Scent of my human

The functional MRI research team led by Gregory Berns have done it again. In research published in the journal Behavioural Processes, they show that an area of the canine brain associated with reward responds more strongly to the scents of familiar humans than it does to the scents of other humans, or even to those of familiar dogs.

Kady, a lab involved in the study, shown training for the experiment in a mock-up fMRI scanner. Photo by Helen Berns

“In our experiment, the scent donors were not physically present. That means the canine brain responses were being triggered by something distant in space and time. It shows that dogs’ brains have these mental representations of us that persist when we’re not there.”

When humans smell the perfume or cologne of someone they love, they may have an immediate, emotional reaction that’s not necessarily cognitive, Berns notes. “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.”

The experiment involved 12 dogs of various breeds. The animals had all undergone training to hold perfectly still while undergoing an fMRI scan. As they were being scanned, the subjects were presented with five different scents that had been collected on sterile gauze pads that morning and sealed in Mylar envelopes. The scent samples came from the subject itself, a dog the subject had never met, a dog that lived in the subject’s household, a human the dog had never met, and a human that lived in the subject’s household.

The familiar human scent samples were taken from someone else from the house other than the handlers during the experiment, so that none of the scent donors were physically present.

The dog scents were swabbed from the rear/genital area and the human scents were taken from armpits.

The results showed that all five scents elicited a similar response in parts of the dogs’ brains involved in detecting smells, the olfactory bulb and peduncle. The caudate responses, however, were significantly stronger for the scents of familiar humans, followed by that of familiar dogs.

“The stronger caudate activation suggested that not only did the dogs discriminate the familiar human scent from the others, they had a positive association with it,” Berns says. “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.”

An interesting twist: The dogs in the experiment that had received training as service/therapy dogs showed greater caudate activation for the scent of a familiar human compared with the other dogs. It is unclear whether this difference was due to genetics or had simply been fostered through the service/therapy training.

“We plan to do further research to determine whether we can use brain-imaging techniques to better identify dogs that are optimal to serve as companion animals for the disabled,” Berns says.

The training of service dogs is time-consuming and expensive, he says, and only about one-third of the animals that begin the process successfully complete it. Meanwhile, the waiting list for service dogs is long, and includes many wounded veterans.

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

Source: Emory University media release

Read my other blogs about functional MRI research: