Dogs can tell if you're scared or sad, not just in a bad mood: World-first brain scan study reveals

What makes a dog slink away from a cranky person, while quietly approaching and leaning against someone who is weeping? Most dog owners have seen this play out, according to an article published on The Conversation — their pets responding, in their own way, to human feelings. Science agrees that dogs have emotions too, and these social skills are thought to underpin how successfully dogs have adapted to living alongside humans, the article notes.

But could a dog actually tell an angry person's face apart from a sad or fearful one? New research published in the journal iScience explored exactly that question, using magnetic resonance imaging (MRI) scans of dogs' brains, and turned up some striking findings, according to The Conversation.

Scanning dogs' brains

Dogs are known to be sensitive to human faces. They look longer at our emotional expressions and sounds compared with neutral ones. What scientists weren't sure of, the article explains, was whether dogs were simply differentiating "good mood" (happy) from "bad mood" (angry, fearful or sad), or whether they were treating these expressions as genuine indicators of distinct emotions.

The study, led by Raúl Hernández-Pérez, a neuroscientist at the University of Vienna, and colleagues, set out to explore that gap using MRI to scan pet dogs' brains while they viewed photographs of human faces, according to The Conversation.

Building on their earlier work, the researchers found evidence that dogs do process images of distinct human emotional expressions differently, the article states.

Different brain regions for different emotions

Using machine learning, the researchers showed that when looking at a dog's whole brain, a different brain region was activated to distinguish between fear and sadness — the right rostral suprasylvian gyrus, to be precise — than the region activated to distinguish between fear and anger, which was in the right mid ectosylvian gyrus and left splenial gyrus, per the report.

Interestingly, the analysis did not detect a difference in the brain areas activated when dogs were shown images of human anger and sadness. Fear stood out distinctly from the other two negative emotions, according to The Conversation.

Why would fear stand out?

This raises an obvious question: why? The Conversation article suggests one possibility is that fear and anger are simply more attention-grabbing than sadness. Other research, it notes, has found that dogs react to fear and anger faster, and with a bigger physical response, such as a raised heart rate — likely because these are the expressions most likely to call for a quick response from dogs to stay safe.

Sadness, by contrast, is less likely to pose any direct threat to dogs living with people, so they may feel less urgency to respond to it. As the article's authors note, some dogs simply don't respond with the heroic, Lassie-style behaviour humans might hope for when in distress.

Small sample, significant first

The numbers involved in this research were small — eight and twelve dogs across the two parts of the study, The Conversation reports. Even so, the article describes this as the first MRI-based proof-of-concept evidence that dog brains can distinguish between two human facial expressions representing distinct negative emotions. It suggests that dogs' neural representation of our emotions goes well beyond a simple good/bad split.

The finding also points to something broader, according to the article: perceiving emotion in others — even across species — isn't handled by a single "emotion centre" in the brain, whether in dogs, humans, or other animal species. Instead, it's spread across a network of regions working together, shaped by the demands of living socially.

A sense-ational result

The study's authors, writing in The Conversation, point out that using still images of human faces is a fairly human-centred way of exploring how dogs interpret our emotional states. Dogs, they note, live in rich sensory worlds, where the scent and sound of our speech also convey emotion and shape how they respond to us.

In fact, the article adds, even wolves that have grown up around people show the same kind of response to the odour of human fear as dogs do. This, the authors write, highlights the importance of learning, as distinct from any evolutionary difference in canid bodies or their inherent responses to people — dogs, and wolves, are learning about us in every single interaction they have with us.

Dogs are adept at watching, smelling and listening to our emotions, learning how these signals predict our behaviour towards them, and using that information to live alongside people harmoniously, according to the article. Returning the favour by learning more about how dogs express their own emotions, the authors write, "seems like the least we can do."