If you’re a dog owner, you may have had the feeling that your dog knows exactly how you’re feeling.
A smile might bring an enthusiastic tail wag, while a frustrated expression can be met with a noticeably different response. But how much information can dogs actually gather just by looking at our faces?
New research suggests the answer may be: quite a lot.
A new study published in iScience used functional magnetic resonance imaging (fMRI) to examine what happens inside dogs’ brains as they view different human facial expressions.
The researchers found evidence that dogs not only respond differently to happy faces, but may also be capable of distinguishing between certain negative emotional expressions—including fear, anger and sadness.
Looking Inside the Canine Brain
Scientists have known for some time that dogs are remarkably sensitive to human social signals.
Previous research has shown that dogs can distinguish between happy and angry human faces, and Humintell has previously explored research showing that dogs examine the eyes when deciphering facial expressions.
The new research takes this a step further by looking directly at how the canine brain responds.
Researchers at the University of Vienna trained family dogs to remain awake and completely still inside an fMRI scanner while looking at photographs of unfamiliar human faces.
In one experiment, dogs viewed happy and neutral expressions. In another, they viewed faces displaying happiness, fear, anger and sadness.
The researchers then compared patterns of brain activity associated with the different expressions.
A Human Smile May Actually Be Rewarding to Your Dog
One of the clearest findings involved happiness.
When dogs looked at happy human faces, researchers observed increased activity in brain areas that included the caudate nucleus, a region associated with reward processing.
This same general reward system can become active when dogs anticipate something positive, such as food, or encounter cues associated with familiar people.
In other words, a human smile isn’t simply something a dog visually notices. The dog’s brain appears to process it in a way associated with reward.
As study lead author Raúl Hernández-Pérez explained, simply smiling at a dog can provoke a small response in the animal’s brain related to reward processing.
Can Dogs Tell the Difference Between Fear, Anger and Sadness?
Perhaps the most intriguing finding involved negative expressions.
Earlier research had already suggested that dogs can discriminate between broadly positive and negative human facial expressions. But could they make finer distinctions within negative emotions?
The new findings suggest that, at least in some cases, they can.
The researchers detected different patterns of brain activity when dogs viewed fearful faces compared with angry or sad faces.
Notably, however, the researchers did not find a clear neural distinction between anger and sadness.
This distinction is important. The study does not demonstrate that dogs understand human emotions in exactly the same conceptual way humans do. Rather, it provides evidence that the canine brain is sensitive to differences among at least some categories of human emotional facial expressions.
According to the researchers, this is the first evidence that dogs’ brains can differentiate between specific negative emotional expressions rather than simply sorting expressions into “positive” and “negative.”
Your Dog Doesn’t Need to Know the Person
Another interesting element of the research is that the dogs weren’t looking at their owners.
They were shown unfamiliar human faces.
That suggests the responses weren’t simply the result of a dog learning that a particular expression on its owner’s face predicts a walk, treat, scolding or belly rub.
The facial expression itself appears to carry meaningful information.
The researchers actually suspect dogs might show even greater sensitivity when looking at people they know well, although that remains to be tested.
Thousands of Years of Learning to Read Humans
Why are dogs so good at paying attention to us?
Domestication may be part of the answer.
Humans and dogs have lived alongside one another for thousands of years. During that time, the ability to detect and respond appropriately to human social signals would have been extraordinarily useful.
Interestingly, communication between humans and dogs appears to have evolved in both directions.
Humintell previously covered research suggesting that domestication changed dogs’ anatomy and behavior in ways that made them better communicators with humans. Their expressive eyebrows, for example, help produce the irresistible puppy-dog eyes.
We’ve also discussed research examining why dogs wag their tails so much more than wolves. One hypothesis is that humans consciously or unconsciously selected dogs for communicative behaviors we found appealing during domestication.
Dogs may therefore have become particularly good at communicating with us—while simultaneously becoming particularly attentive to the signals we send them.
Humans Communicate Differently With Dogs, Too
The relationship gets even more interesting when we look at our own behavior.
As we previously discussed in research on the way humans “baby talk” to dogs, people often use a high-pitched, affectionate tone when speaking to dogs that resembles the way adults speak to babies.
Curiously, however, we don’t necessarily accompany that voice with the same exaggerated facial expressions we use with human infants.
That raises an interesting question in light of the new research: If dogs are paying close attention to our faces, how much information are we communicating to them without realizing it?
Potentially quite a bit.
Don’t Assume Your Dog “Feels” Your Emotion
There is an important caveat to the new findings.
Seeing that a dog’s brain differentiates between human emotional expressions doesn’t tell us exactly what the dog is experiencing internally.
A dog’s brain responding to a happy face does not necessarily mean the dog itself becomes “happy” in the same sense that we would use the word to describe a human emotional experience.
Similarly, recognizing differences between fearful and angry faces doesn’t necessarily mean dogs understand the abstract concepts of *fear* and *anger*.
The researchers also don’t yet know how much of this ability is innate and how much dogs learn through their extensive interactions with people.
Those are important questions for future research.
The Remarkable Nonverbal Relationship Between Humans and Dogs
What makes the findings especially fascinating is that the human-dog relationship exists largely without shared language.
Dogs watch our eyes, faces, bodies, gestures and movements. Humans, in turn, learn to interpret canine signals ranging from facial movements and posture to vocalizations and tail wagging.
Research highlighted previously by Humintell has even suggested that humans can recognize emotional information in dogs’ facial expressions.
The communication, in other words, goes both ways.
The new findings add another piece to that puzzle. Dogs aren’t simply reacting to obvious behaviors such as reaching for a leash or opening a bag of treats. Their brains appear capable of extracting surprisingly nuanced information from the human face itself.
So the next time you look down and find your dog staring intently back at you, remember:
You may be reading your dog’s face—but your dog may be reading yours, too.
Read the Research
The new study, Dog brain representations of human facial expressions: Encoding happiness and differentiating specific negative expressions, was published in iScience.
Additional coverage is available from Science News and Scientific American.