Dogs have a sense of smell that is a thousand times better than that of humans! And now a new study has harnessed this incredible sense to reveal the special place an owner has in a dog’s heart!
Researchers have found key regions in a canine brain only light up when the animal is exposed to the smell of a human being that cares for it.
These same regions fail to activate when exposed to other dogs – even familiar ones – according to researchers at Emory University in Georgia.
“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.
Their study, published in the Behavioural Processes, involved training a dozen dogs to remain motionless, while unsedated and unrestrained, in an MRI machine.
- Study trained 12 dogs to remain still without sedation in an MRI scanner
- It looked at brain region named the caudate which is linked to rewards
- In a dog brain, caudate is uniquely activated by scent of a familiar human
- Region fails to activate when exposed to other dogs – even familiar ones
- The research builds on a previous study which found dogs use the same part of the brain as humans to ‘feel’
A human nose has six million sensory receptor sites, a sheepdog’s nose has 200 million and a beagle’s nose has 300 million. Next to them, we humans smell almost nothing. While humans don’t spend a lot of time thinking about our sense of smell, a dog does. Its sniff begins with muscles in the nostrils straining to draw a current of air into them.
At the same time, the air already in the nose is pushed deeper inside or off through slits in the side, pulling yet more of the new scent in. This action is markedly different from human sniffing, with its ‘in through one nostril hole, out through the same hole’ method.
Dogs are continually refreshing the scent in their nose, as though shifting their gaze to get a better look.
The researchers where then able to look at two areas of the dogs’ brains: the ‘olfactory bulb,’ which indicates the animal’s sense of smell has been activated, and the caudate.
Previous studies show that the caudate in other mammals, including humans, points to this region’s role in processing positive expectations such as social rewards.
While remaining motionless in the MRI scanner for around half an hour, the 12 dogs were exposed to five different smells. The smells 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 researchers found the olfactory bulb ‘was activated to a similar degree’ when the dog was exposed to each scent. But the smell of the familiar human activated the caudate far more noticeably.
“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.”
Professor Berns, however, added that they cannot be sure whether it’s the person who activates this positive response, or the person’s actions, such as offering the dog food. “Although possible, we think this unlikely”, the researchers write, “because most of the familiar humans were not the dogs’ primary caregivers.” The research adds to a previous study by the same group that found dogs use the same part of the brain as humans to ‘feel’.
Professor Berns there was a striking similarity between dogs and humans in both the structure and function of a key brain region: the caudate nucleus. The caudate sits between the brainstem and the cortex and is rich in dopamine receptors. In dogs, the research found that activity in the caudate increased in response to hand signals indicating food.
“Do these findings prove that dogs love us? Not quite. But many of the same things that activate the human caudate, which are associated with positive emotions, also activate the dog caudate,” said Berns. Neuroscientists call this a functional homology, and it may be an indication of canine emotions.
The ability to experience positive emotions, like love and attachment, would mean that dogs have a level of sentience comparable to that of a human child!