Dog owners may know this, but science now has proof that dogs are actually able to tell whether we are happy or unhappy.
Scientists have scanned dogs' brains to reveal how they process a variety of human facial expressions, including happiness, sadness, anger and fear, according to a study published in the scientific journal iScience on Monday.
The scans, conducted by a team from the University of Vienna, showed that dogs' brains respond in different ways depending on the expression on people's faces.
“When we compare humans to primates, we are looking at abilities that we may have inherited from a common ancestor,” Laura Quaya, the lead researcher involved in the study, explained the findings in a press release published on the university’s website.
She added: “With dogs, the story is completely different. They took a very different evolutionary path, however, through domestication, they developed the social capabilities necessary to understand us and cooperate with us.”
The researchers examined the brains of 8 dogs - 6 Border Collies, 1 Labrador, and 1 Golden Retriever - while showing them pictures of strangers with happy or neutral facial expressions.
Images of happy faces led to increased activity in areas of the brain associated with higher cognitive functions and reward processing, specifically the temporal cortex and caudate nucleus.
“This suggests that happy human faces may have an emotional connotation for dogs,” said Cuaya, who began the research at the National Autonomous University of Mexico, then expanded it through a collaboration with Eötvös Lorand University in Hungary before moving to the Austrian capital.
Next, the researchers wanted to see if the same areas of dogs' brains would respond to other emotions. They showed 12 dogs pictures of people showing emotions of happiness, anger, fear or sadness, and used machine learning techniques to analyze their brain activity.
But the dogs' brains did not respond to expressions of anger, fear, and sadness in the same way they did to happiness. However, a comprehensive brain analysis showed distinct patterns of activity when the dogs saw faces expressing these negative emotions.
“Humans are very good at picking up fine details in faces, and so are dogs,” said Raul Hernandez-Pérez, lead author of the study and a researcher at the University of Vienna.
He added: "This is what makes dogs so interesting. By studying their brains, we can understand the adaptations that have evolved to support their remarkable ability to understand humans socially and emotionally."
Kuwaya and Hernandez-Perez are partners in their private and professional lives, and have two dogs, Odin and Kun-Kun, who participated in this study.
"The discovery that the caudate nucleus is involved in processing happy faces was a pleasant surprise," Hernandez-Perez told CNN.
He added: "Across different species, this area of the brain has been associated with reward processing. For dogs specifically, caudate nucleus activity was associated with food rewards, as well as with social rewards, such as hearing words of praise and smelling the scent of a familiar person."
He continued: "Although we cannot directly access dogs' subjective experience, our results suggest that seeing happy faces, even when they are of strangers, involves positive emotional processing."
The team stressed that the way dogs process emotions is more complex than simply looking at a static image of a facial expression, as dogs take into account other signals such as human body language, voice, and smell.
The researchers also pointed out the importance of keeping in mind that all the dogs participating in the study came from homes that provided them with care and love, while dogs living on the streets may deal with human signals in a completely different way.
Hernandez-Perez explained to CNN that the dogs had to be carefully selected and trained to be able to participate in the study.
"The dogs had to be medium sized, mainly due to the dimensions of the MRI machines, and in good health and not have behavioral problems such as an extreme fear of loud noises," he said.
He added: "We first teach the dogs that the task is simply to remain still. We start with just a second or two and then gradually increase the duration. In fact, one of the most challenging parts is getting the idea to the dog that 'doing nothing' is in itself the required task."
"We then gradually introduce the dogs to the different elements of the MRI environment, which includes posture, equipment and the sounds of the scanner. The dogs always participate of their own volition and can leave at any moment," he continued.
But the researchers pointed out that the study has a number of limitations. The number of participating dogs was small, and most of them were Border Collies, known for their intelligence and ability to respond to social signals.
“Border Collies likely have a greater ability to interpret human facial expressions, and future studies are needed to determine whether there are behavioral and brain differences between breeds in the perception of human facial expressions,” the study stated.
Scientists now hope to adopt a more "dog-centred" approach to their research, with the aim of understanding how dogs use these signals to understand humans.
“When we consider how closely dogs pay attention to our emotions, we can also try to become better at recognizing how they express their feelings,” Hernandez-Perez told CNN. “Emotions are a powerful way to communicate, and they can connect us even across species.”
