Both dogs and humans have dedicated brain areas for voices, and they react in similar ways when processing emotional cues, a new study suggests.
The findings suggest that voice areas evolved at least 100 million years ago, the age of the last common ancestor of humans and dogs.
The study offers new insight into humans' unique connection with our best friends in the animal kingdom and helps explain the behavioural and neural mechanisms that made this alliance so effective for tens of thousands of years.
"Dogs and humans share a similar social environment," said Attila Andics of MTA-ELTE Comparative Ethology Research Group in Hungary.
"Our findings suggest that they also use similar brain mechanisms to process social information. This may support the successfulness of vocal communication between the two species," said Andics.
Andics and colleagues trained 11 dogs to lay motionless in an fMRI brain scanner.
That made it possible to run the same neuroimaging experiment on both dog and human participants - something that had never been done before.
They captured both dogs' and humans' brain activities while the subjects listened to nearly 200 dog and human sounds, ranging from whining or crying to playful barking or laughing.
The images show that dog and human brains include voice areas in similar locations. Not surprisingly, the voice area of dogs responds more strongly to other dogs while that of humans responds more strongly to other humans.
Researchers also noted striking similarities in the ways the dog and human brains process emotionally loaded sounds.
In both species, an area near the primary auditory cortex lit up more with happy sounds than unhappy ones. Andics said the researchers were most struck by the common response to emotion across species.
There were some differences, too: in dogs, 48 per cent of all sound-sensitive brain regions respond more strongly to sounds other than voices.
That's in contrast to humans, in which only 3 per cent of sound-sensitive brain regions show greater response to nonvocal versus vocal sounds.
The study is the first step towards understanding how it is that dogs can be so remarkably good at tuning into the feelings of their human owners.
"This method offers a totally new way of investigating neural processing in dogs. At last we begin to understand how our best friend is looking at us and navigating in our social environment," Andics said.
The study was published in the Cell Press journal Current Biology.
