Researchers from the University of Pennsylvania conducted a study in Philadelphia to explore how the sense of smell is registered by each nostril. The findings, published in Current Biology, show that the brain treats odors coming through the left and right nostrils with distinct timing and precision, revealing a surprising degree of independence in odor perception.
In total ten volunteers took part in the experiment. Researchers connected specialized tubes into both nostrils to deliver controlled scent stimuli. All participants had epilepsy, and electrodes had already been implanted in their brain structures as part of a therapeutic program known as vagus nerve stimulation. This therapy uses small electrical pulses to the vagus nerve to reduce seizure frequency and, in some cases, to stop seizures entirely.
The presence of implanted electrical stimulators made it possible to monitor brain activity continuously during the study. After placing the delivery tubes, the team introduced three different odors— eucalyptus, coffee, and banana—alternately to each nostril. Participants were asked to identify the scents while brain activity was recorded in the piriform cortex, the primary region of the cerebral cortex involved in odor discrimination.
The researchers observed that each side of the piriform cortex processed odor information from the nostrils in different time frames. When the same odor was presented alternately to both nostrils, the resulting brain signals were similar yet not identical, suggesting a degree of independent processing between the two pathways. Moreover, it emerged that information from the two nostrils could be transmitted to the brain more quickly and with greater accuracy than when both nostrils were used together.
As one physician involved in the study noted, the findings may have implications for understanding how people perceive complex scents in real-world environments and could inform future approaches to sensory disorders. The work adds to a growing body of evidence that lateralized processing in the olfactory system contributes to our nuanced sense of smell. The study builds on prior research into how unilateral olfactory input shapes perception and memory, and it aligns with theories about separate odor channels that feed into shared cortical networks (Attribution: Current Biology; University of Pennsylvania researchers).
In summary, the study demonstrates that the brain does not treat both nostrils as a perfectly unified channel. Instead, each nostril can drive slightly different temporal patterns of brain activity, which may influence odor identification accuracy and reaction time. The observation that two nostrils can inform the brain more rapidly than multiple nostrils at once adds another layer to our understanding of olfactory processing, with potential relevance for designing better diagnostic tools and therapies for sensory perception disorders (Attribution: Current Biology; University of Pennsylvania researchers).