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Dogs know when humans are happy—and it shows in their brains
Dogs are known to recognize and respond to human facial expressions, but a new study shows how deeply they understand our mood
Dogs really do know when their owner thinks they have been a good boy or a naughty pup. Our canine companions can recognize and tell the difference between human facial expressions—and their brains get particularly active when people look happy, a new study shows.
Researchers scanned dogs' brains while the pooches looked at images of human facial expressions depicting happiness, sadness, anger and fear. Different facial expressions—particularly happiness—sparked distinct activity in different parts of the brain, suggesting that at the neurobiological level, dogs can read a range of emotions on our faces.
In one experiment, the researchers trained eight dogs to sit completely still—not moving more than three millimeters—for six minutes in a fMRI machine, all while the dogs wore headphones to protect their ears. The researchers then showed the dogs strangers' faces with either a happy or neutral expression and analyzed their brain activity.
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Distinct parts of the brain lit up when the dogs looked at happy faces, including the caudate nucleus , a region thought to be involved in reward processing, says Laura Cuaya, the paper's senior author and a postdoctoral researcher at the University of Vienna. The same region lights up when a dog smells a familiar person or anticipates a treat, she adds.
Next, the researchers homed in on whether this region of the dog brain is involved in processing happiness or simply all emotions.
In a second experiment involving 12 dogs, Cuaya and her colleagues showed the canines a mix of faces expressing happiness, sadness, anger and fear. The dogs showed a stronger response to happiness compared to other emotions. The researchers also detected differences in the brain activity associated with faces showing fear versus anger or sadness.
"For the first time—and this was exciting—we found this distinction in the dog brain between two negative emotions," Cuaya says. Interestingly, they did not detect a difference in brain activity between anger and sadness. It's unclear why.
"This novel, ground-breaking study demonstrates that the dog brain does not just differentiate emotional valence, such as positive versus negative or good versus bad emotions, but can also process differently between at least some emotion categories, for example, fearful versus angry, much like the human brain does," says Kun Guo, a professor of cognitive neuroscience at the University of Lincoln, in England, who was not involved in the study.
The findings are likely no surprise to dog owners—and they fit with the fact that we've evolved and lived alongside dogs for tens of thousands of years. Dogs have to understand the signals we give them to make that relationship possible, says Raúl Hernández-Pérez, the study's lead author and a postdoctoral researcher at the University of Vienna.
The research has some caveats, Cuaya says. Just because a dog recognizes a happy human face, that doesn't necessarily mean they're happy. It's not possible to know the dogs' "subjective experience," she says.
It's also unclear how much of dogs' ability to differentiate facial expressions is innate, and how much is to do with each dog's experience and learning over time. The dogs in the study came from "lovely families," according to Cuaya, and it's possible they weren't as familiar with negative emotions such as anger.
Plus, the dogs were looking at strangers' faces. Cuaya and Hernández-Pérez expect that pets would be even more sensitive to familiar faces.
"Dogs do pay attention to you, [they] do pay attention to your face. Just by smiling at them, you are giving them something," Hernández-Pérez says. "You're provoking a small response in the brain related to reward processing—just by smiling."
The research was published on Monday in the journal iScience.
Jackie Flynn Mogensen is a breaking news reporter at Scientific American . Before joining SciAm, she was a science reporter at Mother Jones, where she received a National Academies Eric and Wendy Schmidt Award for Excellence in Science Communications in 2024. Mogensen holds a master's degree in environmental communication and a bachelor's degree in earth sciences from Stanford University. She is based in New York City.
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