Imagine a mouse rapidly and intermittently sniffing the crumbs it finds while foraging. Now compare it to a human bending down and taking one deep breath to determine if a cantaloupe is ripe.
A new study from Northwestern University has found that just like humans, mice can intentionally explore their environment with just one sniff. This is something scientists didn’t know before.
Two new complementary studies from Northwestern University will be published together on July 3. scientific progressstudied olfaction from opposite sides and found that rodents and humans rely on the same basic neurophysiology to process odors: motor and rhythmic components of the brain. The research shows that although mice have a much shorter sniff time than humans, the basic tempo of olfactory processing is the same. This result suggests that these sensory systems are fundamentally similar and have been conserved throughout evolution.
Taken together, the findings from the two labs have important implications. That means all mammals rely on a similar basic olfactory system, with unique twists on the same basic design. This research answers a fundamental question: how mice and humans sample their environments to understand them and predict what we want to do next.
“The real similarity lies in this single sniff, but it’s not just a sniff,” said corresponding author John M. Barrett, assistant professor of neuroscience at Northwestern University Feinberg School of Medicine. “The rat moves its hand while sniffing, which shows that it’s voluntary and that it’s doing it intentionally.”
What effect does it have on humans?
Changes in sniffing behavior are associated with diseases such as autism, Alzheimer’s disease and Parkinson’s disease, so understanding the basic wiring of the olfactory system could help with early detection and better treatment, the study authors said.
Knowing that we have this evolutionarily conserved set of mechanisms may help us understand how the mammalian brain works and, ultimately, how mammals fail in pathology. It helps you know how the brain works and how to fix it when it doesn’t work. ”
Andrew Sherif, first author
A tale of two papers
One study found that mice inspect food by smelling a single odor that is very similar to humans. Another discoverer was that humans organize odor information at high speed after just one sniff, and the form of olfactory brain processing is strikingly similar to that of rodents. Taken together, these separate but complementary studies suggest that there are common basic biological rules behind the olfactory mechanisms of these two mammals that have been conserved through evolution.
First study: Rats can smell like humans
The first paper started with a simple observation. When a mouse handles food, it will occasionally bring it a little closer to its nose before continuing to eat.
The study was conducted in the laboratory of Gordon MG Shepard in the Department of Neuroscience at Northwestern University Feinberg School of Medicine, along with colleagues locally and at the University of Pennsylvania and the University of Florida College of Medicine.
The researchers built a robotic multi-camera recording system to track mice as they forage and eat. Scientists led by Man Gao and Barrett in Sheppard Lab tracked the mouse’s hand and head movements in high resolution, while also tracking the mouse’s breathing.
The mice timed each sniff to the exact moment the food arrived in their noses, precisely coordinating their hands, heads, and breathing. Unlike regular sniffing when searching for food, this behavior is much like humans lifting food to their noses and carefully sniffing it before taking a bite.
The study found that mice sniffed more intensely when handling unappetizing food, but it wasn’t just the presence of the odor that triggered the behavior. When the scientists disrupted the mice’s sense of smell, the mice continued to sniff food as normal. What ultimately stopped this behavior was silencing the motor cortex, the area of the brain associated with conscious, purposeful movement.
“This means that when mice smell food, they are doing so as an active act of deliberate sensory sampling, rather than as a reflexive response to the odor,” said Gao, a postdoctoral researcher in Shepard’s lab. “Rather than passively sniffing, we found that mice chose to perform a quick ‘smell check’ that is characteristic of many human olfactory behaviors.”
This is the first study to document this deliberate, non-reflexive sniffing behavior in rodents in a real-world environment.
Second study: humans can process smells just like mice
The second study, conducted by Christina Zelano’s lab in Feinberg’s Department of Neurology in collaboration with Dr. Bruce Tan of Feinberg’s Department of Otolaryngology, sought to understand how humans can achieve the same perceptual accuracy as rodents with a single, slow sniff.
“We wanted to understand how humans can identify odors as quickly as rodents, even though our sense of smell is more than 10 times slower,” said Sherif, a postdoctoral researcher in Zelano’s lab. “By recording directly from the human olfactory bulb using a new technique, we were able to find rhythms of odor processing that closely resemble those in rodents, suggesting that the olfactory time window is conserved across species.”
The research team used a minimally invasive and highly accurate method developed in the Zelano lab to record the sense of smell in the brains of healthy human volunteers. Once intentionally inhaled by a participant, it induced low-frequency brain waves called theta oscillations (2-8Hz) in the human olfactory bulb, the exact same frequency that rodents smell. The study found that this slower brain rhythm helps organize the faster bursts of activity that occur when the brain is actually processing the smell. This means that the human brain can generate theta rhythm from a single odor and use it in the same way that rodents use sniffing cycles.
“The implications of our findings are important,” said co-author Qiaohan Yang, a graduate student in Northwestern University’s Department of Interfaculty Neuroscience. “In rodents, olfaction and theta are so tightly fused that the two are almost indistinguishable. In humans, slow sniffing pulls them apart, revealing theta oscillations to be independently generated distinct rhythms that can be fully engaged with a single deliberate inhalation.”
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Reference magazines:
Sheriff, A. others. (2026). Theta oscillations are the organizational unit of odor processing in the olfactory bulb. scientific progress. DOI: 10.1126/sciadv.aee1002. https://www.science.org/doi/10.1126/sciadv.aee1002
