Summary: A new study shows that precisely manipulating brain activity during sleep can help mice retain memories that would normally fade, offering a potential pathway for treating memory loss conditions. Researchers identified a specific sleep-related pattern—large sharp-wave ripples—that signals when new experiences are being transferred from the hippocampus to the neocortex for long-term storage.
By boosting these ripples at just the right moment using optogenetics, scientists enabled mice to remember brief encounters they would typically forget. Even mice engineered with cognitive impairments displayed restored memory consolidation.
Because sleep-dependent memory mechanisms are highly conserved across mammals, the findings may open new doors for addressing memory decline in conditions like Alzheimer’s disease.
Key Facts
- Sleep Ripples Drive Memory: Large sharp-wave ripples during sleep act as markers of new experiences being transferred into long-term storage.
- Optogenetics Enhanced Recall: Stimulating neurons at ripple peaks allowed mice to remember events that would otherwise be forgotten.
- Therapeutic Potential: The approach restored memory consolidation in cognitively impaired mice, highlighting relevance to dementia research.
Source: Cornell University
Manipulating mouse brains during sleep improved their ability to remember new experiences that would normally be forgotten – a finding with important implications for treating Alzheimer’s disease and other forms of dementia that act on similar processes.
The study published in Neuron, is relevant to humans as the basic mechanisms of memory formation are very similar across mammals.
By selectively manipulating brain activity at specific times during sleep, the scientists found the mice remembered new experiences that were otherwise too brief for them to retain.
The researchers identified large sharp-wave ripples, a subset of brain activity patterns around 100 milliseconds long that is involved in consolidating and transferring new experiences from the hippocampus to the neocortex, where they are more permanently stored. The large sharp-wave ripples can now help researchers identify when new experiences are being converted to long-term memory.
“This study advance our understanding of memory processing in the brain,” said Azahara Oliva, assistant professor of neurobiology and behavior. Oliva is a senior author of the study along with assistant professor Antonio Fernandez-Ruiz.
In the study, Fernandez-Ruiz and Oliva recorded neuron activity in the hippocampus and neocortex. They identified large sharp-wave ripples in the hippocampus, which occur during sleep, and are then propagated to the neocortex.
“Ripples are mediating the transfer of memory from the initial encoding in the hippocampus to long-term stable storage in the neocortex,” Fernandez-Ruiz said.
The researchers observed that when an animal doesn’t remember an experience, large sharp-wave ripples were weak during sleep, but when it does remember, there were many of these ripple events.
Once the researchers identified this pattern, they used an advanced technique called optogenetics to shine a light in the brain with an optic fiber that then selectively activated neurons.
Optogenetics allowed the team to stimulate neurons at precise times to boost large sharp-wave ripples, which then consolidated a memory of an event the animal experienced right before sleep.
The team exposed mice to a new toy for five minutes and tested four hours later and found the animals didn’t remember. They then boosted ripples associated with that experience during sleep, and they found the mouse then did remember the object. The technique even worked in mice engineered to have cognitive deficits.
“We were able to extend this memory consolidation in a condition where animals are unable to remeber without our help,” Fernandez-Ruiz said.
This has important implications for better understanding Alzheimer’s disease, as these memory consolidation processes are also impaired in humans. In next steps, the researchers will apply the same manipulations in mice engineered to exhibit conditions similar to Alzheimer’s disease.
Key Questions Answered:
A: Large sharp-wave ripples—brief bursts of coordinated neural activity—signal the conversion of new experiences into long-term memories.
A: By timing optogenetic stimulation to coincide with these ripples, they boosted memory consolidation during sleep.
A: Memory consolidation is disrupted in disorders like Alzheimer’s, and enhancing these sleep-based processes could guide future treatments.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this sleep and memory research news
Author: Becka Bowyer
Source: Cornell University
Contact: Becka Bowyer – Cornell University
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Large sharp-wave ripples promote hippocampo-cortical memory reactivation and consolidation during sleep” by Antonio Fernandez-Ruiz et al. Neuron
Abstract
Large sharp-wave ripples promote hippocampo-cortical memory reactivation and consolidation during sleep
During sleep, ensemble activity patterns encoding recent experiences are reactivated in the hippocampus and cortex.
This reactivation is coordinated by hippocampal sharp-wave ripples (SWRs) and is believed to support the early stages of memory consolidation.
However, only a minority of sleep SWRs are associated with memory reactivation in the hippocampus and its downstream areas. Whether that subset of SWRs has specific physiological characteristics and directly contributes to memory performance is not known.
We identified a specific subset of large SWRs linked to memory reactivation in both the hippocampus and prefrontal cortex (PFC) of mice, and found that their occurrence selectively increased during sleep following new learning.
Closed-loop optogenetic SWR boosting during sleep was sufficient to enhance ensemble memory reactivation in the hippocampus and PFC.
This manipulation also improved subsequent memory retrieval and hippocampal-PFC coordination during waking, causally linking both phenomena to SWR-associated ensemble reactivation during sleep.
