Every dog owner knows that saying Good dog! in a happy, high-pitched voice will evoke a flurry of joyful tail wagging in their pet.
That made scientists curious: What exactly happens in your dog's brain when it hears praise, and is it similar to the hierarchical way our own brain processes such acoustic information?
When a person gets a compliment, the more primitive, subcortical auditory regions first reacts to the intonation—the emotional force of spoken words. Next, the brain taps the more recently evolved auditory cortex to figure out the meaning of the words, which is learned.
In 2016, a team of scientists discovered that dogs’ brains, like those of humans, compute the intonation and meaning of a word separately—although dogs use their right brain hemisphere to do so, whereas we use our left hemisphere. Still, a mystery remained: Do their brains go through the same steps to process approval?
“It’s an important question, because dogs are a speechless species, yet they respond correctly to our words,” says Attila Andics, a neuroscientist at Eotvos Lorand University in Budapest, Hungary, and co-author of both the previous study and the new one, published this week in the journal Scientific Reports. For instance, some dogs are capable of recognizing thousands of names of individual objects, and can link each name to a specific object.
When the scientists studied scans of the brains of pet dogs, they found that theirs, like ours, process the sounds of spoken words in a hierarchical manner—analyzing first the emotional component with the older region of the brain, the subcortical regions, and then the words’ meaning with the newer part, the cortex. (Read how dogs are more like us than we thought.)
This discovery deepens our understanding of how human language evolved, the authors say. Most strikingly, dogs and humans last shared a common ancestor some 100 million years ago, so it’s likely that “the brains of many mammals respond to vocal sounds in a similar way,” says Andics says.
For their experiments, the Hungarian researchers recruited 12 pet dogs (six border collies, five golden retrievers, and a German shepherd) from homes near Budapest. The researchers trained the canines to willingly enter and lie quietly in a functional magnetic resonance imaging machine, or fMRI, where they listened to a dog trainer speaking known words of praise, such as “clever” and “well done,” as well as unknown, neutral words, such as “if” and “yet.”
The trainer spoke in Hungarian, sometimes uttering the words with an enthusiastic, praising intonation, and at other times, a neutral tone. She also deliberately repeated the words and intonations. The machines scanned the dogs’ brain activity as she spoke. (Read how centuries of breeding have reshaped dog brains.)
At first, auditory regions in both the subcortical and cortical regions of the dogs’ brains showed increased activity as they heard the words.
But when the dogs listened to the same (praise or neutral) intonation repeated numerous times, regardless of knowing the words, the activity level in the older part quickly decreased. This rapid decline suggests that intonation is processed in the more ancient dog brain regions.
Similarly, if they listened to repetitions of known words, the activity level in the newer region of their brains slowly declined—but not when they listened to unknown words. This very slow decline in activity in response to known words suggests that newer brain regions are involved in processing the meaning of words.
The study “suggests that what we say and how we say it are both important to dogs,” David Reby, an ethologist at the University of Sussex, in the United Kingdom, said by email.
“We may infer that from our interactions with dogs, but it is somewhat surprising as dogs do not speak, and their [own] communication system [barking] does not have a clear separation between meaning and intonation.”
Previous studies have shown that many animals, from songbirds to dolphins, use the subcortex to process emotional cues, and the cortex to analyze more complex learned signals—even though they can’t talk. Zebras, for instance, can eavesdrop on the emotions in other herbivore species’ calls to learn if predators are nearby.
It’s likely that human language evolved from such cues, recruiting the same neurological systems to develop speech, notes Terrence Deacon, a neuroanthropologist at the University of California, Berkeley.
And as domesticated animals that have evolved alongside humans for the past 10,000 years, dogs make special use of this ancient ability to process human emotions, Andics adds.
“It helps explain why dogs are so successful at partnering with us”—and at times manipulating us with those soulful eyes.