The first study to compare brain scans of non-primates and humans has revealed that both dogs and humans have dedicated brain areas for voices, and they react in similar ways when processing emotional cues.
First author Dr. Attila Andics, of MTA-ELTE Comparative Ethology Research Group in Budapest, and colleagues report their findings in the Cell Press journal Current Biology.
"Although parallel evolution cannot be excluded," write the researchers, the study suggests specialized voice areas in the brain began developing over 100 million years ago, when humans and dogs last shared an ancestor. This is much earlier than expected.
The findings also reveal new clues about mechanisms of brain and behavior that may explain the unique connection that has existed between humans and dogs for tens of thousands of years.
Dr. Andics says the social environment of dogs and humans is similar, and their results show they may also use similar brain mechanisms to process social information, which may explain why the two species make such successful companions.
To conduct their unique experiment, which involved taking the same functional magnetic resonance imaging (fMRI) brain scans of both humans and dogs, the researchers trained 11 dogs to lie still in the scanner.
Dr. Andics says they were interested in finding out, for example, "how do dogs process dog sounds, and how similar it is to the way humans process human sounds."
Same areas in dog and human brains respond to vocal sounds
To conduct their experiment, the researchers trained 11 dogs to lie still in the fMRI scanner.
Image credit: Eniko Kubinyi
While in the scanner, the canine and human participants listened to nearly 200 different vocal sounds of people and dogs, many with emotional connotations, such as whining, crying, laughing and playful barking.
The fMRI images showed that the same areas in the brains of both dogs and humans respond to vocal sounds.
And it came as no surprise to the researchers that the responses were strongest when the participants listened to sounds of their own species.
Plus, when they played vocal sounds loaded with emotional cues, the researchers found striking similarities in the brain responses of both humans and dogs, as they note:
"Our findings also reveal that sensitivity to vocal emotional valence cues engages similarly located non-primary auditory regions in dogs and humans."
For instance, when the participants heard "happy" sounds, in both species, the same part of the brain lit up more than for "unhappy" sounds.
Dog and human brains respond differently to non-vocal sounds
When the participants heard "happy" sounds, the same part of the brain lit up more than for "unhappy" sounds.
Image credit: Borbala Ferenczy
Dr. Andics says they were very struck by these similarities. However, there were also some key differences.
For example, reaction to non-vocal sounds compared with vocal sounds differed greatly between the species.
In dogs, 48% of their sound-sensitive brain regions responded more strongly to non-vocal sounds than vocal sounds, compared with only 3% of sound-sensitive brain regions in humans.
The researchers say the study is a first step in helping understand how our four-legged friends are so good at sensing our feelings.
Dr. Andics says their method offers a completely new approach to looking at dogs' brains and how they work, so we can "begin to understand how our best friend is looking at us and navigating in our social environment."
In August 2013, Medical News Today learned of another intriguing study looking at dogs and humans, where researchers in Japan concluded that owners' yawns are contagious to dogs, and the response is likely empathic, rather than a result of stress.
Should this be confirmed, then the researchers say it is significant because it could become a powerful tool for exploring the root of empathy in animal evolution.