Scientists have identified what happens inside a dog's brain when it looks at a human face showing different emotions, offering an explanation for why dogs seem so attuned to our moods. Researchers at the University of Vienna found that images of smiling human faces activated the dogs' brain reward circuitry, the region linked to pleasure and motivation, even when the faces belonged to complete strangers. This suggests happy human expressions carry positive value for dogs, shedding light on the neurological basis of the close bond between the two species.

The study involved 14 dogs trained to lie still in a brain scanner while shown photographs of people displaying happiness, anger, fear and sadness; only happy faces triggered the reward response, while the dogs did not appear to distinguish between the different negative emotions. The research was led by Laura Cuaya and Raúl Hernández-Pérez, a Mexican couple who study canine cognition together and used their own border collies, Odín and Kun-kun, as participants alongside dogs recruited from local dog parks. The pair say the findings add to a growing body of evidence showing how thousands of years of domestication have reshaped dogs' brains, giving them a unique capacity to read and cooperate with humans.