A dog’s brain is odor-sensitive. A new map now reveals the extent of such wiring. According to research published in the Journal of Neuroscience on July 11, strong nerve connections connect the dog’s nose to large portions of the brain. No other animals, including humans, have ever had one of these canine linkages, a substantial link between smell and vision-processing regions.
The findings provide a groundbreaking anatomical explanation of how canines ‘see’ the world using their noses. According to retired army veterinarian and authority on working dogs Eileen Jenkins, the new brain map is ‘excellent, foundational work.’ ‘To say that they have all these same connections that we have in humans, and then some more, it’s going to revolutionize how we understand cognition in dogs.’
According to Pip Johnson, a veterinary radiologist and expert in neuroimaging at Cornell University College of Veterinary Medicine, the findings aren’t entirely unexpected. Dogs are excellent searchers. Compared to humans, who are thought to have 5 million receptors in their noses, these animals’ noses contain between 200 million and 1 billion odour molecule sensors. Additionally, compared to humans, dogs’ olfactory bulbs might be up to 30 times larger. Johnson was interested in how smell information travels to different parts of the brain outside of the obvious sniffing apparatus.
20 mixed-breed dogs and three beagles had MRI scans by Johnson and colleagues in order to create the map. The subjects were all likely good sniffers because they had medium-sized heads and lengthy nostrils. Then, researchers discovered segments of white matter fibres that transmit impulses between brain regions. A method called diffusion tensor imaging, which relies on the movement of water molecules along tissue, revealed the underlying tracts, which Johnson likens to the brain’s ‘road network.’
The olfactory bulb, a brain structure behind the dogs’ eyes, receives odour information when it enters the nose. But it wasn’t immediately obvious where the signals went after that. Johnson was astounded by what she found when she searched for the tracts in the canine MRI data. She claims, ‘I just kept uncovering these enormous paths.’ They appear to be information highways circling back into the brain from the nose.
The olfactory bulb and regions of the brain related to memories and emotions are connected by well-known roads on the new dog brain map. These pathways explain why smelling a scent can take one back in time in people.
Dogs use all their senses to evaluate their environment. But this newfound connection between smell and sight suggests that the two are intricately linked. Perhaps this anatomical link could be why smell can often compensate when a dog’s sight goes, Johnson says. ‘Blind dogs can still play fetch.’
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