A peek inside dogs' brains revealed man's best friend can distinguish emotions ​in people's faces, researchers at the University of Vienna have found, providing what ⁠they said was ⁠the first ever evidence of such an ability.

In the study, researchers used machine learning ​to analyse brain scans of ​12 dogs ⁠as the animals viewed images of human faces displaying different emotions, the university said in a press release on Tuesday.

Researchers found that brain regions linked to higher cognitive functions and reward processing, the temporal cortex and caudate nucleus, were activated only by images of happy strangers.

Anger, fear and sadness did not trigger those regions, according ⁠to ⁠the study, published in Cell Press journal iScience on Monday.

However, when the researchers looked at the whole brain, they found distinct activity patterns that differentiated fear from anger and sadness, providing the first evidence that dogs can tell apart specific negative facial expressions.

Dogs "have evolved with ⁠us to understand our expressions and cooperate with us, and recognizing that can change how we communicate with and ​care for them," senior author Laura Cuaya said.

The researchers ​next plan to investigate how dogs integrate other cues, including body language, voice ⁠nuances ‌and scent, ‌to interpret the humans around them.

They ⁠also hope to compare ‌how human and canine brains process the same emotional signals.

The ​researchers added that ⁠participants in the study were all ⁠pets from loving families and cautioned that ⁠dogs outside such environments ​may respond to human emotional cues differently.