Dog lovers may have noticed their furry companions are remarkably good at interpreting laughs, frowns and tears.

But scientists have peered inside the brains of dogs from loving families and discovered they really can distinguish between smiles and negative facial expressions, including fear, anger and sadness.

“Humans are really good at picking up small details on the face, and so are dogs,” said study author first Raúl Hernández-Pérez from the University of Vienna.

“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.”

For the study, published in the Cell Press journal, iScience, researchers conducted brain scans of dogs as the canines viewed images of human expressions.

The brain scans revealed that dogs process smiles in a unique brain region and, for the first time, provided evidence that the animals can distinguish between negative facial expressions.

Researchers first tested pictures of happiness on the dogs - an expression that previous studies suggest holds particular significance for dogs.

Eight dogs’ brains were scanned while the researchers showed them images of strangers with either a happy or neutral expression.

The happy faces lit up the temporal cortex and caudate nucleus in the dogs’ brains - regions associated with higher cognitive and reward processing, respectively.

“The activity in the caudate nucleus is particularly interesting,” said Laura Cuaya, also of the University of Vienna, “It suggests that happy human faces may have emotional significance for dogs.”

To find out if the same brain regions responded to other emotions, researchers showed images of people displaying happiness, anger, fear, and sadness to 12 dogs.

Brain scans showed the dogs did not react in the same brain regions meaning dogs respond uniquely to happiness.

A whole brain scan 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.

But this ability does not mean that dogs experience emotions exactly as humans do, researchers say. In real life, 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,” said senior author Laura Cuaya of the University of Vienna. “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.”

However, study authors did note that all the dogs tested were from loving families and dogs that live on the street, navigate a very different social world and may process human cues differently.