(ORDO NEWS) — We all know that dogs have a powerful sense of smell, from sniffing out diabetes, cancer, and positive COVID-19 test results to a disgusting interest in poop. However, the researchers were surprised to see just how extensive the smell wiring is in the dog’s brain.
Cornell University veterinary neuroimaging researcher Erika Andrews and her colleagues have just mapped the olfactory pathways of the brain of domestic dogs (Canis familiaris) using diffusion MRI. This method uses differences in the flow of molecules, such as water, to create a complex map of tissue structures.
Using the data, the team built 3D maps of the dog’s brain pathways and traced the vast white matter that connects the olfactory regions of the brain, revealing a huge, previously unknown information highway between the olfactory and visual systems of dogs.
“We’ve never seen such a connection between the nose and the occipital lobe, which is functionally the visual cortex in dogs, in any species,” explains Cornell University neuroimaging researcher Pip Johnson.
“It was really consistent. And in terms of size, these tracts were really impressive compared to what is described in the human olfactory system, and more similar to what can be seen in our visual system.”
This is probably what allows our smart canine friends to function perfectly even without sight. For example, blind dogs can play ball.
“It’s amazing,” retired military veterinarian Eileen Jenkin, who was not involved in the study, told Laura Sanders of Science News.
“Many people have assumed that such a link exists based on the behavior of trained dogs and detection dogs, but no one has been able to prove it.”
The dog’s nose itself is impressively equipped, with over 220 million odor-detecting cells compared to our 50 million or so olfactory receptors (at last count).
With this sense of smell alone, dogs can form spatial perceptions, read chemical messages, sense our moods, and track all sorts of things, including faint heat sources. So all those extra connections really matter.
“In dogs, it makes a lot of sense,” says Johnson. “When we enter a room, we first of all use our sight to determine where the door is, who is in the room, where the table is.
“While in dogs, this study shows that the sense of smell is indeed integrated with vision in terms of how they learn about and navigate their surroundings.”
Among the 23 dogs scanned, the researchers also identified white matter information pathways that tightly connect the olfactory bulb (bottom left) to four other areas of the brain.
As in humans, olfactory pathways to the piriform cortex (green) and limbic system (blue) likely link smell to memory and emotion. The entorhinal cortex (pink pathway) is believed to process odors and is also associated with memory.
In addition to connections to vision, an unexpected finding was connections between the olfactory bulb and the brainstem via the corticospinal tract (turquoise). These connections could allow for more instinctive responses to smells without involving higher brain regions, Andrews and his colleagues suspect.
The researchers dissected two canine brains to confirm what they saw in the imaging models.
However, they caution that before we can say exactly what these physical connections mean, we need to do electrophysiological studies rather than speculate based on what we know about these brain regions in other species.
And of course, at this stage, we don’t know if this means that dogs can “see” smells, even though the brain is capable of some pretty weird things.
“These results indicate that the olfactory system plays an important, if not dominant, role in canine cognition and has connections to most major information processing pathways, making it a vital network to consider when studying dog cognition,” the team concludes in their paper. .
Next, Andrews and his colleagues intend to map the olfactory systems of cats and horses. Both of them also have amazing senses of smell, but horses are herbivores, so they probably use their sense of smell in a very different way.
Preliminary evidence even hints that the olfactory tracts of the brain in cats may be even more extensive than in dogs.
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