New research from Northwestern University announced on July 3 has found that mice, like humans, can take a single sniff to deliberately probe their environment—an ability previously unknown in rodents. Two complementary studies, set to be published together in Science Advances, examined the sense of smell from different perspectives and discovered that both species rely on similar neurophysiological mechanisms for olfactory processing.
The studies found that although a mouse's single sniff is much shorter than a human's, the underlying tempo of smell processing remains consistent between the two. The results suggest these sensory systems are fundamentally similar and have been preserved through evolution. "The true similarity is this single sniff, but it's not just a sniff," said John M. Barrett, research assistant professor of neuroscience at Northwestern University Feinberg School of Medicine. "Mice even move their hands while sniffing, which shows it's volitional—they're doing it on purpose."
One study observed that mice inspect food using deliberate single sniffs reminiscent of human behavior when evaluating food by smell. The other study showed that humans organize odor information rapidly within a single sniff—a process resembling rodent brain activity during olfaction. Together, these findings indicate there are shared biological rules behind how mammals process smells.
The first paper involved tracking high-resolution movements and breathing patterns in mice as they foraged for food using a robotic multi-camera system developed by Gordon M.G. Shepherd’s lab at Northwestern University Feinberg School of Medicine with collaborators from the University of Pennsylvania and University of Florida College of Medicine. The researchers found that silencing the motor cortex—responsible for intentional movement—stopped the food-sniffing behavior in mice, but interfering with their sense of smell did not affect it.
"This means when mice sniff food, they're not doing it as a reflexive response to an odor, but rather as a proactive act of deliberate sensory sampling," said Mang Gao, postdoctoral scholar in Shepherd’s lab.
In parallel work led by Christina Zelano’s team at Feinberg and Dr. Bruce Tan from otolaryngology at Feinberg, researchers used minimally invasive methods to record brain activity during intentional inhalation in healthy human volunteers. Sheriff, postdoctoral scholar in Zelano’s lab, said, "We wanted to understand how we can identify odors as fast as rodents do even though we sniff over 10 times slower." They discovered low-frequency theta oscillations (2–8 Hz) generated by single sniffs matched those seen in rodents’ brains during smelling tasks.
Qiaohan Yang, graduate student at Northwestern Interdepartmental Neuroscience program, concluded, "In rodents, sniffing and theta are so tightly fused that the two are nearly indistinguishable. In humans...the slower sniff rate pulls them apart...a single deliberate inhalation is sufficient to engage."
