Who Loves His Master? Brain Scans Provide Clues to a Dog's Inner Life - Pacific Standard

Who Loves His Master? Brain Scans Provide Clues to a Dog's Inner Life

New research suggests a region of a canine brain that is associated with rewards is uniquely activated by the scent of a familiar human.
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(Photo: Annette Shaff/Shutterstock)

(Photo: Annette Shaff/Shutterstock)

Do you ever wonder where your dog’s true loyalty lies? Sure, you two are close. But as their urine smell-based information network regularly reminds us, canines communicate with their peers on a level we can’t possibly understand. So what takes precedence in a dog’s mind: His species, or his master?

Newly published research provides evidence that points to the primacy of a dog’s human handlers.

A first-of-its-kind study that measured activity in dogs’ brains finds a key region only lights up when the animal is exposed to the smell of a familiar human being. Other dogs—even familiar ones—do not produce the same response.

“It is tempting to conclude that (this) response represents something akin to a positive emotional response to the scent of a familiar human,” writes the research team led by Gregory Berns of Emory University. Their study—including their speculative discussion of whether that’s truly the case—is in the journal Behavioural Processes.

A first-of-its-kind study that measured activity in dogs’ brains finds a key region only lights up when the animal is exposed to the smell of a familiar human being. Other dogs—even familiar ones—do not produce the same response.

Berns and his colleagues trained a dozen dogs “to remain motionless while unsedated and unrestrained” in an MRI machine—the same device used to determine what parts of the human brain are activated when certain activities are thought about or performed.

The researchers specifically looked at two areas of the dogs’ brains: the “olfactory bulb,” which indicates the animal’s sense of smell has been activated, and the caudate. “A vast literature on the caudate in humans, monkeys, and rats points to this region’s role in positive expectations, including social rewards,” they note.

While standing or sitting quietly in the brain-scanning device for about a half-hour (good dogs!), the 12 canines were exposed to five distinct smells, all collected that same morning on sterile gauze pads. The odors were from the dog itself; a different dog who resided in the same household; an unfamiliar dog; a familiar human; and a human the dog had never met.

The familiar human was either a member of the dog’s household or a close friend (but not the person handling the animal that day). For 11 of the 12 animals, it was “either the handler’s husband or their child.”

The researchers found the olfactory bulb “was activated to a similar degree” when the dog was exposed to each scent. Crucially, however, the smell of the familiar human led to the greatest activation of the caudate. Responses to the other four scents did not significantly differ from one another.

This suggests that “not only did the dogs discriminate that scent from the others—they had a positive association with it,” the researchers write. “This speaks to the power of the dog’s sense of smell, and it provides clues about the importance of humans in dogs’ lives.”

Berns and his colleagues note that the caudate is associated with positive emotions, but they can’t be sure that is an accurate description of the dog’s experience. They note caudate activation could indicate a “motivational state”—specifically, “a marker to approach the stimulus,” which in this case would be a desire to make contact with the person in question.

Of course, the easiest way for a human to pique a dog’s interest is to offer it food. This raises the possibility that the brain response noted here simply reflects the fact the dog associates the smell of this person with dinner.

“Although possible, we think this unlikely,” the researchers write, “because most of the familiar humans were not the dogs’ primary caregivers. Most of the handlers reported that they were the ones who fed the dog.” The person who provided the scent played with the dog, perhaps took it for walks, but seldom fed it.

Berns and his colleagues don’t know whether this human-centric response is the result of selective breeding, or perhaps socialization. (All 12 dogs were raised from puppies as family pets, and four were service animals.)

Regardless, they write, this research suggests dogs uniquely associate their humans with rewards, and act accordingly. Whether to call that “love” is a subjective decision.

There’s no question, however, that in your dog’s eyes, you are very special.

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