As any dedicated dog owner will tell you, canines often appear to grasp the emotional content of what's being said to them. An unprecedented brain scanning study now shows this is likely true — and that this capability pre-dates domestication.
This is not the first time dogs have been studied in an MRI scanner. Last year, neuroeconomics professor Gregory Burns analyzed the canine caudate nucleus — a key brain region shared by humans and dogs, and one that's associated with the anticipation of things we enjoy, like food, love, and material things. Burns's scans led him to conclude that dogs are as conscious as human children.
Other studies have demonstrated the emotional richness of the canine inner life. Dogs can express their emotions through tail wagging (dogs wag to the right when they're happy, and to the left when they're stressed or anxious), and they also respond emotionally to the tail wagging of other dogs. On the other side of things, studies have also shown that humans can distinguish between a dog's happy and sad barks.
Now, we know that dogs can understand language. But what's a bit uncertain, apart from what we see in behavioral studies, is whether or not dogs can comprehend the underlying emotional tone of what's being said to them. An experiment conducted by lead researcher Attila Andics from the Hungarian Academy of Science's Eotvos Lorand University in Budapest sought an answer to that very question.
The new study, the details of which now appear in Current Biology, is the first to perform a comparative neurological analysis of humans and a non-primate species. After extensive training (12 sessions) and a generous diet of positive reinforcement, 11 dogs were readied for the experiment. The dogs were trained to lie completely still for as long as eight minutes at a time (subjects must remain completely motionless in an MRI scanner for it to work properly). The dogs were given headphones to both muffle the loud, whining noises emanating from the scanner (it can reach 95 decibels), and to provide the 200 individual sounds required for the experiment.
Photo: Eniko Kubinyi.
The sounds were used to tickle parts of the dogs' auditory cortex — the part of the brain responsible for processing acoustic information. Various sounds included environmental noises, like car sounds and whistles, human sounds (but not words), and dog vocalizations (like barking and growling).
Likewise, 22 humans were brain scanned as they listened to the exact same sounds.
Analysis of the scans showed that the temporal pole (a.k.a. Brodmann area 38) — the most anterior region of the temporal lobe — lit up when both dogs and humans heard human voices.
This part of the brain — previously thought unique to humans — is thought to process incoming sounds, giving rise to emotional responses. In humans, this area becomes active when voices are heard. But now it appears that it becomes active in dogs as well — the first time scientists have observed this in a non-primate.
At the same time, emotional human sounds, like crying and laughing, activated an area near the primary auditory cortex in both species. Emotionally charged dog vocalizations (such as whimpering or angry barking) caused similar reactions among all volunteers.
The results of this study strongly suggest that dogs are very good at tuning into the feelings of their owners. That said, dogs reacted more strongly to canine sounds than human sounds, and they paid more attention to extraneous noises (like the environmental sounds). In fact, about half of the entire auditory cortex lit up in dogs when listening to these sounds, compared to just 3% of the same area in humans. This could mean one of two things, or both — that dogs are less "hardwired" to process human sounds, or that humans are more inclined to process human vocalizations while selectively disregarding peripheral auditory information (also, humans are more "trained" and accustomed to these noises; we don't get as excited or nervous about them as dogs do).
From an evolutionary perspective, the authors write that, "Although parallel evolution cannot be excluded, our findings suggest that voice areas may have a more ancient evolutionary origin than previously known." So, it's possible that dogs and humans, over the course of the past 18,000-to-32,000 years, have been evolving together, and that's why dogs (in particular) are capable of processing the emotions embedded within human vocalizations. But, given that these parts of the brain are far more ancient than that, it's more likely that they emerged in a common ancestor. The researchers speculate that they likely evolved at least 100 million years ago, when humans and dogs last shared a common ancestor — an insectivore.
Read the entire study at Current Biology: "Voice-Sensitive Regions in the Dog and Human Brain Are Revealed by Comparative fMRI."