Dogs fondly remember us — even our B.O. — when we’re not around, suggests a new study on how dogs respond to the scent of a familiar human.

The research, published in the latest issue of Behavioral Processes, was the first brain-imaging study of dogs as they responded to smells of other dogs and people.

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“It’s one thing when you come home and your dog sees you and jumps on you and licks you and knows that good things are about to happen,” project leader Gregory Berns said in a press release.

“In our experiment, however, the scent donors were not physically present. That means the canine brain responses were being triggered by something distant in space and time.”

When we smell the perfume or cologne of someone we love, the reaction may be immediate and emotional and not necessarily at a conscious level, Berns, who is director of the Center for Neuropolicy at Emory University, added. “Our experiment may be showing the same process in dogs. But since dogs are so much more olfactory than humans, their responses would likely be even more powerful than the ones we might have.”

If you have a dog, your unique smell could very well be the best thing that your dog has ever whiffed.

The study involved 12 dogs of various breeds. The animals had all undergone training to hold perfectly still while undergoing an fMRI scan (probably the hardest part of this study).

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As the dogs were being scanned, they were presented with five different scent samples from the following five sources: the dog itself, an unfamiliar canine, a familiar canine that lived in the dog’s home, an unfamiliar person, and a person who lived in the dog’s household. The latter wasn’t the owner because those people had to serve as handlers throughout the experiment, and the researchers didn’t want the scents to come from a dog or person that would be present in the same room as the experiment was taking place.

Here’s the rather gross part. The dog scents were swabbed from the rear/genital area and the human scents were taken from armpits. This bothered the people more than the dogs, though.

“Most of the dog owners and handlers involved in the experiment were women, so most of the familiar human scent donors were their husbands,” Berns says. “We requested they not bathe or use deodorant for 24 hours before taking the sample. Nobody was too happy about that.”

The results showed that all five scents elicited a similar response in parts of the dogs’ brains (the olfactory bulb and peduncle) involved in detecting smells. The responses, however, were significantly stronger for the scents of familiar humans, followed by that of familiar dogs. Canines that had received training as service/therapy dogs displayed the most positive reactions to the human smells, perhaps due to genetics or because the connection to people had been fostered through more training.

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Berns said that the reactions to familiar people “suggested that not only did the dogs discriminate the familiar human scent from the others, they had a positive association with it. While we might expect that dogs should be highly tuned to the smell of other dogs, it seems that the ‘reward response’ is reserved for their humans. Whether this is based on food, play, innate genetic predisposition or something else remains an area for future investigation.”

Some might just happy to know that dogs pay attention to us and likely think well of us, even our stinky unique scent, when we are away. The scientists, though, have further research goals in mind.

“In addition to serving as companion animals for wounded veterans, dogs play many important roles in military operations,” Berns said. “By understanding how dogs’ brains work, we hope to find better methods to select and train them for these roles.”

Image: A dog’s nose remembers you best. Credit: iStockPhoto