Can a familiar smell be enough to give a dog a feeling of well-being, even when their favorite human is away? A study published in the journal Behavioral Processes* reveals that the smell of a person the animal knows triggers a particular response in its brain.
Through this study, the researchers wanted to understand how our 4-legged companions react to human and canine odors, but also to determine whether familiarity plays a role in their brain responses.
To find out, they studied 12 doggies trained to stay still in a functional magnetic resonance imaging (fMRI) machine; a technique for observing variations in brain activity by measuring changes related to blood oxygenation. The animals participated in the sessions without constraints, without anesthesia and without being tied up.
During the test, the scientists presented them with 5 different odors: that of a familiar human, of a stranger, of a dog they knew, of a foreign dog, as well as their own. Note that the adopters were not the people responsible for handling the canines during the exercise. This detail made it possible to verify whether the brain reaction was linked to the smell itself, rather than to the presence of the human or a direct interaction with the latter.
As the article points out, the researchers were interested in the caudate nucleus, a region of the brain associated with reward mechanisms and positive expectations. This circuit is particularly involved in motivation and learning.
A smell associated with a positive experience
The results reveal a clear difference between the 5 odors. All activated the dogs' olfactory system in a comparable way, but only one provoked the most marked response in the caudate nucleus: that of the familiar human.
This means that their brains were not just detecting a biological odor, but were particularly responsive to that of a known person, even when they were not present. For researchers, this brain activity suggests that smell is associated with a positive experience, which may also reflect the importance of the social bond between a doggie and the humans who share its life.
These answers help to understand why a piece of clothing worn by its adopter can interest a dog and why certain familiar smells seem to reassure him in its absence. In addition, they highlight the role of smell in the relationship between an animal and its surroundings, beyond visual and physical contacts.
* “Scent of the familiar: An fMRI study of canine brain responses to familiar and unfamiliar human and dog odors”, Gregory S. Berns, Andrew M. Brooks, Mark Spivak, Behavioral Processes, January 2015.