A new brain-imaging study of mankind’s best friend has found a striking similarity in how humans and dogs — and perhaps many other mammals — process voice and emotion.
Like humans, dogs appear to possess brain systems that are devoted to making sense of vocal sounds, and are sensitive to their emotional content. These systems have not previously been described in dogs or any non-primate species, and the new findings offer an intriguing neurobiological glimpse into the richness of our particular corner of the animal kingdom.
“What makes us really excited now is that we’ve discovered these voice areas in the dog brain,” said comparative ethologist Attila Andics of Hungary’s Eötvös Loránd University, lead author of the Feb. 20 Current Biology paper describing the experiments. “It’s not only dogs and humans. We probably share this function with many other mammals.”
Conducted in the laboratory of fellow Eötvös Loránd ethologist Ádám Miklósi, one of the world’s foremost researchers on canine intelligence and behavior, the study was inspired by a turn-of-the-millennium discovery of regions of the human brain attuned to human voices. Similar regions have since been described in monkeys, which last shared a common ancestor with humans 30 million years ago.
'It's not only dogs and humans. We probably share this function with many other mammals.'Humans and dogs last shared a common ancestor 100 million years ago. If a voice-attuned region could be found in dogs too, the trait would truly run deep in our shared biology.
To investigate the possibility, Andics and colleagues trained six golden retrievers and five border collies to lie motionless inside a scanner so the researchers could collect fMRI scans of their brains. These scans measure changes in blood flow, which is widely considered an indicator of neural activity.
Inside the scanner, each of the 11 dogs, and a comparison group of 22 men and women, listened to nearly 200 recordings of dog and human sounds: whining and crying, laughing and barking. As expected, human voice-processing areas responded most to human voices. In dogs, corresponding brain regions responded to the sounds of dogs. In both species, the activity in these regions changed in similar ways in response to the emotional tone of a vocalization — whining versus playful barking in dogs, for instance, or crying versus laughing human voices.
To people who know dogs as companions and friends, the results might seem predictable. But seeing it play out in the brain drives the point home.
“It’s not a surprising finding, but it’s an important finding,” said cognitive ethologist and author Marc Bekoff, who was not involved in the study. Processing vocal sounds and emotion “is fundamental to who they are.”
The responses were not identical between species. In dogs, vocal processing areas also responded to non-vocal sounds, but in humans they were triggered by voice alone — hinting, perhaps, at the intensely social trajectory of human evolution, said Andics. The areas may have evolved to be even more finely tuned for vocal sounds in humans, he speculated. Dogs in the study were also slightly better-attuned to human voices than people were to those of dogs.
That said, what the two species share appears to outweigh the differences, and raise some fascinating questions. Dog intelligence and social awareness is sometimes attributed to the 15,000 or so years they — Canis lupus familiaris, to be precise — have spent in the company of humans, being evolutionarily rewarded for social sensitivity.
The regions tagged in the new study, however, have deep evolutionary roots. Though dogs might conceivably have developed them independently of humans, it’s far more likely that they were present in that long-ago common ancestor, said Andics. They might even be traced further back into our evolutionary heritage.
Neuroscientist Jaak Panksepp of Washington State University, who studies the neurobiology of emotions in animals, said the findings “are to be expected from what we have long known about the overall evolutionary organization of mammalian brains.” Panksepp, who was not involved in the study, believes that sophisticated sound-processing and emotional sensitivity is a fundamental trait of mammals.
Breeding by humans no doubt refined the vocal processing systems of dogs, said Bekoff, but they were likely quite sophisticated by the time our species’ paths converged 15,000 years ago. Certainly wolves, coyotes and other undomesticated members of the canine genus are quite vocal and sensitive to emotion; perhaps that’s why humans and dogs made such a good team.
Neuroscientist Greg Berns of Emory University, the first researcher to study dogs with fMRI, called the new findings “very cool.” The imaging was done well, he said, and the results free of confounding factors that can make brain scans less insightful than they first appear.
Berns did caution, though, that while emotional processing appears to be concentrated where the researchers measured it, it might also occur in other brain regions not examined in this round of scanning. “Their study doesn’t quite answer that, but it’s a first step,” he said. Neither does the new study compare how the two species experience emotion, or the extent to which that’s shaped by other cognitive capacities.
Another open question is what dogs hear when humans speak. The present study didn’t look at that, but the researchers noted earlier observations of common patterns in human and canine vocalizations. When dogs signal positive emotions, their barks come in short bursts, not unlike human laughter; when they’re upset, the barks are deeper and longer, a bit like moans. “There are these acoustic rules that convey emotional information, and they seem to be common to species,” Andics said.
By comparing differences and similarities in human and dog brains, said Andics, scientists might learn more about what gives rise to human language and our sophisticated cognition. By the same token, though, we might find that much of what we consider sophisticated is built from basic mental building blocks found in many other animals.
“These are the questions that are very exciting, and we want to study them further,” he said. Lest dog-lovers worry that mankind’s best friend could be harmed in the excitement of scientific inquiry, Andics emphasized that only dogs who wanted to go inside the scanner took part in the study. “Dogs that didn’t like the procedure stopped coming,” he said.
