Humans and other animals actively sense their surrounding environment. This entails the deliberate adjustment of motor behavior involved in sensory sampling (i.e., movements of the eyes, ears and hands) in line with the stimulus information.
When it comes to the sense of smell, the principal motor behavior that supports active sensing is the sniff, which entails brief inhalations aimed at pulling odor molecules into the nasal cavity. So far, the extent to which sniffing behaviors can be influenced and adapted based on the odors that one is smelling has remained unknown.
Researchers at Northwestern University recently carried out a study aimed at exploring this possibility. Their findings, published in Nature Human Behavior, suggest that people’s sniffing patterns are continuously shaped by what they are smelling and carry detailed information about specific odors.
“Our work was motivated by a long-standing interest in human breathing and sniffing,” Vivek Sagar, first author of the paper, told Medical Xpress. “We had previously observed that our human subjects smelled various odors in distinct ways. However, we were not sure to what extent information about each odor was present in the way odors were sniffed. Moreover, if this odor signature was reliably present in the sniffs, which brain areas were important for this effect?”
Mapping sniffing patterns for hundreds of odors
The primary objective of the recent study by Sagar and his colleagues was to reliably demonstrate that sniffing patterns are linked to odors. To achieve this, they analyzed a dataset that had been previously collected to examine neural underpinnings of odor perception and published in 2023.
The dataset they analyzed is called the neural encoding models of olfaction (NEMO) dataset. It contains the results of over 12,000 experimental trials during which three human participants were asked to smell 160 different odors inside a magnetic resonance imaging (MRI) scanner. MRI scanning relies on strong magnetic fields and radio waves to observe which body or brain tissues are most active at a given moment.
“We needed this rich dataset, since the effect size of odor-induced sniff modulation could be small,” explained Sagar. “We performed a repertoire of analyses to link sniffing dynamics to odor properties, but crucially, we could use a machine learning algorithm to predict which odor the subjects were sniffing based on their sniffing dynamics. Further, we could find the neural basis of this effect in the olfactory regions, such as the amygdala, by focusing our analysis on the MRI data.”
Probing the link between behavior and sensory perception
Interestingly, the researchers found that sniffing behaviors contained enough information to decode the identity of odors. Moreover, perceptual properties of odors appeared to be reflected in subtle sniffing pattern variations.
“We demonstrated that odor information can reliably influence sniffing dynamics, suggesting that olfaction is a closed-loop phenomenon with active sensing similar to other sensory systems, such as vision and audition, where stimulus characteristics influence the sampling behavior,” said Sagar. “Further, identifying brain regions such as the amygdala that are involved in this process is in line with previous work in epilepsy literature that has identified involvement of the amygdala in apnea and disruptions in breathing. “
This recent study by Sagar and his colleagues offers new valuable insight into how olfaction involves active sampling influenced by sensory stimuli similar to other modalities. It suggests that representations of odors are linked to sniffing behaviors, similarly to how visual stimuli are known to guide eye movements.
“A natural next step would be to further flesh out this link between sniffing and odor perception and test whether sniffing the same odor in different ways could alter odor perception in predictable ways,” added Sagar. “We are also interested in examining odor or breathing in different cognitive, affective, and spatial contexts.”
Written for you by our author Ingrid Fadelli, edited by Stephanie Baum, —this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive.
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More information
Vivek Sagar et al, The human brain modulates sniffs according to fine-grained perceptual features of odours. Nature Human Behaviour(2025). DOI: 10.1038/s41562-025-02327-x
Journal information:
Nature Human Behaviour
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