Sleeping alongside your dog probably doesn’t disrupt your sleep as much as you might think, according to a study published in the open access journal PLOS One by Ming Fei Li of the University of Toronto, Canada, Lavania Nagendran of the University of Toronto Mississauga, Canada, and colleagues.

It is intuitive to think that humans and their dogs affect each other’s sleep schedules, but little research has been done in this area and with conflicting results. In this study, Li, Nagendran and colleagues examined the nighttime activity of 25 humans and their 38 dogs to investigate how they impacted each other’s nighttime experience for better or worse.

Over a period of four weeks, results from activity monitors – worn on the wrist for humans and on the collar for dogs – found that sharing the bed with a dog did not significantly impact sleep duration or sleep quality, even in cases where owners reported feeling like their dogs were disturbing their sleep.

Nighttime activity was strongly correlated, with humans and their dogs commonly becoming active around the same time in the night, but more often than not the humans began moving before the dogs did, suggesting that owners are disturbing their dog’s sleep more than the other way around.

Thus, the answer to the question of “who is disturbing whom” seem to be a bit of both. These results align with some previous research on the benefits and drawbacks of co-sleeping with dogs, but the authors note that this study includes a limited sample and no dog-less control group. Therefore, future studies will be needed to include more data on dogs of different ages and breeds.

The authors add: “Our findings suggest that nighttime activity in humans and dogs is closely coupled and there may be discrepancies between objective and subjective sleep measures.”

Why do large dogs tend to live shorter lives than their smaller counterparts? According to a study of nearly 900 dogs, the answer may be written into their epigenome. The findings reveal that larger and male dogs undergo accelerated molecular aging, with pronounced DNA methylation (DNAm) on the X chromosome and at transposable elements (TEs).

Aging is a universal process, but its pace and biological mechanisms substantially differ between individuals and species. Domestic dogs offer a particularly useful model for understanding the biology of aging because their lifespans vary dramatically with body size.

For example, smaller breeds can live nearly twice as long as larger breeds. Moreover, companion dogs also live in human environments, consume commercial diets, and receive routine medical care, making them a relevant translational model for studying how genetic background and environmental exposures shape aging.

However, how intrinsic factors such as size and biological sex influence variation in dog aging and lifespan remains unclear. Previous research has demonstrated that DNAm is a useful indicator of biological aging, with “epigenetic clocks” offering a way to understand the factors that accelerate or decelerate biological aging.

Blaise Mariner and colleagues generated 1,640 methylomes from a cohort of 894 dogs in the Dog Aging Project. They combined these molecular data with detailed genetic and demographic data.

Mariner et al. found that molecular aging occurs most rapidly early in a dog’s life. What’s more, larger and male dogs – both of which have shorter lifespans than their respective counterparts – age more quickly at the molecular level.

The authors identified different epigenetic patterns underlying these effects. According to the findings, sex-related changes were concentrated on the X chromosome, while body-size-related changes were especially prominent in TEs, stretches of DNA that can influence genome stability and gene regulation.

Scientists—and dog lovers—have long known that dogs are remarkably good at interpreting our laughs, frowns, and tears. But the biology behind this ability has remained largely unexplored until now. 

In a study published in the Cell Press journal iScience, researchers peered inside the brains of dogs as they viewed images of various human expressions. The brain scans revealed that dogs process smiles in a unique brain region and, for the first time, provided evidence that dogs can distinguish between negative facial expressions, including anger, sadness, and fear. 

“Humans are really good at picking up small details on the face, and so are dogs,” says first author Raúl Hernández-Pérez from the University of Vienna. “This makes dogs very interesting. By studying their brains, we can understand what adaptations have developed to support their remarkable social and emotional understanding of humans.” 

The researchers first focused on happiness, an expression that previous studies suggest holds particular significance for dogs. They scanned eight dogs while showing them images of strangers with either happy or neutral expressions. The happy faces lit up the temporal cortex and caudate nucleus in the dogs’ brains—regions associated with higher cognitive and reward processing, respectively. 

“The activity in the caudate nucleus is particularly interesting,” says Laura Cuaya, also of the University of Vienna, who began the research at the National Autonomous University of Mexico and later expanded it through a collaboration at Eötvös Loránd University in Hungary. “It suggests that happy human faces may have emotional significance for dogs.” 

The team then asked whether the same brain regions respond to other emotions. They showed images of people displaying happiness, anger, fear, and sadness to 12 dogs and analyzed their brain activity using machine learning. They found that the dogs did not react in the same to these negative emotions; the temporal cortex-caudate nucleus network responded uniquely to happiness, allowing researchers to easily distinguish brain reactions to smiles from all three negative expressions.  

But the canine brain was not merely sorting the world into good and bad, the team found. A whole-brain analysis revealed distinct patterns of activity that separated fear from anger and sadness, providing the first evidence that dogs can distinguish between specific negative facial expressions.  

The researchers say that this ability does not mean that dogs experience emotions exactly as humans do. Also, a still photo of a human face doesn’t tell the whole story; in real life, dogs watch human body language, listen to nuances in our voices, and detect information from our scent. 

“When we compare humans with primates, we are looking at abilities that may have come from a common ancestor,” says senior author Laura Cuaya of the University of Vienna. “With dogs, the story is totally different. They followed a very different evolutionary path, yet through domestication, they developed the social abilities needed to understand and cooperate with us.” 

In this study, the canine participants were all pets from loving families, notes the team. Free-ranging dogs, such as those that live on the street, navigate a very different social world and may process human cues differently. 

Next, the researchers plan to adopt a more dog-centric perspective to understand how dogs integrate these brain signals to make sense of the humans around them. Their future work will also compare how human and dog brains process the same emotional signals. 

“I would like people to see dogs as emotional beings,” says Cuaya. “They have evolved with us to understand our expressions and cooperate with us, and recognizing that can change how we communicate with and care for them.”