Many people consider the sense of smell less important than their other senses, despite its role in helping us interpret our environment, experience taste, and detect danger. For scientists, olfaction (the perception of airborne molecules) is still full of unanswered questions, especially when it comes to how smell receptors in the nose are organized.
To help lift the veil on this mysterious sense, researchers from Harvard Medical School have created the first detailed map of how more than a thousand smell receptors are arranged in the nose. The work marks a breakthrough in olfactory research and fills a long-standing gap in our understanding of the senses.
“Our results bring order to a system that was previously thought to lack order, which changes conceptually how we think this works,” said senior study author Sandeep Datta, professor of neurobiology in the Blavatnik Institute at Harvard, in a press statement.
The findings, published in Cell, could one day support the development of new and improved therapies for patients who have lost their sense of smell.
Olfaction Is Still Mysterious
Compared to other senses like vision, hearing, and touch, olfaction remains poorly understood at a biological level. Scientists already have detailed maps showing how receptors in the eyes, ears, and skin are organized, along with their corresponding brain areas.
“Olfaction has been the one exception; it’s the sense that has been missing a map for the longest time,” said Datta.
One reason for the delay is complexity. While vision relies on just three main types of receptors, olfaction depends on thousands.
Over the past 35 years, researchers have identified many of these receptors and attempted to map them, but they largely assumed the receptors, though confined to certain zones, were randomly arranged, without a consistent pattern. Interest in this question has grown in recent years, partly due to the sharp rise in smell loss following the COVID-19 pandemic, as well as advances in genetic techniques that allow scientists to study the system in much greater detail.
Read more: How to Improve Your Sense of Smell and Taste
Smell Receptors Are Surprisingly Highly Organized
In the new study, the research team used two genetic techniques, called single-cell sequencing and spatial transcriptomics, to analyze about 5.5 million neurons across more than 300 mice. This allowed them to pinpoint the exact location and connections of receptors and neurons.
“This is now arguably the most sequenced neural tissue ever, but we needed that scale of data in order to understand the system,” said Datta in the release.
The resulting map showed that smell receptors are arranged in tight, horizontal bands in the mice’s noses, grouped by type. Rather than being random, the system is highly structured.
“We show that development can achieve this feat of organizing a thousand different smell receptors into an incredibly precise map that’s consistent across animals,” Datta said.
The team also demonstrated that this receptor map aligns with existing maps of the brain’s smell-processing centers, offering new insight into how information travels from the nose to the brain.
Improving Therapies for Smell Loss
Next, the researchers aim to determine the exact order of these receptor bands. They are also expanding their work to human tissue to see how closely the mouse map translates across species.
A deeper understanding of how the sense of smell works could eventually support the development of targeted therapies, including stem cell treatments or even brain-computer interfaces. Losing the sense of smell can have surprisingly serious effects on mental health, leading to isolation, symptoms of anxiety, and depression.
“Smell has a really profound and pervasive effect on human health, so restoring it is not just for pleasure and safety but also for psychological well-being,” added Datta. “Without understanding this map, we’re doomed to fail in developing new treatments.”
This article is not offering medical advice and should be used for informational purposes only.
Read more: The 5 Senses Animals Have That Humans Don’t
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