A physicist’s fresh look at the ‘prisoner’s dilemma’ reveals hope for cooperation

A Rutgers-led study offers a hopeful twist on a classic game theory problem

Rutgers University

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The “prisoner’s dilemma” is one of the most famous ideas in game theory. It even appeared in the Oscar-winning film A Beautiful Mind, which told the story of mathematician John Nash.

For decades, this game has been used to explain why selfishness often beats cooperation.

In the prisoner’s dilemma, two players can either cooperate or cheat. Cheating always seems to pay off more, so both players end up cheating and losing out even though working together would have given them the biggest reward.

Scientists have long used this idea to understand everything from microbes sharing resources to human societies negotiating peace. The takeaway message? In the evolutionary race, cheaters win.

A new study led by Rutgers physicist Alexandre Morozov turns that assumption upside down. His research, published in the Proceedings of the National Academy of Sciences, shows that cooperation can emerge naturally without special rules or genetic ties.

“The prisoner’s dilemma has told us for 75 years that cheaters always take over in the long run,” said Morozov, a professor in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences. “The end point of any society, based on this, is complete breakdown. But that’s not at all the case. Even in a very simple scenario, cheaters don’t always win. In fact, it’s easier for cooperation to rise.”

Morozov and his collaborator, Alexander Feigel of the Hebrew University of Jerusalem, discovered that the key to cooperation is keeping track of your opponents. If individuals can recognize others, cooperation starts to flourish.

“All you have to do is remember who you interacted with and react in the same way,” said Morozov, who is also director of the Rutgers Center for Quantitative Biology. “That’s enough for cooperation to emerge by itself in many scenarios. It’s what physicists call an emergent property.”

This finding is striking because previous theories required extra conditions such as helping relatives or sticking with your group. Morozov’s model works without those assumptions. It suggests that, even in simple organisms such as microbes or insects, cooperation can evolve if these organisms are able to tell each other apart, perhaps through chemical signals or physical traits.

Game theory underpins this research. A game, in the mathematical sense, is a situation in which players make rational decisions according to defined rules to receive some sort of payoff. Game theory is the branch of mathematics that studies these interactions and helps explain why strategies such as cooperation or cheating emerge in nature and society.

Cooperation is the foundation of complex life, Morozov said. Without it, cells wouldn’t form tissues and societies wouldn’t exist. Yet Darwinian evolution seems to favor selfishness. Morozov’s work offers a new way of understanding how life overcame that hurdle.

“Evolution likes shaping things over long periods of time if it has some material to work with,” Morozov said. “If cooperation always dies off, there’s nothing to evolve. But if there’s a chance, evolution will refine it and make it more stable.”

The implications go beyond biology. Morozov said that his model shows periods of stability interrupted by upheaval, patterns that might sound familiar in human history.

“Cheaters don’t always win,” he said. “Cooperation can persist, and it does persist in many systems scientists look at, such as multi-cellular organisms in which individual cells have to cooperate to survive.”

Morozov started his career as a physicist focusing on protein folding and statistical mechanics, which deals with predicting the behavior of complex systems. Later, he realized those same mathematical tools could help explain how living things evolve. For years, he has explored evolutionary dynamics, building models that show how traits spread in populations under evolutionary forces such as mutation and natural selection.

That experience, Morozov said, gave him the foundation for his latest work. When he encountered game theory during a sabbatical at the Hebrew University, he saw a connection. The same methods he used to study molecules and genes, he realized, could also reveal why cooperation, rather than selfishness, sometimes wins in the prisoner’s dilemma.

The team used mathematical models and computer simulations, including populations of neural networks playing repeated games. A neural network is a computer system modeled after the human brain that teaches patterns and makes predictions by processing information through layers of interconnected nodes.

The scientists also produced a new theoretical result, a generalization of a classic evolutionary principle called Fisher’s fundamental theorem of natural selection.

Morozov said he hopes the work will spark new research on how cooperation evolves in nature and maybe even inspire fresh thinking about cooperation in human societies.

Explore more of the ways Rutgers research is shaping the future.

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2513282123 

Article Title

Emergence of cooperation due to opponent-specific responses in Prisoner's Dilemma

Article Publication Date

22-May-2026

Busseiron and the formation of a discipline in Japanese physics

University of Chicago Press Journals

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The middle of the twentieth century was a period of significant scientific advancement, particularly in the realm of physics. Within this rapidly changing landscape, academic disciplines emerged and evolved to keep pace with scientific discoveries. The new subdiscipline of solid-state physics gained prominence in the United States, but it was later subsumed by the broader category of condensed matter physics. In Japan, however, physics research since the 1940s has included a unique branch called Busseiron—a discipline concerning the study of matter that has no direct English equivalent but that has remained in use nonetheless. A new article by Hiroto Kono in Isis: A Journal of the History of Science Society explores the historical formation of Busseiron and how it was shaped by its specific national context.

The article presents a history of Busseiron as an evolving concept: the word Busseiron was initially used in a pedagogical context in the late nineteenth and early twentieth centuries, but by World War II, the landscape of Japanese physics had expanded greatly and Busseiron came to describe a cluster of research areas. These included magnetism, metal physics, and the emerging field of quantum theory. In a 1942 article, a physicist named Hidetosi Takahasi positioned Busseiron as a counterpart to Soryûshiron (the theory of elementary particles)—a distinction that would continue to shape discourse around the discipline and its boundaries.

Kono describes how Busseiron became more organized throughout the 1940s, with the establishment of several colloquia and a new journal (Busseiron Kenkyû). The field continued to broaden in scope, incorporating new topics such as polymers and low temperatures. This expansion, in part, reflected scientific advances related to wartime technologies. In contrast to the division between academia and engineering that characterized the physics landscape in the United States, Japanese physicists saw Busseiron as a field that bridged the gap between these two spheres.

In the article, Kono surveys various textbooks and other publications from this period that mention Busseiron and finds that a diversity of topics fell within the scope of the field. In fact, by the late 1940s the term Busseiron had become an “umbrella discipline” that incorporated a variety of new and existing topics related to matter. Despite a lack of consensus on what exactly should be included, the dichotomy between Busseiron and Soryûshiron (sometimes characterized as a rivalry) was widely referenced in attempts to classify the field. By the end of the 1940s, the founders of the original Busseiron discipline attempted to corral the expansion of the term by replacing it with the label “chemical physics”—a field growing in popularity overseas. This attempt was largely a failure, as Busseiron already had a foothold in the scientific community and the term was widely accepted. Its definition expanded even further by 1950, with a scope encompassing “almost any research that dealt with matter.”

Kono describes various debates over Busseiron’s structure that arose within the Japanese scientific community in the 1950s and argues that the lack of consistency in defining the term was partly what allowed it to endure into the present day. The name had firmly lodged itself in physicists’ nomenclature and the contentious discussion around it only served to further legitimize its status. As Kono states in the article’s conclusion, “names matter and deserve greater attention in the disciplinary and transnational histories of science.” By tracing discourse around the name Busseiron, this article explores how the Japanese cultural context influenced the genesis of a unique field.

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Since its inception in 1912, Isis has featured scholarly articles, research notes, and commentary on the history of science, medicine, and technology and their cultural influences. Review essays and book reviews on new contributions to the discipline are also included. An official publication of the History of Science Society, Isis is the oldest English-language journal in the field.  

Founded in 1924, the History of Science Society is the world’s largest society dedicated to understanding science, technology, medicine, and their interactions with society in historical context.

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Journal

Isis

DOI

10.1086/740958 

Article Title

Coining a Discipline: The Formation and Perpetuation of a Japanese Branch of Physics of Matter

 

Prior authorization rules vary widely among major commercial insurers

American College of Physicians

          

Below please find summaries of new articles that will be published in the next issue of Annals of Internal Medicine. The summaries are not intended to substitute for the full articles as a source of information. This information is under strict embargo and by taking it into possession, media representatives are committing to the terms of the embargo not only on their own behalf, but also on behalf of the organization they represent.   
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1. Prior authorization rules vary widely among major commercial insurers

Abstract: https://www.acpjournals.org/doi/10.7326/ANNALS-25-05289

URL goes live when the embargo lifts             

A brief research report reviewed the prior authorization rules for Aetna, Humana, and UnitedHealthcare and found little consistency in their prior authorization rules. The findings highlight a fragmented system that may contribute to administrative burden for clinicians and confusion for patients. The report is published in Annals of Internal Medicine.

 

As part of a research program on the potential benefit of standardizing health care contracts, researchers from Stanford University and colleagues examined how prior authorization rules vary across commercial insurers and whether those rules could be organized into a single, searchable database like the ICD-10 system. They analyzed publicly available provider manuals from Aetna, Humana, and UnitedHealthcare, reviewing thousands of procedure and service codes to determine when prior authorization was required and what information clinicians had to submit to the insurer to obtain authorization for a particular test or treatment. Using a combination of automated review and manual checks, they built a searchable database and used it to compare insurer rules. They found that while all three insurers required prior authorization for some services, the majority of services required prior authorization from only one of the three insurers, and the criteria and documentation requirements differed widely. The authors conclude that assembling these rules into a shared database is feasible and could improve transparency for both patients and clinicians, but the unexplained differences across insurers warrant further research on the appropriateness of this administrative barrier to patient receipt of some interventions ordered by their clinician.

 

Media contacts: For an embargoed PDF, please contact Gabby Macrina at gmacrina@acponline.org. To contact corresponding author David Scheinker, PhD please email Errol Ozdalga at eozdalga@stanford.edu and Kara Clemins at kclemins@stanford.edu.

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2. ACP calls for reform of the Medicare Advantage Program to protect patient health

Abstract: https://www.acpjournals.org/doi/10.7326/ANNALS-25-04309

URL goes live when the embargo lifts             

The Centers for Medicare and Medicaid Services (CMS) should reform Medicare Advantage to protect patient health and realign the plan option with its original purpose, says the American College of Physicians (ACP). In a new paper, “Protecting the Integrity and Quality of the Medicare Advantage Program: A Position Paper from the American College of Physicians” published in Annals of Internal Medicine, ACP examines growth of the Medicare Advantage program and its implications for the delivery of fair, high-quality and fiscally responsible care to older adults and people with disabilities.

 

Medicare Advantage is the private option in Medicare that now enrolls more than half of all Medicare beneficiaries. The plans are offered by private insurers approved by the CMS and integrate Part A and Part B of traditional Medicare coverage into a single plan with additional coverage options, such as prescription drugs, dental, vision and even gym memberships. The additional coverage appeals to beneficiaries, but beneficiaries often face challenges in navigating plan choices, unexpected costs, prior authorization and access to clinicians and post-acute services. These barriers disproportionately affect those who are low-income, live in rural communities, or have several chronic conditions. Medicare Advantage risk adjustment policies have created payment vulnerabilities and favorable patient selection, whereas quality measurement of the plans remains fragmented and overly complex.

 

In the paper, ACP details several position statements and recommendations for policymakers to ensure that traditional fee-for-service Medicare remains a strong, sustainable option for beneficiaries and advises that Medicare Advantage plans should not be used to replace or privatize traditional Medicare. These plans also must provide transparent, standardized benefit designs, which would improve beneficiaries' decision making, enhance accountability and ensure that plan offerings prioritize meaningful health benefits rather than serving as an incentive to select a plan. The transparency should extend to the promotion of Medicare Advantage plans, as well. ACP strongly advises robust oversight and regulation of Medicare Advantage marketing practices to prevent misleading advertisements and says that plans engaging in deceptive marketing should face penalties. Medicare Advantage plans should also be required to provide clear, standardized cost disclosures to protect beneficiaries from unexpected financial strain, and CMS should ensure that Medicare Advantage plans prioritize affordability alongside access to care. ACP says the plans should enact balanced and transparent risk adjustment mechanisms to better reflect patient complexity and avoid excessive coding practices.

 

Prior authorization requirements in Medicare Advantage plans are a common concern for physicians and patients due to administrative burden and potential delays in necessary care; ACP calls for streamlined prior authorization processes with faster response times and improved transparency. ACP also recommends that Medicare Advantage plans offer comprehensive and accessible telehealth options to benefit rural and underserved populations. The plans should also report to CMS and the public on the usage and outcomes of supplemental benefits, such as telehealth, dental, vision and hearing services to ensure accountability. Finally, ACP urges policymakers to prevent restrictive contractual clauses in Medicare Advantage models that interfere with physicians’ abilities to serve their patients. Regulatory frameworks should prioritize patient-centered care over administrative or financial considerations.

 

Media contacts: For an embargoed PDF, please contact Gabby Macrina at gmacrina@acponline.org. To speak with someone at ACP, please email Jacquelyn Blaser at jblaser@acponline.org.

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Also new this issue:

How Big Is the “Gray Area”? Navigating Health-Threatening Previability Pregnancy Complications in States With Abortion Restrictions

Alyssa Bilinski, PhD, et al.

Ideas and Opinions

Abstract: https://www.acpjournals.org/doi/10.7326/ANNALS-25-02397  

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Journal

Annals of Internal Medicine

DOI

10.7326/ANNALS-25-05289 

Method of Research

News article

Subject of Research

People

Article Title

Variation in Commercial Insurer Prior Authorization Rules

Article Publication Date

19-May-2026

 

Protein engineering and testing condensed to a single day

Stanford University

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Proteins are critical to life – and to industry. There are countless proteins that could be engineered to treat and even cure serious diseases and cellular dysfunctions. Industrial applications are similarly promising, with proteins increasingly used as enzymes in food manufacturing and in consumer detergents.

While AI can help suggest improvements, each novel protein must still be created in the real world and tested for performance. It is a labor-intensive process that involves constructing the DNA instructions for each protein in yeast or bacteria and growing individual clones for protein production and testing. This can take many days for a single protein of interest and even longer if the protein needs to be tested in mammalian cells, a process that requires retrieving DNA from microbes for transfer to the mammalian cells.

In a new paper, Michael Z. Lin, a professor of neurobiology and of bioengineering in the schools of Engineering and Medicine, and graduate students, Yan Wu in bioengineering and Pengli Wang* in chemical engineering, say they have condensed the time-intensive protein building and testing process to just 24 hours. They call their approach MIDAS for Microbe-Independent Deep Assembly and Screening. MIDAS could rapidly accelerate biological research in fields stretching from oncology to environmental sciences. The study introducing MIDAS appears in the journal Molecular Systems Biology.

“The fundamental questions of molecular biology remain: how do we make better proteins and how do we understand what makes a protein work?” Lin says. “Doing that work takes valuable time and resources, but we’ve found a way to dramatically reduce those demands.”

Going in circles

Lin and colleagues leapfrogged the traditional microbial assembly process by using a genetic replication technique known as polymerase chain reaction (PCR). PCR can amplify linear segments of DNA into millions or billions of copies very quickly. By using PCR to build entire genes used by mammalian cells to express a given protein, they bypassed the need for microbial cloning and DNA transfer. The PCR-produced gene variations can be directly transferred into mammalian cells for functional analysis. The only requirement for the PCR procedure is short strings of DNA known as “primers” that can be ordered for next-day delivery.

“With MIDAS, we can receive PCR primers in the morning, assemble the necessary genes by mid-day, and by late afternoon transfer the genes into cells to observe how the proteins function,” says co-first author Yan Wu. “And we can do this all for hundreds or thousands of protein variants in parallel at a time.”

In traditional protein engineering, when researchers identify a promising variant, they have to assemble and clone the gene expressing the protein into a circular genetic structure known as a plasmid. They must then transfer the modified plasmids into the DNA of bacteria or yeast to produce suitable quantities of each unique plasmid DNA, which must then be transferred into mammalian cells for validation.

This clone-and-transfer process is laborious, slow, and expensive, and it greatly restricts the number of variants that can feasibly be evaluated. MIDAS changes that calculus. Lin and team’s key insight was to do away with the circular plasmids, which are incompatible with PCR. Instead, they treat DNA as linear information that is ideally suited to PCR. This allows them to assemble hundreds of gene variants at a time and directly transfer them into mammalian cells in quantity to identify the best performers quickly and cost-effectively.

With MIDAS, we can receive PCR primers in the morning, assemble the necessary genes by mid-day, and by late afternoon transfer the genes into cells.

Yan Wu

“We decided there’s nothing magical about the circular structure of plasmids,” Lin says. “For PCR, you just need the genetic data. That was the moment of inspiration.”

A practical test of 384 variants using MIDAS took about four hours of hands-on lab work and about $2,000 in reagents. By existing methods, an experienced researcher would need approximately 192 hours and about $20,000 in reagents to evaluate just 24 variants. The researchers calculate that MIDAS is almost 50-times faster and a tenth the cost of cloning-based approaches.

Immediate impact

MIDAS could have immediate real-world implications for biological research. First, it should accelerate important enzyme and biosensor studies, the researchers say. Second, it could improve the automatic production of PCR primers that are ideally suited to modern liquid-handling robots, which can evaluate hundreds of new proteins at a time. Last, and perhaps most importantly, they believe MIDAS could drive better and bigger sequence-fitness datasets that could improve data-intensive AI training, leading to ever more powerful molecular design models.

“We used MIDAS not only to find the best-performing version of a protein but also to understand how well closely related variants work, which is information we can use to train AI models,” says co-first author Pengli Wang. “MIDAS is so easy that we can use it to create large data sets very quickly.”

Looking forward, Lin believes MIDAS could yield deeper combinatorial searches, tighter integration with robotics, and the generation of gene sequence-molecular fitness maps to feed improved machine-learning models that can fuel computational design and experimental validation.

“MIDAS is at least an order-of-magnitude faster at real-world validation,” Lin says. “It compresses the engineering design-build-test cycle for proteins to just a couple of days, and we think it could drive rapid advances in AI-inspired molecular biology.”

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For more information

Contributing authors include Lan Xiang Liu and Daesun Song of Stanford University; and authors from Fudan University, Shanghai, China; and the Promega Corporation. Lin is also a member of Stanford Bio-X, the Cardiovascular Institute, the Maternal & Child Health Research Institute, theStanford Cancer Institute, and the Wu Tsai Neurosciences Institute, and a faculty fellow of Sarafan ChEM-H.

Funding for MIDAS was provided by NIH, a Stanford Bio-X Interdisciplinary Initiatives Program Seed Grant, a Stanford Bio-X PhD Fellowship, and a Stanford Wu Tsai Neurosciences Institute Interdisciplinary Graduate Fellowship.

*Pengli Wang passed away in May 2026 after this research was completed. He was a fourth-year PhD student in chemical engineering.

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Journal

Molecular Systems Biology

DOI

10.1038/s44320-026-00210-z 

Article Title

Fast analysis and engineering of protein function by microbe-independent deep assembly and screening

 

What we now know about how smoking stiffens lungs

Experimental testing on human lungs could improve ventilators

University of California - Riverside

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Video shows a digital model being created from breathing experiments on a lung from a donor. 

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Credit: Mona Eskandari/UCR

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For the first time, scientists have directly measured how smoking changes the mechanical behavior of human lung tissue. 

Published in the Journal of the Royal Society Interface, the study directed by UC Riverside mechanical engineer Mona Eskandari, examines human lung parenchyma, which is the soft, spongy tissue that makes up the bulk of the lung organ. The researchers found that smoking substantially stiffens this tissue in ways resembling fibrosis, a disease that scars and toughens the lungs.

Using human lungs from donors that were either transplant-eligible or designated for research use, the researchers removed small square samples of the parenchyma, then mechanically stretched the tissue while measuring how much force it resisted.

The differences between smokers and nonsmokers were striking. Tissue from smokers became significantly stiffer as it stretched, resisting expansion more strongly than healthy tissue. This is similar to the way scar-like tissue makes breathing progressively more difficult in people suffering from fibrosis.

Though lungs expand in many directions simultaneously with each breath, previous studies stretched tissue in only one direction or relied entirely on animal models. Eskandari’s lab instead conducted tensile tests by extending tissue across multiple axes at once to better mimic the mechanics of real breathing.

The study also revealed that lungs are mechanically nonuniform. Tissue sampled from upper lung regions was generally stiffer than tissue from lower regions, even within the same lobe.

Researchers believe gravity may potentially explain the difference. Because humans stand upright, the upper lungs experience different long-term forces than the lower lungs.

Those uneven mechanics could have important medical consequences. The findings may help explain why certain forms of lung damage, including ventilator-induced lung injury, do not spread evenly throughout the organ. Some regions may be more vulnerable to overstretching than others.

The researchers also measured how much energy lung tissue loses during repeated stretching cycles. Human lung tissue dissipated more energy than researchers typically observe in mice, a finding that may help explain why animal studies do not always accurately represent human lung behavior.

That distinction is increasingly important because scientists are building sophisticated computational “digital twin” lungs designed to simulate breathing, disease progression, and medical interventions. If those models are based only on animal data, Eskandari said, they may fail to capture critical aspects of human lung mechanics and make it harder to use the findings in clinical settings.

The researchers also observed preliminary trends suggesting lungs stiffen with age, though Eskandari cautioned that additional donor samples are needed before drawing definite conclusions. Human donor lungs suitable for this kind of testing are rare, limiting the size of the study.

Even so, the work provides one of the most detailed mechanical datasets yet collected for human lung parenchyma. The findings could eventually improve computational lung models, ventilation strategies, and surgical planning tools designed to predict how diseased lungs respond to physical stress.

Eskandari is the founder of the biomechanics Experimental and Computational Health (bMECH) laboratory at UCR to explore questions about the mechanics of biological tissues. Her cutting-edge research was recently featured in New York Times bestselling author Mary Roach’s new book, Replaceable You: Adventures in Human Anatomy, which explores the evolution of mechanical breathing support.

“We are trying to understand the biological materials we are working with,” said Eskandari. “If we want ventilators and predictive tools that truly reflect how people breathe, these technological advances need to be informed by human-based lung data.” 

​

 

UCR mechanical engineer Mona Eskandari speaking at an invited seminar; Caltech, Pasadena, CA.

Credit

Mona Eskandari/UCR

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Journal

Journal of The Royal Society Interface

DOI

10.1098/rsif.2025.0721 

Article Title

Human lung parenchyma: tensile mechanics and the effects of smoking

Article Publication Date

13-May-2026

 

Silver vine or catnip? When cats can choose, silver vine wins

Cats respond more reliably to silver vine than to catnip, despite catnip’s abundant active compounds

Iwate University, Japan

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The video clip for explaining the article.

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Credit: Reiko Uenoyama

What plant do cats love most?

In Europe and North America, many people would probably answer “catnip.” In Japan, the answer would more likely be silver vine (matatabi in Japanese). Both plants are famous for triggering the well-known feline response: cats rub their faces and bodies against them, roll on the ground, and sometimes lick or chew the leaves.

Previous work by the same research group showed that these plant-derived compounds can repel mosquitoes, suggesting that the behavior may function as a form of natural pest defense. But what happens when cats encounter catnip and silver vine at the same time in a more natural, free-choice setting? Do they choose silver vine, catnip, or both?

A research team from Iwate University and Nagoya University in Japan has found that domestic cats respond more reliably to silver vine (Actinidia polygama) than to catnip (Nepeta cataria) under free-choice conditions. The finding challenges a simple assumption: that a plant containing more active chemical compounds will necessarily produce a stronger behavioral response.

In outdoor experiments in Morioka, Japan, the researchers placed fresh silver vine branches and leaves near living catnip plants in a garden that free-roaming cats could enter and leave. Over ten presentation nights, six identifiable cats were recorded visiting the site. Five of them showed rubbing and rolling behavior toward silver vine, while none showed the same behavior toward either the growing catnip plant or freshly harvested catnip material. The team then compared plant extracts. When catnip and silver vine extracts were presented in the same outdoor setting, cats again showed a stronger tendency to respond to silver vine-derived stimuli.

To test whether this pattern was limited to a small group of local free-roaming cats, the researchers next studied 22 captive purebred cats housed at two facilities in Japan. The cats represented breeds originating from Europe, the United States, and the Middle East. They were tested in a large indoor environment where they could move freely, rather than in individual cages, allowing them to approach, investigate, or ignore the stimuli on their own. When catnip and silver vine extracts were presented simultaneously, 15 cats responded only to the silver vine extract, three responded only to the catnip extract, one responded to both, and three sniffed the papers but did not rub or roll. Overall, cats were significantly more likely to respond to silver vine extract than to catnip extract.

The result was surprising because chemical analysis showed that the catnip used in the study contained abundant active compounds. In fact, the catnip extract contained substantial amounts of cis-trans nepetalactone, a major active compound known to induce the feline response. The total amount of measured bioactive compounds in catnip was about 170 times higher than that in the silver vine extract used in the study.

Further laboratory tests confirmed that these catnip compounds were indeed biologically active. When cats were tested individually in cages, catnip extract and purified nepetalactone isomers found in catnip, compounds made of the same atoms but arranged in slightly different shapes, could trigger the typical rubbing and rolling response. This means that the weak response to catnip under free-choice conditions cannot be explained simply by the absence of active chemicals.

“At first glance, this was counterintuitive,” says Professor Masao Miyazaki of Iwate University, who led the research project. “One might expect a plant containing more active compounds, and compounds that clearly work in laboratory tests, to trigger a stronger behavioral response under free-choice conditions. But that was not what we observed.”

Why cats responded less reliably to catnip remains unclear. One possibility is that fresh catnip may release too much of these active compounds. In other words, the odor may be too strong when cats encounter the living plant. If the odor is intense and continuously released, cats may detect it but be less likely to proceed to rubbing and rolling.

Interestingly, a similar observation was recorded more than 250 years ago. In The Gardeners Dictionary, published in 1768, Philip Miller wrote that cats were especially fond of catmint, now commonly known as catnip, “when it is withered,” but that they tended not to disturb it when a large quantity grew together. Although this was an anecdotal observation rather than a controlled experiment, it closely resembles the pattern suggested by the present study: the amount and presentation of catnip odor may strongly influence whether cats choose to engage with it.

This idea may also help explain why many commercial catnip products use dried leaves. During drying, some volatile nepetalactone isomers may evaporate, possibly reducing the odor to a level that is more effective for inducing the feline response.

“Catnip can make cats respond in laboratory tests, but that does not mean cats will choose it in a more natural, free-choice setting,” says first author Reiko Uenoyama, an assistant professor at Iwate University. “Our study shows that what cats can respond to and what they actually choose are not always the same.”

The findings suggest that real-world behavior depends not only on the presence of active compounds, but also on how the odor is presented and whether animals voluntarily approach and interact with it.

“This study suggests that silver vine is a particularly reliable stimulus for inducing cats’ self-anointing behavior,” says Professor Miyazaki. “It also reminds us that animal behavior should be studied in settings where animals can make their own choices.”

These insights may help improve enrichment materials for domestic cats and provide a broader framework for understanding how chemical cues influence animal behavior in real-world environments.

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Journal

Journal of Chemical Ecology

DOI

10.1007/s10886-026-01717-3 

Method of Research

News article

Subject of Research

Animals

Article Title

Free-Roaming and Captive Cats Prefer Silver Vine to Catnip for Self-Anointing

Article Publication Date

12-May-2026