Dogs may understand far more about our emotions than we realize, according to new brain-scan research.
It’s something dog owners have long suspected: Our four-legged companions seem to know when we’re happy, upset or afraid. Now, scientists say they have found evidence in dogs’ brains that may explain just how they do it.
Researchers from the University of Vienna scanned dogs’ brains while showing them images of human faces displaying different emotions, including happiness, sadness, anger and fear. The findings, published in the journal iScience, suggest that dogs process human facial expressions in distinct ways.
The research found that happy human faces triggered increased activity in areas of the dogs’ brains linked to higher-level cognitive processing and rewards, including the temporal cortex and caudate nucleus.
Lead researcher Laura Cuaya said the findings highlight the remarkable social abilities dogs developed during domestication.
Unlike humans and other primates, dogs did not evolve along the same path as us. Yet thousands of years of living alongside humans appear to have helped them develop sophisticated ways of understanding and cooperating with people.
In one part of the study, researchers scanned eight dogs — six border collies, a Labrador and a golden retriever — as they looked at photographs of strangers with either happy or neutral expressions.
The stronger brain response to happy faces suggested that positive human expressions may carry emotional significance for dogs.
The researchers then expanded the experiment to 12 dogs, showing them faces expressing happiness, anger, fear and sadness. Using machine-learning techniques, they found that the dogs' brains produced different activity patterns when they viewed the various negative emotions.
The response was not identical to the reaction triggered by happy faces, but the whole brain showed recognizable patterns associated with anger, fear and sadness.
“Humans are really good at picking up small details on the face, so are dogs,” said study co-author Raúl Hernández-Pérez. He said studying dogs’ brains could help scientists understand the adaptations that allow them to communicate so effectively with humans.
One particularly interesting finding involved the caudate nucleus, a brain region associated with reward processing across several species.
In dogs, activity in this region has previously been linked not only to food rewards but also to social experiences, such as hearing praise or detecting the scent of a familiar person.
The researchers said their findings suggest that seeing a happy human face — even that of a stranger — may trigger positive emotional processing in dogs.
But dogs don't rely on facial expressions alone.
Their understanding of human emotions is likely influenced by a combination of facial expressions, body language, tone of voice and scent. The researchers also cautioned that the dogs in the study all came from loving homes, meaning dogs living on the streets or with very different experiences may respond to human emotional cues differently.
Getting the dogs into an MRI scanner was another challenge.
The participating dogs had to be healthy, medium-sized and comfortable around loud noises. They were carefully trained to remain still, beginning with just a few seconds and gradually increasing the amount of time.
The dogs were also introduced slowly to the MRI environment, including the equipment, positioning and scanner sounds. Importantly, researchers said the dogs participated voluntarily and could leave at any time.
The study does have limitations. Only a small number of dogs were examined, and most were border collies — a breed particularly well known for responding to human social cues.
That raises the possibility that breed could influence how strongly dogs interpret human facial expressions. More research will be needed to determine whether different breeds show different patterns of brain activity.
The researchers now want to take what they call a more “dogcentric” approach to understanding how canines interpret the many signals humans send them.
And the discovery could go both ways.
By learning more about how closely dogs watch our emotions, scientists say humans may also become better at recognizing the ways dogs communicate their own feelings.
After all, your dog may have been reading your face long before scientists started scanning its brain.