The secret lab in cats’ noses: How felines became nature’s chemists

COLUMBUS, Ohio — Our feline friends enjoy a sense of smell that’s roughly 14 times stronger than that of a human. While we have about five million odor sensors in our noses, cats have over 200 million! Cats use their sense of smell as their primary means of identifying people and objects. However, until now, the exact mechanism behind their olfactory prowess remained a mystery. Exciting research from Ohio State University scientists has uncovered the secret behind cats’ extraordinary sense of smell.

Study authors say cats owe their strong sense of smell to a collection of tightly coiled bony airway structures. These findings, published in PLoS Computational Biology, were reached via the first ever detailed analysis of the domestic feline’s nasal airway.

The research team developed a new 3D computer model of the cat nose, and then used that to simulate how inhaling air containing common cat food odors would flow through the coiled structures. This led to the discovery that the air actually divides into two separate flow streams; one that is cleansed and humidified and another that delivers the odorant quickly and efficiently to the system responsible for smelling (the olfactory region).

In other words, the study suggests that a cat’s nose functions as a highly efficient and dual-purposed gas chromatograph, a sophisticated device typically found in chemistry labs for separating and analyzing complex mixtures. Researchers explain the feline nose is so efficient at this function, its structure and design could actually inspire improvements to the gas chromatographs used today in countless labs.

This discovery not only sheds light on why cats have such a keen sense of smell but also provides insights into the evolution of mammalian olfactory systems.

While the long nose of an alligator has also been found to mimic gas chromatography, researchers theorize that the compact head size of cats drove an evolutionary change resulting in a labyrinthine airway structure that helps felines adapt to diverse environments.

Prof. Zhao’s lab had previously developed models of both rodent and human noses in order to study air flow patterns, but this latest high-resolution cat model and subsequent series of simulation experiments are the most complicated to date. This was achieved via micro-CT scans of a cat’s head and microscopic-level identification of tissue types throughout the nasal cavity.

“We spent a lot of time developing the model and more sophisticated analysis to understand the functional benefit that this structure serves,” he notes. “The cat nose probably has a similar complexity level as the dog’s, and it’s more complex than a rodent’s – and it begs the question – why was the nose evolved to be so complex?”

Computer simulations of breathing revealed the answer. During a simulated inhalation, study authors noted two distinct regions of air flow; respiratory air that is filtered and spreads slowly above the roof of the mouth on its way to the lungs, as well as a separate stream containing odorant that moves rapidly through a central passage directly to the olfactory region closer to the back of the nasal cavity.

The analysis also accounted for both the location of flow and the speed of its movement through turbinates, or the bony structures inside the nose.

“We measured how much flow goes through specific ducts – one duct that delivers most odorant chemicals into the olfactory region, versus the rest, and analyzed the two patterns,” Prof. Zhao comments. “For respirant breathing, turbinates branch to divert flow into separate channels, sort of like a radiator grid in a car, which would be better for cleansing and humidifying.

“But you want odor detection to be very fast, so there is one branch that delivers odor at high speed, potentially allowing for quick detection rather than waiting for air to filter through the respiratory zone – you could lose most of the odor if air has been cleansed and the process is slowed down.”

In a gas chromatograph, a sample is vaporized and carried through a long, coiled tube. Different components of the sample travel at different speeds based on their chemical properties, allowing for their separation and identification.

The cat’s nose works on a similar principle. As air is inhaled, it passes through the coiled turbinates. Odor molecules in the air interact with the mucus-covered walls of these passages, with different molecules “sticking” to the walls at different rates. This process effectively separates the odor molecules, allowing the cat’s brain to process them more efficiently.

The simulation also revealed that the air sent to the olfactory region is eventually recirculated in parallel channels when it gets there. “That was actually a surprise,” Prof. Zhao says. “It’s like you take a sniff, the air is shooting back there and then is being processed for a much longer time.”

This setup provides cats with two significant advantages. First, it allows for rapid detection of odors, which is crucial for sensing potential prey or predators. Second, it enables more detailed analysis of complex odors, which could be useful for identifying subtle differences in scents left by other animals.

This project was the first ever to quantify the difference in gas chromatography between mammals and other species. Prof. Zhao and his team estimate a cat’s nose is over 100 times more efficient at odor detection than an amphibian-like straight nose in a similarly sized skull. This study was also the first to produce a parallel gas chromatography theory: parallel olfactory coils feeding from the high-speed stream to increase the effective length of the flow path while slowing down the local airflow speed, potentially to produce better odor processing.

“We know so much about vision and hearing, but not so much about the nose. This work could lead to more understanding of the evolutionary pathways behind different nose structures, and the functional purpose they serve,” Prof. Zhao concludes.