Dogs are animals that understand the emotions of the people they live with. It is not simply a matter of knowing whether someone is in a good or bad mood. They distinguish even among types of negative emotions. Scientists have for the first time identified how a dog's brain responds to human emotions.
A team led by Raúl Hernández-Pérez, a professor in the Department of Psychology at the University of Vienna, said in the international journal iScience on the 10th that "pet dogs process smiles in a specific region of the brain and also distinguish among types of negative facial expressions."
Earlier studies found that dogs can distinguish human facial expressions, but most tested only positive or negative faces. It was unclear whether dogs could distinguish among various types of happy expressions or unhappy expressions.
◇ Positive expressions respond in the reward circuit
The team scanned pet dogs' brains with functional magnetic resonance imaging (fMRI). When a specific brain region works, blood rushes to that area. fMRI shows that region as if a light has been turned on. Using fMRI means researchers can confirm at the brain level how dogs respond to human faces.
While in an fMRI scanner, dogs looked at photos of people showing various facial expressions. In the first experiment, eight dogs were alternately shown photos of unfamiliar people with happy expressions or neutral expressions, and their brain activity was scanned with fMRI. When they saw a happy face, the right temporal lobe and the caudate nucleus in the dog's brain were activated.
The temporal lobe near the ears and temples is a region that processes information, stores memories, and regulates emotions. The caudate nucleus deep in the cerebrum is linked to the reward circuit. Laura Cuaya, a co-corresponding author of the paper, said, "This region's response suggests the dog is processing something positive."
In a second experiment, 12 dogs were shown photos of people expressing happiness, anger, fear, and sadness, and an artificial intelligence (AI) system analyzed whole-brain responses. Dogs' brains distinguished happy expressions from the three negative ones with 60.9% to 69.8% accuracy. Again, happy expressions elicited responses in the right temporal lobe and caudate network.
Bridget Waller of Nottingham Trent University said, "Because the smile is the expression humans most commonly use and is essential to social interaction, it is reasonable to suggest that dogs developed the ability to distinguish it from other expressions as they became domesticated by humans."
◇ Distinguishing even types of negative emotions
Surprisingly, dogs distinguished fearful faces from angry or sad faces. Looking only at specific brain regions did not reveal that difference, but when AI analyzed the overall pattern of brain activity, it did. Hernández-Pérez said, "Different negative expressions may signal different types of threat and therefore trigger different responses."
The researchers estimated that fear might induce facial expressions in humans that are salient enough for dogs to recognize. In fact, prior work found that when dogs viewed faces showing fear or neutrality, they focused their gaze on the nose region. Rather than recognizing a human-like category of fear, it may be that the visual and behavioral cues contained in fearful faces drew dogs' attention relatively more.
By contrast, sadness and anger were not clearly differentiated in whole-brain activity. The team inferred that the face alone did not provide enough information for dogs to distinguish anger from sadness. Prior research showed that dogs observe bodies more than faces when judging human emotions. As in this study, seeing only the face makes it difficult to tell whether someone is sad or angry.
This study is the first to confirm with fMRI and AI machine learning that a dog's brain not only distinguishes good and bad expressions, but also processes fear differently from anger and sadness among negative expressions. However, the sample size was small, and most dogs were border collies, which is a limitation. Even so, the study has practical implications. Cuaya said, "Smiling when training dogs may help the learning process."
References
iScience (2026), DOI: https://doi.org/10.1016/j.isci.2026.116900