What can a rat’s ultrasonic call tell us about food-related pleasure?

A newly identified vocal signal may indicate that rats vocally express their enjoyment of eating

University of Fukui

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The researchers wanted a more direct, non-invasive way to assess how much an animal enjoys food, beyond simply measuring food intake. While recording rats during chocolate feeding, they noticed that the rats produced a characteristic vocalization while eating. This led them to investigate whether these calls carried information about how much they enjoyed the food.

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Credit: Dr. Koshi Murata from University of Fukui, Japan

Understanding how the brain processes rewarding experiences could help researchers better understand behaviors such as overeating, as well as conditions such as anhedonia—the inability to experience pleasure, which is a common symptom of depression. One way researchers study reward-related processes is through animal models. In rats, ultrasonic vocalizations (USVs), sounds that are too high-pitched for humans to hear, are associated with various emotional and motivational states, including responses to rewarding stimuli. Previous studies found that rats produce these vocalizations when they consume sweetened foods and even when they anticipate receiving them.

Now, researchers, including Assistant Professor Koshi Murata, Dr. Yuki Ikedo, and Dr. Yugo Fukazawa, at the Division of Brain Structure and Function, Faculty of Medical Sciences, University of Fukui, Japan, have identified a distinct subtype of USV—the 40 kHz inverted-U USV—that rats produced more frequently while consuming highly palatable chocolate. The researchers suggest that these vocalizations could provide a measurable signal associated with palatable food consumption and help investigate the brain mechanisms underlying food-related reward and positive emotional states, with potential relevance to conditions such as overeating and obesity.

This paper was made available online on July 17, 2026, and was published in Volume 13, Issue 8 of the journal eNeuro on August 01, 2026.

“When rats eat something delicious such as chocolate, they emit a distinct ultrasonic call that humans cannot hear. This call drops sharply when the brain's opioid ‘pleasure’ system is blocked. This suggests that rats may be vocally expressing the enjoyment of eating, offering a new window into whether animals experience pleasure as we do,” says Dr. Murata.

In their experiments, the researchers first recorded USVs from rats to identify patterns associated with chocolate consumption. They compared the sounds produced when the rats had access to chocolate with those recorded during baseline periods, and with those from a control group of rats that were not fed chocolate. Using machine learning to analyze the acoustic features of these vocalizations, they identified a distinct 40 kHz inverted-U USV that was strongly associated with chocolate consumption.

The researchers also found that administering naloxone, which blocks opioid receptors, reduced these vocalizations during chocolate consumption. This suggests that the endogenous opioid system, which is involved in processing reward-related and hedonic processes, may influence the production of these vocalizations. The researchers then investigated whether these vocalizations were related specifically to the palatability of the food or were simply a general response to eating. To find out, they compared the vocalizations rats produced while eating chocolate and regular chow. Although the rats consumed similar amounts of both foods, they produced significantly more 40 kHz inverted-U USVs while eating chocolate. The rats also showed a clear preference for chocolate in a separate food-choice test, with 15 of the 16 rats choosing chocolate over regular chow.

The researchers also found that 97.2% of 40 kHz inverted-U USVs occurred within 1 second of a feeding event in the initial experiments. This close temporal association was reproduced in an independent test group, in which 96.6% of these calls occurred within 1 second of feeding.

Together, these results suggest that 40 kHz inverted-U USVs do not simply reflect the act of eating. Instead, the rats produced these vocalizations more frequently when consuming the more palatable food. This suggests that the calls may reflect the rats’ internal state while eating highly palatable food. This finding could open up new ways to investigate positive emotional states in animals and further study the brain mechanisms involved in reward and pleasure.

“Our discovery suggests that animal vocalizations could serve as a real-time, non-invasive readout of internal emotional states—specifically, how much an animal is enjoying its food. Such a tool would allow researchers to measure ‘pleasure’ more directly than current methods permit, and could accelerate research into the brain mechanisms that generate positive emotions,” says Dr. Murata.

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Reference
Title of original paper: A Subtype of Ultrasonic Vocalizations during Palatable Food Consumption in Rats Identified by Machine Learning-Assisted Classification
Journal: eNeuro
DOI: https://doi.org/10.1523/ENEURO.0356-25.2026

About University of Fukui, Japan
The University of Fukui is a preeminent research institution with robust undergraduate and graduate schools focusing on education, medical and science, engineering, and global and community studies. The university conducts cutting-edge research and strives to nurture human resources capable of contributing to society on the local, national, and global level.

Website: https://www.u-fukui.ac.jp/eng/

About Assistant Professor Koshi Murata from University of Fukui, Japan
Dr. Koshi Murata is an Assistant Professor in the Division of Brain Structure and Function, Faculty of Medical Sciences, University of Fukui. His research explores the neural mechanisms underlying reward, motivation, and sensory processing, particularly in relation to food consumption and motivated behaviors. He uses machine learning-assisted analysis of ultrasonic vocalizations, deep learning, and molecular genetics in rodent models. His work examines the roles of dopamine and opioid systems in shaping behavior.

Funding information
This work was supported by Lotte Research Foundation, Urakami Foundation for Food and Food Culture Promotion, Takeda Science Foundation (TSF), and Japan Society for the Promotion of Science (17KK0190, 20H05955, 21H05817, 21K06440, and 24K02131).

 

Researchers compared the ultrasonic calls rats produced before and after receiving chocolate. Analysis of their acoustic features revealed distinct differences in the calls produced during chocolate feeding, helping researchers identify vocalizations associated with palatable food.

Credit

Dr. Koshi Murata from University of Fukui, Japan

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Journal

eNeuro

DOI

10.1523/ENEURO.0356-25.2026 

Method of Research

Experimental study

Subject of Research

Animals

Article Title

A Subtype of Ultrasonic Vocalizations during Palatable Food Consumption in Rats Identified by Machine Learning-Assisted Classification

 

Denver Museum of Nature & Science discovers first-ever adult T. rex trackway

Massive footprints preserve a 66.5-million-year-old walk through North Dakota

Denver Museum of Nature & Science

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DENVER — Scientists from the Denver Museum of Nature & Science and Liverpool John Moores University in England have discovered the first adult T. rex trackway, providing insights into how this emblematic predator moved. The findings were published today in the Journal of Vertebrate Paleontology. 

The approximately 23-foot-long trackway consists of four three-toed footprints discovered in the Hell Creek Formation of southwestern North Dakota. Each footprint is roughly 3 feet long, and researchers estimate they were made about 66.5 million years ago.  

The team identified T. rex as the most likely trackmaker based on the footprints’ exceptional size and narrow shape of the toes, along with the abundance of T. rex fossils found in the surrounding area. While isolated footprints have been attributed to adult T. rex in the past, this is the first time scientists have described a sequence of tracks, or trackway, likely left by this most famous of dinosaurs.  

“Bones tell us an enormous amount about these animals, but footprints capture a moment of behavior. With a trackway, we can actually follow an animal as it moved across the landscape. That is incredibly rare for T. rex,” said Tyler Lyson, senior curator of vertebrate paleontology at the Denver Museum of Nature & Science. 

The trackway was found in 2025 on federal land administered by the U.S. Forest Service near Marmarth, North Dakota. The team used high-resolution 3D surface scanning to document each footprint and the full trackway. The resulting digital models allow scientists to examine the tracks in detail and create physical 3D reproductions.  

Peter Falkingham, a professor of palaeobiology at Liverpool John Moores University and a dinosaur track expert, was lead author of the study, despite never having seen the tracks in person. “The technology we’re able to apply in the digital age means my colleagues could scan the tracks in the field and then send the 3D information over to me to visualize on my computer and in VR, enabling me to take as close a look as they did in person,” he said. 

The trackway records two left and two right footprints, with a stride of approximately 13 feet. Researchers estimate the animal was walking about 3.5 to 4.5 mph, roughly comparable to a brisk human walking pace. Because the tracks are heavily weathered, the speed estimate is approximate. 

“As a teacher, I’m always telling my students that science starts with curiosity, passion and careful observation. I never imagined that could lead me to a discovery like this,” said Kent M. Hups, a teacher at Northglenn High School who discovered the site and co-authored the paper.  

Three of the footprints are expected to be recovered by helicopter this fall and then transported to the Denver Museum of Nature & Science. The Museum plans to share updates from the recovery with guests this winter.  

Other members of the research team are Museum researchers Evan Tamez-Galvan and Antoine Bercovici. Lyson led the fieldwork and Tamez-Galvan conducted the surface scanning.  

Follow the link for media assets, including field photography, 3D imagery and paleoart. 

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About the Denver Museum of Nature & Science  

The Denver Museum of Nature & Science is the Rocky Mountain region’s leading resource for formal and informal science education. Many of the Museum’s educational programs and exhibits are made possible in part by the citizens of the seven-county metro area through the Scientific & Cultural Facilities District. The Museum is accredited by the American Alliance of Museums. Connect with the Museum on Facebook, Instagram and TikTok and explore more Museum stories on Catalyst. 

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Journal

Journal of Vertebrate Paleontology

DOI

10.1080/02724634.2026.2706201 

Method of Research

Imaging analysis

Subject of Research

Animals

Article Title

A LARGE TRIDACTYL TRACKWAY FROM THE UPPER CRETACEOUS HELL CREEK FORMATION OF NORTH DAKOTA, LIKELY ATTRIBUTABLE TO AN ADULT TYRANNOSAURUS REX

Article Publication Date

8-Sep-2026

 

Heatwaves inhibit antibiotic resistance in soils, but at a price

Universiteit van Amsterdam

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Extreme heatwaves disrupt life in soil. Soil bacteria that produce and resist antibiotics switch into survival mode, temporarily reducing the number of resistance genes. At the same time, heat and drought are causing significant damage to soils and ecosystems, especially in cold, wet regions such as the Netherlands. This is evident from a large-scale European study by soil ecologist Franciska de Vries (University of Amsterdam) and colleagues.

According to De Vries, many people are unaware that soils form an important reservoir of both antibiotics – which we can extract – and resistance genes. ‘In the soil, there is a kind of “war” going on: bacteria both produce antibiotics and arm themselves against them with resistance genes,’ she explains.

At warm temperatures and in wetter conditions, the number of resistance genes increases. Bacteria then become insensitive to antibiotics and can pass this trait on to other bacteria. It becomes problematic when those genes end up in pathogenic bacteria that infect humans or animals.

It has often been assumed that climate change accelerates the spread of resistance genes. But what happens during extreme weather conditions such as heat, drought and floods that occur not slowly, but suddenly?

Soils from across Europe

‘Before we got to that specific question, we first wanted to understand in general how soil organisms respond to extreme weather conditions,’ says De Vries. ‘Soils, for example, are very important for sequestering CO₂. What happens to this function during extreme weather?’

With her colleagues, she collected soils from all over Europe: ‘From Iceland to Greece and from Sweden to Spain and even the Russian steppe.’ The researchers exposed these soils to extreme conditions in climate chambers: severe drought, flooding, alternating frost and thaw, and a short but intense heatwave.

Hot soils can handle more than wet, cold soils.

The researchers turned out to be very good at predicting how certain soils react to extremes. ‘Quite logically, hot soils can withstand heat better than cold and wet soils like those we have in Sweden, Iceland and the Netherlands,’ says De Vries.

‘Soils from warm, dry countries are already accustomed to heat and drought,’ she adds. ‘The soil organisms there remain relatively stable when the weather becomes extreme. In cold, wet soils, bacteria and fungi are disrupted much more quickly by heat and drought. Those soils then lose their functions, such as CO₂ storage, more easily. And it is primarily these areas that are warming up significantly.’

What do climate extremes do to resistance genes?

In a new collaboration and using new DNA techniques, the question subsequently arose as to what effect these extreme conditions have on the type and quantity of resistance genes in soils. And whether this is also accurately predictable.

Droughts, floods and freeze-thaw periods were shown to cause only mild changes in the resistance repertoire. Moreover, these responses were reasonably predictable based on climate and soil type.

Heatwaves, however, stood out. The reactions that arose from them were the least predictable, and bacteria really struggled. ‘They exchange fewer resistance genes and produce fewer antibiotics,’ says De Vries. ‘That was very surprising: just like plants, they also go into survival mode. And after such an extreme, those genes don't grow back quickly either.’

Location proves decisive

Geography proved to be the most important indicator. ‘Where the soil comes from is more important than what extreme weather is unleashed upon it,’ says De Vries. ‘Wet soils find it much harder to cope with drought and heat, whereas we saw much larger quantities of resistance genes in countries like Greece and Spain.’

Not necessarily good news

At first glance, it could appear to be good news that heatwaves temporarily reduce the amount of resistance genes in the soil. However, De Vries warns, the heat and droughts are also causing significant damage to soils and ecosystems. The temporary dip in resistance therefore does not mean that the health risks from antibiotic resistance disappear.

‘We now know that climate extremes do not always affect antibiotic resistance in the same way,’ De Vries concludes. ‘That knowledge helps us more easily predict where the real risks lie and to tailor policy and monitoring specifically to particular soils and regions.’

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2612278123 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Extreme climatic events drive consistent and predictable shifts in soil antibiotic resistance genes

Article Publication Date

4-Sep-2026

 

As probiotic use surges, microbiome-supportive food consumption stagnates

The proportion of young people taking probiotic supplements rose 786% in 14 years

Michigan Medicine - University of Michigan

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New research finds that probiotic supplement use has surged in the United States, while the consumption of microbiome-supportive foods has remained virtually unchanged.

According to a study published in Clinical Gastroenterology and Hepatology, the consumption of probiotic supplements increased 287% among adults from 2009-2023 and 786% among young people (less than 20 years old).

Over the same span, fiber intake did not meaningfully change, while the average consumption of high microbial foods rose slightly.

“We have known that probiotic supplement use is increasing across all ages, but this is the first time we have looked closely at it in relation to other microbiome-focused health behaviors,” said Kira L. Newman M.D., Ph.D., Clinical Assistant Professor of Internal Medicine at the University of Michigan Medical School and lead author on the paper.

“Dietary fiber and fresh produce have well-established health benefits for the gut microbiome. However, our findings suggest that people are not making changes to what they eat, even though an increasing number are concerned enough about their microbiome to take a probiotic supplement.”

The study authors used data from the National Health and Nutrition Examination Survey.

From 2009 to 2023, the proportion of people under 20 taking a probiotic rose from 0.63% to 5.58%.

Among people over 20, the percentage increased from 1.8% to 6.96%.

Probiotic supplement users were found to consume more foods high in microbial quality and fiber content than non-users.

Researchers add, however, that these beneficial diet habits may be decreasing, as supplements are potentially used as a substitute for higher-quality diets.

Probiotic supplement use increased dramatically after 2014 despite official guidelines suggesting limited benefits.

The study authors note a variety of health benefits associated with high microbial foods.

They emphasize that these benefits are not necessarily related to microbial content.

“A diet with plenty of vegetables, fruits, legumes, and whole grains provides not just fiber, but also a wealth of other beneficial vitamins, minerals and plant-derived compounds,” Newman said.

“This helps support a diverse range of beneficial gut microbes. Prebiotic supplements alone do not contain the same variety or richness. It’s like picking one color out of a rainbow.”

The study authors hope these trends will highlight the need for more public health campaigns on the importance of diet in fostering microbiome health.

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Journal

Clinical Gastroenterology and Hepatology

DOI

10.1016/j.cgh.2026.08.029 

Method of Research

Data/statistical analysis

Subject of Research

People

Article Title

Increases in Probiotic Supplement Use Exceed Microbiome-Focused Dietary Changes in US Adults and Children

Article Publication Date

7-Sep-2026

COI Statement

Kira L Newman, MD, PhD consults for Takeda and has research support from Pfizer. Allen A Lee, MD, MS consults for GSK and Atmo Biosciences. William D Chey, MD consults for Ardelyx, Atmo, Gemelli, Phathom, Redhill, Salix, Vibrant; research support from Commonwealth Diagnostics, NIH, FDA, Salix; stock options in Coprata, Evinature, Food Marble, Isothrive, Kiwi Bioscience, Modify Health; patents for My Nutrition Health, Digital Manometry, Rectal Expulsion Device. Peter DR Higgins, MD, PhD consults for AbbVie and Curacle. Prashant Singh, MBBS, and John Y Kao, MD, have no conflicts to disclose.

THE DEEP STATE IS INCOMPETENT

Widespread COVID death underreporting around the world raises broader questions about the reliability of official information

The Hebrew University of Jerusalem

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Deriving covid misreporting. Notes: The left panel shows periodical (weekly or monthly) mortality and expected mortality from 2015 to 2021 in solid lines, and reported Covid mortality in dashed lines. The right panel shows the cumulative officially-reported Covid deaths in 2020-21, and our estimated Covid deaths (difference between actual and expected mortality, minus excess deaths due to non-Covid factors.

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Credit: Credit: Ariel Karlinsky

 News Release 9-Sep-2026

New study finds that widespread underreporting of Covid-19 deaths cannot be explained simply by differences in countries’ ability to count and record deaths. Across 134 countries and territories, an estimated 45%–55% of governments misreported Covid mortality, with underreporting far more common than overreporting. The study provides comparable country-level data of the extent of misinformation for researchers and policymakers. The findings point to a broader lesson beyond the pandemic: strong institutions and an informed public can play an important role in protecting the reliability of official information.

During the Covid-19 pandemic, governments around the world faced the same basic challenge: measuring a fast-moving public-health crisis and communicating its severity to citizens.

But did official data reflect what was actually happening?

A new study by Ariel Karlinsky (Hebrew University) and Prof. Moses Shayo (Hebrew University & King’s College London), suggests that in many countries they did not. Published in the Journal of Economic Growth, the research compares officially reported Covid deaths with estimates based largely on excess mortality, deaths above the number that would normally have been expected.

Using Covid as a Global Test Case

Karlinsky and Shayo assembled mortality data from 134 countries and territories, drawing on national statistical offices, population registries, health ministries and other sources.

Across the countries studied, governments reported 5.08 million Covid deaths in 2020 and 2021, while the researchers estimate actual Covid mortality at 12.47 million. Their analysis indicates that roughly 45%–55% of governments misreported Covid mortality, with underreporting far more common than overreporting.

Importantly, the researchers do not assume that every reporting gap represents deliberate manipulation. Countries differ in their ability to diagnose illness, register deaths and maintain reliable statistical systems. The study therefore examines whether differences in state capacity can explain the discrepancies.

Capacity explains only a small share of the variation.

Why Institutions Matter

A stronger relationship emerges when the researchers examine the constraints governments face.

Countries with stronger institutional checks and balances show much less underreporting. Misreporting is also lower where citizens are better positioned to evaluate official information, measured through factors including education and internet access.

The authors also find higher levels of misreporting in countries holding elections during the pandemic and in countries with a communist legacy, although they emphasize that these relationships are descriptive and do not establish causation.

The broader finding is that incentives to present information favorably may exist in many political systems. What appears to matter is whether governments face effective institutional and social checks that make inaccurate information easier to detect and challenge.

Why This Matters Beyond Covid

Covid offered researchers an unusual opportunity: governments around the world confronted a broadly comparable crisis at roughly the same time.

But the implications extend beyond public health.

Governments routinely produce statistics that influence decisions about economic growth, unemployment, public health, international aid and other major policy issues. During Covid, reported figures also influenced international decisions, including travel restrictions.

The study argues that inaccurate official information can therefore have consequences far beyond the country producing it, complicating international efforts in areas such as foreign aid, climate action and vaccination campaigns.

This question has become even more relevant in today's fast-moving information environment, where misleading claims can spread rapidly through digital platforms and AI-generated content.

Looking Beyond the Headline Number

One of the study's key contributions is its use of excess mortality as an independent benchmark.

Official Covid deaths depended on identifying Covid as a specific cause of death, which could be affected by testing and reporting practices. Excess mortality instead asks a simpler question: How many people died compared with how many would normally have been expected?

Comparing the two allowed the researchers to identify reporting gaps that could not easily be explained by differences in countries' statistical capacity alone.

The principle extends beyond Covid: important official claims become more reliable when they can be tested against independent evidence.

Trust Depends on Verification

The findings do not suggest that official statistics should automatically be distrusted. Rather, they demonstrate why systems capable of independently verifying, challenging and correcting information matter.

Karlinsky and Shayo find that governments facing stronger institutional and social constraints generally report more accurately, while those facing fewer constraints show larger discrepancies.

Covid therefore provides more than a case study in pandemic mortality. It offers a window into a much broader question: What makes official information trustworthy?

The research suggests that part of the answer lies not only in governments' ability to produce good data, but also in the strength of the institutions and societies capable of holding those governments to account.

 

Misreporting rate (MRR) by country. Notes: The figure shows the Misreporting Rate (MRR) for 131 countries, ranked from highest (estimated deaths higher than reported) to lowest. Countries where the estimated MRR is insignificantly different from 0 (accurate reporting countries) are shown in the inset. The point estimates of the MRR in the accurate reporting countries ranges from 9% to 15% . Bhutan, Fiji and Vietnam do not have sufficient data to estimate a CI, and are excluded from this figure. Their MRRs are 3.2% , 9.7%  and 9.8% , respectively.

Credit

Credit: Ariel Karlinsky

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Journal

Journal of Economic Growth

DOI

10.1007/s10887-026-09266-w 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Manipulation of information in times of crisis: Evidence from Covid excess mortality