistant professor and Nancy and Peter Meinig Family Investigator in the Life Sciences in Cornell’s College of Arts and Sciences.
Next, the team asked a bold question: If these ripples help lock in memories, could boosting them rescue memories that would otherwise be lost?
To test this, they used optogenetics, a cutting-edge technique that allows scientists to control specific neurons with light. By implanting a tiny optical fiber in the brain, they could shine light at precise moments during sleep to activate neurons and strengthen the sharp-wave ripples.
In one experiment, mice were allowed to explore a new toy for just five minutes — a very brief encounter. When the researchers tested the animals four hours later, the mice typically did not remember the object, suggesting that the memory had not been consolidated.
But when the scientists used optogenetics to enhance the ripples associated with that experience during the mice’s subsequent sleep, the outcome changed. The same mice now behaved as if they remembered the toy, indicating that the boosted ripples had helped convert the fleeting experience into a more stable memory.
The approach was even effective in mice that had been engineered to have cognitive deficits, mimicking some aspects of human memory disorders.
“We were able to extend this memory consolidation in a condition where animals are unable to remember without our help,” Fernandez-Ruiz added.
That finding is especially important for Alzheimer’s disease and other forms of dementia, where the brain’s ability to consolidate new memories is disrupted. While the current work was done in mice, the basic architecture of memory — with the hippocampus encoding new experiences and the neocortex storing them long term — is similar in humans.
The study suggests that monitoring and potentially enhancing specific brain rhythms during sleep could one day become a strategy to support memory in people with cognitive decline. It also highlights sleep itself as a critical window for intervention, rather than focusing only on what happens while people are awake and learning.
As a next step, the Cornell team plans to apply the same nighttime manipulations in mice engineered to more closely mimic Alzheimer’s disease. By seeing whether boosting sharp-wave ripples can improve memory in these models, they hope to better understand how memory consolidation breaks down in dementia — and how it might be restored.
For now, the findings underscore a powerful idea: even memories that seem too fragile to last may be saved if the brain’s nighttime rhythms can be tuned just right.
Source: Cornell University