New Delhi: A study has found unique brain regions which dogs use to process each emotion, including happiness, and provided first evidence that the canines can distinguish between negative facial expressions, such as anger, sadness and fear.
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The findings, published in the journal iScience, show that faces of happy humans triggers activity in a dog's caudate nucleus, suggesting an emotional significance for dogs.
Researchers peered inside the brains of dogs as they viewed images of various human expressions.
"Humans are really good at picking up small details on the face, and so are dogs. 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," first author Raúl Hernández-Pérez, from the University of Vienna, said.
Brains of eight dogs were scanned as they were showed images of strangers with either happy or neutral expressions.
Happiness -- which previous studies have shown to be significant for dogs -- on the strangers' faces was found to light up the temporal cortex and caudate nucleus in the dogs' brains. The regions are associated with higher cognitive and reward processing, respectively.
"The activity in the caudate nucleus is particularly interesting. It suggests that happy human faces may have (an) emotional significance for dogs," senior author Laura Cuaya, also of the University of Vienna, said.
Twelve dogs, who were shown images of people expressing happiness, anger, fear, and sadness, did not react in the same manner to the negative emotions.
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.
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"Whole-brain representational similarity analyses revealed activity patterns differentiating angry vs. fearful faces (right mid ectosylvian and left splenial gyri) and sad vs. fearful faces (right rostral suprasylvian gyrus) but not angry vs. sad faces," the authors wrote.
"This provides direct evidence that dog brains can distinguish between two negative facial expressions," they said.
The researchers said that the results do not show that dogs experience emotions exactly as humans do.
Further, 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," Cuaya said.
"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," the senior author said.
