How Memory Retention Survives Hibernation in Mice

What Is Memory Retention and Why Is It So Difficult to Explain?

Memory retention refers to the brain's ability to preserve previously learned information and retrieve it later. Scientists have long suspected that memories are partly represented by physical changes in the connections between neurons.

These connections are called synapses. When people or animals learn something new, changes in synaptic strength and structure can help encode that experience. But there is a major problem with this explanation: synapses are not permanent.

The brain continuously remodels itself. Connections can become stronger, weaker, disappear, or form again. This raises an important question: if the physical connections supporting a memory are constantly changing, how can the memory remain stable for years?

A new study published in Science on August 13, 2026, provides an unusual clue. Researchers used an artificial hibernation model in mice to create an extreme example of brain remodeling. The animals experienced a major reduction in neuronal activity and lost more than half of their hippocampal synapses. Yet their previously learned memories remained intact.

How Hibernation Changes the Brain

Hibernation is an extraordinary physiological state. During torpor, animals can dramatically reduce their body temperature, metabolism, and neural activity.

Previous research has already shown that hibernation can produce substantial structural changes in the hippocampus, a brain region strongly associated with learning and memory. Studies of ground squirrels, for example, have documented reversible changes in dendritic spines and synaptic structures during hibernation.

The new research took this phenomenon a step further by using mice placed into an artificially induced hibernation-like state.

The researchers examined the animals' hippocampi before, during, and after this state. Neuronal activity dropped by approximately 70%, while more than half of the synapses were eliminated.

Under traditional theories of memory storage, such extensive synaptic loss might be expected to severely disrupt previously formed memories.

But that is not what happened.

Memory Retention Survives Major Synapse Loss

The mice had previously learned tasks involving locations associated with food rewards and contextual fear. After emerging from the artificial hibernation state, the animals were tested again.

Despite the enormous structural changes in their brains, they could still remember what they had learned.

This result is important because it suggests that memory retention does not necessarily require every individual synaptic connection involved in a memory to remain intact.

Instead, the researchers found evidence that the brain may preserve something more complex: the architecture of groups of memory-related connections.

The study found that some synapses belonging to memory-encoding neurons were organized into spatial clusters. These clusters were preferentially preserved during the hibernation-induced remodeling.

In other words, the brain may not need to protect every single "memory connection." It may instead protect the broader pattern in which those connections are organized.

“Synaptic engram architecture, rather than larger spines per se, is resilient to network remodeling and associated with long-term memory retention.”

This finding could represent an important shift in how scientists think about the physical basis of memory.

The Surprising Role of Multisynaptic Boutons

One of the most interesting discoveries involved structures known as multisynaptic boutons.

Normally, a presynaptic terminal sends signals to a postsynaptic dendritic spine. A multisynaptic bouton is different because a single presynaptic terminal can form connections with multiple dendritic spines.

Researchers found that memory-related synapses that survived hibernation were frequently associated with these structures.

This may provide the brain with a form of structural redundancy or organization. Instead of depending on one isolated connection, multiple memory-related connections may be linked through a shared neural structure.

The researchers reported that only around 3.3% of randomly selected synapses in non-hibernating mice were associated with multisynaptic boutons, highlighting how unusual these structures are in the broader population of synapses.

The findings do not yet prove that multisynaptic boutons directly cause memory preservation. Rather, they reveal a strong association between this architecture and memories that survive extensive neural remodeling.

That distinction matters.

The researchers themselves emphasize that the current evidence does not establish direct causality. More experiments are needed to determine whether protecting or disrupting these structures can directly preserve or erase a specific memory.

Why Did Lost Brain Connections Return?

Another remarkable observation concerns dendritic spines.

Dendritic spines are small structures that receive signals from other neurons and are closely involved in synaptic communication. During the artificial hibernation state, many of these spines disappeared.

But after the mice returned to normal conditions, more than 80% of the lost dendritic spines reportedly reappeared in the same locations.

That suggests the brain may retain some kind of underlying molecular or structural information even after a visible connection disappears.

The exact mechanism remains unknown.

One possibility is that the apparent disappearance of a spine does not represent a complete erasure of all molecular information associated with that connection. Some molecular components, cellular scaffolding or positional signals may remain and help guide reconstruction.

This idea could help explain how a highly dynamic brain maintains stable memories.

What This Means for Our Understanding of Memory

For decades, neuroscience has explored the concept of the memory engram, a group of neurons and their connections that collectively represent a specific memory.

The new findings suggest that memory may be more robust than previously assumed.

Instead of storing a memory in a fixed collection of permanent synapses, the brain may preserve the relationships and organization among groups of neurons while allowing individual connections to change.

This resembles a network that can rebuild individual components without losing its overall configuration.

Earlier studies in hibernating animals have already shown that major changes in hippocampal synapses can be reversible. Ground squirrel research, for example, found dramatic structural changes during hibernation followed by rapid recovery after animals warmed up.

The new mouse study adds an important dimension: those structural changes can occur while previously learned memories remain accessible.

For readers interested in how artificial intelligence approaches information organization, this also offers an intriguing conceptual parallel. Neural systems may preserve information through patterns and relationships, rather than relying on one fixed representation.

You can explore more about AI and intelligent information systems on our Features page.

Could This Help Explain Human Memory?

It is important not to overstate the findings.

The experiments were conducted in mice using an artificial hibernation-like state. Humans do not naturally enter the same physiological condition, and the researchers have not demonstrated that the same memory-preservation mechanism operates in people.

Previous animal studies have also produced mixed results regarding memory during hibernation. Some research has reported impaired retention of certain learned tasks, while other studies have found that some animals can retain long-term spatial memories despite extensive remodeling of their dendritic spines.

Therefore, the study is best understood as a new clue about the biology of memory, rather than a direct explanation of human memory.

It could eventually help scientists investigate conditions involving memory loss, brain injury or neural degeneration, but such applications remain speculative.

The Bigger Question: What Actually Stores a Memory?

The study leaves scientists with a deeper question.

If a large proportion of synapses can disappear while a memory survives, perhaps the physical basis of memory is not a single permanent connection.

Instead, memory may be distributed across several layers:

• The identity of neurons involved in an experience
• The spatial arrangement of their connections
• Clusters of synapses
• Multisynaptic structures
• Molecular information retained inside or around neurons
• Broader patterns of neural activity

This could make memories remarkably resilient.

The brain may essentially be able to rebuild parts of its physical network while preserving the information encoded in the network's overall architecture.

That idea could change how scientists investigate long-term memory.

Key Takeaways

• Artificial hibernation caused mice to lose more than half of their hippocampal synapses.
• Despite this dramatic change, the mice retained memories they had learned before hibernation.
• More than 80% of lost dendritic spines reappeared in their original locations after recovery.
• Memory-related synapses appeared to survive preferentially when they were arranged in specific clusters.
• Multisynaptic boutons may help preserve the structural organization associated with long-term memory.
• The findings challenge the idea that a particular synapse must remain unchanged for a memory to survive.

Final Thoughts

The mystery of memory may not be about finding one permanent connection and keeping it unchanged forever.

The new hibernation research suggests something more sophisticated: the brain may preserve memories by protecting patterns, clusters, and network architecture even while individual synapses disappear and return.

For now, the discovery is limited to mice and does not explain exactly how human memories survive. But it offers a compelling new perspective on one of neuroscience's biggest questions.

Perhaps the brain does not store memories like files sitting untouched on a hard drive. Instead, it may preserve them more like a constantly changing network whose essential structure can survive even when many of its individual connections are rebuilt.

Main Topics / About:

• Memory retention and neuroscience
• Hibernation and brain synaptic remodeling
• Hippocampus and memory engrams

Entity Mentions: Science, Okinawa Institute of Science and Technology, hippocampus, synapses, dendritic spines, multisynaptic boutons