Tag Archives: smell

Study finds new links between dogs’ smell and vision

Posted on August 8, 2022 | Leave a comment

Cornell researchers have provided the first documentation that dogs’ sense of smell is integrated with their vision and other unique parts of the brain, shedding new light on how dogs experience and navigate the world.

“We’ve never seen this connection between the nose and the occipital lobe, functionally the visual cortex in dogs, in any species,” said Pip Johnson, assistant professor in the Department of Clinical Sciences in the College of Veterinary Medicine and senior author of “Extensive Connections of the Canine Olfactory Pathway Revealed by Tractography and Dissection,” published July 11 in the Journal of Neuroscience.

“It makes a ton of sense in dogs,” she said. “When we walk into a room, we primarily use our vision to work out where the door is, who’s in the room, where the table is. Whereas in dogs, this study shows that olfaction is really integrated with vision in terms of how they learn about their environment and orient themselves in it.”

Erica Andrews, a former analyst in Johnson’s lab, is the paper’s first author and currently works in canine aging research.

Johnson and her team performed MRI scans on 23 healthy dogs and used diffusion tensor imaging, an advanced neuroimaging technique, to locate the dog brain’s white matter pathways, the information highways of the brain. They found connections between the olfactory bulb and the limbic system and piriform lobe, where the brain processes memory and emotion, which are similar to those in humans, as well as never-documented connections to the spinal cord and the occipital lobe that are not found in humans.

“It was really consistent,” Johnson said. “And size-wise, these tracts were really dramatic compared to what is described in the human olfactory system, more like what you’d see in our visual systems.”

Tractography, a 3D-modeling process, allowed Johnson and her team to map and virtually dissect the white matter tracts. The findings in the digital images were later confirmed by a co-author and white matter expert at Johns Hopkins University.

Johnson said the research corroborates her clinical experiences with blind dogs, who function remarkably well. “They can still play fetch and navigate their surroundings much better than humans with the same condition,” Johnson said. “Knowing there’s that information freeway going between those two areas could be hugely comforting to owners of dogs with incurable eye diseases.”

Identifying new connections in the brain also opens up new lines of questioning. “To see this variation in the brain allows us to see what’s possible in the mammalian brain and to wonder – maybe we have a vestigial connection between those two areas from when we were more ape-like and scent-oriented, or maybe other species have significant variations that we haven’t explored,” Johnson said.

Johnson plans to examine the olfactory system’s structure in the brains of cats and horses, which aligns with the broader goals of her research program – to leverage the most advanced imaging techniques, used commonly in human clinical research, to better understand animal brain physiology and disease.

Source: Cornell University Chronicle

Scientists uncover new details in how sense of smell develops

Posted on August 11, 2018 | Leave a comment

Dogs, known for their extraordinarily keen senses of smell, can be trained to use their sensitive sniffers to find drugs, bombs, bed bugs, missing hikers and even cancer. Among dogs and other animals that rely on smell, at least one factor that may give them an advantage is a sheet of tissue in the nasal cavity.

In humans, this tissue — called the olfactory epithelium — is a single flat sheet lining the roof of the nasal cavity. In dogs, however, the olfactory epithelium forms a complex maze, folding and curling over a number of bony protrusions, called turbinates, that form in the nasal cavity. The olfactory epithelium contains specialized neurons that bind to odor molecules and send signals to the brain that are interpreted as smell. Dogs have hundreds of millions more of these neurons than people do. It is assumed this added structural complexity is responsible for dogs’ superior ability to smell. But, surprisingly, that has never been shown scientifically.

Now, researchers at Washington University School of Medicine in St. Louis have uncovered new details in how the olfactory epithelium develops. The new knowledge could help scientists prove that turbinates and the resulting larger surface area of the olfactory epithelium are one definitive reason dogs smell so well.

The olfactory epithelium — a mouse’s is pictured in green — is a sheet of tissue that develops in the nasal cavity. Researchers at Washington University School of Medicine in St. Louis have uncovered new details on how the olfactory epithelium develops and why it is that some animals have such great senses of smell, compared with others that lack such ability.

“We think the surface area of the sheet matters in how well animals smell and in the types of smells they can detect,” said David M. Ornitz, MD, PhD, the Alumni Endowed Professor of Developmental Biology. “One reason we think this stems from differences in the complexity of these turbinates. Animals that we think of as having a great sense of smell have really complex turbinate systems.”

The study, published Aug. 9 in the journal Developmental Cell, also could help answer a longstanding evolutionary question: How did animals’ senses of smell become so enormously variable? The way these abilities came to diverge over evolutionary history remains a mystery. Understanding these signals could help scientists tease out how dogs evolved an extraordinary olfactory system and humans wound up with a comparatively stunted one.

First author Lu M. Yang, a graduate student in Ornitz’s lab, found that a newly discovered stem cell the researchers dubbed FEP cells control the size of the surface area of the olfactory epithelium. These stem cells also send a specific signaling molecule to the underlying turbinates, telling them to grow. The evidence suggests that this signaling crosstalk between the epithelium and the turbinates regulates the scale of the olfactory system that ends up developing, sometimes resulting in olfactory epithelia with larger surface areas, such as in dogs.

When the stem cells can’t signal properly, turbinate growth and olfactory epithelium surface area experience an arrested development. To study this in the lab, mice with such olfactory stunting could, in theory, be compared with typical mice to learn more about how these signals govern the final complexity of an animal’s olfactory system.

“Before our study, we didn’t know how the epithelium expands from a tiny patch of cells to a large sheet that develops in conjunction with complex turbinates,” Yang said. “We can use this to help understand why dogs, for example, have such a good sense of smell. They have extremely complex turbinate structures, and now we know some of the details about how those structures develop.”

Source: Washington School of Medicine in St Louis