How Tiny Rodents Are Unlocking the Secrets of the Brain
It's a quiet evening in a research laboratory, and a golden hamster hesitates at the entrance to a Y-shaped maze. His whiskers twitch as he detects a familiar scent down one pathway—the male that defeated him in a fight just yesterday. Instead of proceeding, he retreats to safety. This simple decision, observed and measured by scientists, represents something extraordinary: a complex memory at work, a detailed recollection of another individual and the emotional experience they represent.
Did you know? The similarities between hamster and human brains are striking enough that Cornell University professor Robert Johnston notes, "They are more sophisticated than you might think" 7 .
What can a hamster possibly tell us about our own brains? As it turns out, quite a lot. Despite their small size, hamsters have become unexpected heroes in neuroscience, helping researchers unravel the mysteries of how brains recognize individuals, form spatial memories, and how these processes can be disrupted by diseases and infections. From social interactions to the devastating impacts of long COVID, studies of hamster memory are providing critical insights into fundamental brain mechanisms that humans share with these furry creatures.
Hamsters demonstrate true individual recognition, not just distinguishing familiar from unfamiliar scents.
Their brain similarities to humans make hamsters valuable models for studying memory processes.
In a sobering 2025 study published in Nature Communications, researchers made a startling discovery about the long-term effects of SARS-CoV-2 infection in hamsters 1 3 9 . Even after the hamsters had recovered from the initial acute infection and appeared clinically healthy, viral RNA and even infectious virus persisted in their brainstems for at least 80 days after the original infection.
The study followed hamsters infected with different SARS-CoV-2 variants—Wuhan, Delta, and Omicron/BA.1—and found that although all variants reached the brain, they did so with varying efficiency. Most remarkably, researchers were able to isolate and amplify infectious SARS-CoV-2 from the brainstems of 75-87.5% of infected hamsters at 80 days post-infection, despite the animals showing no outward clinical signs of illness 1 .
| Variant | Genomic RNA Detection at 80 days | Infectious Virus Isolation at 80 days | Key Behavioral Changes |
|---|---|---|---|
| Wuhan | Detected in all animals | 75% of animals | Depression-like behavior, memory impairment |
| Delta | Detected in all animals | 87.5% of animals | Depression-like behavior, memory impairment |
| Omicron/BA.1 | Detected in all animals | 75% of animals | Depression-like behavior, memory impairment |
Transcriptomic analysis of the infected hamsters' brainstems revealed a disturbing neurodegenerative molecular signature characterized by 1 3 :
These molecular changes translated into measurable behavioral deficits. The infected hamsters exhibited persistent depression-like behavior, impaired short-term memory, and late-onset anxiety—symptoms that closely mirror the neuropsychiatric symptoms reported in humans suffering from long COVID 1 .
The impact of infections on hamster memory isn't limited to viruses. In a 2019 study published in Scientific Reports, researchers examined how hookworm infections affect spatial memory . Using the Displaced Object Recognition (DOR) task, they tested hamsters' ability to notice when objects in their environment had been moved—a measure of spatial memory.
The researchers found that hookworm-infected hamsters showed significant impairments in spatial memory compared to their uninfected counterparts. While uninfected hamsters readily noticed and explored displaced objects, infected hamsters struggled to detect these spatial changes. The deficit was dose-dependent—the higher the infection burden, the more severe the memory impairment .
| Infection Level | Ability to Detect Displaced Objects | Statistical Significance | Interpretation |
|---|---|---|---|
| Uninfected | Strong preference for displaced object | p < 0.0001 | Normal spatial memory |
| Low infection | Moderate preference for displaced object | p = 0.016 | Mild spatial memory deficit |
| Moderate infection | No preference for displaced object | p = 0.52 | Significant spatial memory deficit |
| High infection | No preference for displaced object | p = 0.92 | Severe spatial memory deficit |
Researchers employ several sophisticated behavioral tests to assess different aspects of hamster memory and cognition 2 6 :
Measures individual recognition and social memory
Assesses spatial memory by testing detection of moved objects
Evaluates innate behaviors sensitive to brain lesions
Measures motor deficits and general welfare
Assesses locomotor activity and anxiety-related behaviors
Specifically designed to measure anxiety-like behaviors
To identify the brain regions involved in memory processes, scientists use several techniques 2 7 :
Visualizes recently active neurons by targeting proteins produced by active brain cells
Allows researchers to determine if specific brain regions are necessary for particular memory tasks
Examines gene expression patterns in brain tissue to identify molecular pathways involved in memory processes
| Tool/Technique | Primary Function | Example Use in Hamster Studies |
|---|---|---|
| Immunohistochemistry | Visualizes recently active neurons | Mapping brain regions activated during individual recognition 2 |
| Y-maze apparatus | Tests social recognition and memory | Measuring avoidance of familiar aggressive males 2 4 |
| Transcriptomic analysis | Identifies gene expression changes | Revealing neurodegenerative signatures in long COVID model 1 |
| Temporary brain inactivation | Determines necessity of brain regions | Establishing hippocampal role in recognition memory 2 |
| Displaced Object Recognition (DOR) | Assesses spatial memory | Detecting hookworm-induced memory deficits |
As we've seen, the humble hamster has provided remarkable insights into how brains form, store, and retrieve memories—and how these processes can go awry. From social recognition to spatial navigation, these creatures have helped map the neural circuits of memory and demonstrated how infections ranging from SARS-CoV-2 to hookworms can disrupt cognitive function.
| Study Type | Primary Memory Type Affected | Underlying Mechanism | Duration of Impairment |
|---|---|---|---|
| Social defeat memory | Individual recognition | Hippocampal-dependent emotional memory | At least 7 days 4 |
| SARS-CoV-2 infection | Short-term memory, emotional processing | Brainstem inflammation, neurodegenerative changes | At least 80 days 1 |
| Hookworm infection | Spatial memory | Gut-brain axis disruption, nutritional deficits | During acute infection |
As research continues, hamsters will likely remain essential partners in unraveling the remaining mysteries of memory. Their brains, though small, continue to illuminate fundamental truths about how all brains remember, recognize, and navigate their worlds—proof that sometimes the most profound discoveries come in the smallest packages.
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The Social Brain: How Hamsters Recognize Friends and Foes
The Y-Maze of Social Memory
In a landmark series of experiments that read like a rodent drama, researchers developed clever methods to test how hamsters recognize and remember each other as distinct individuals 2 4 . The experiments unfolded in three phases:
Habituation
A male hamster first became familiar with a Y-shaped maze.
Social Experiences
The subject hamster then had different interactions with two other males—peaceful encounters through a wire mesh with one, and aggressive fights with another that ended in defeat.
Testing
The following day, the hamster was placed back in the Y-maze with one of the familiar males confined in a stimulus chamber.
The results were striking and consistent: when the hamster detected the scent of his former conqueror, he actively avoided that arm of the maze. But when he encountered the male he had peacefully met through the barrier, he was actually attracted to the scent 2 7 . This demonstrated something far more sophisticated than simply distinguishing familiar from unfamiliar—the hamster was showing true individual recognition and attaching appropriate emotional responses based on past experiences.
Mapping the Social Brain
By examining the hamsters' brains after these tests, researchers identified the specific regions responsible for these memory feats. Using immunohistochemistry—a technique that leaves a colorful "map" of recently active brain cells—scientists found activity in several key areas when hamsters recognized individuals 2 7 :
When researchers temporarily numbed the CA1 region of the anterior dorsal hippocampus using lidocaine, the hamster no longer avoided the familiar winner 2 . This provided compelling evidence that this region is necessary for recognition memory—a finding with direct relevance to human brains, where the hippocampus has also been implicated in recognition memory 7 .