Here’s what you’ll learn when you read this story:

• A new study analyzed 5.5 million neurons in more than 300 mice and determined that the arrangement of scent receptors isn’t as random as previously believed.
• By creating a “smell map” of a mouse’s olfactory system, scientists are now trying to discern why receptors are arranged in this specific pattern.
• Understanding how receptors arrange themselves could improve therapies for patients who have a diminished or entirely lost sense of smell.

The functions of human senses—sight, smell, taste, touch, and hearing—are remarkably complex and (for many senses) well-ordered. In the auditory cortex, for example, cells are arranged so that adjacent cells detect similar frequencies. Wander over to your visual cortex and you’ll find that neighboring neurons detect similar points in your visual field. However, when it comes to your nose, things are a bit more chaotic—or, at least, that’s what we once believed.

In a pair of studies published in the journal Cell, a team of scientists in the U.S. and Canada (led by experts at Harvard Medical School) discovered a hidden, orderly structure to olfactory senses by creating the world’s first “smell map.” To create this map, scientists relied on single-cell sequencing to identify which smell receptors were expressed in neurons, and then used spatial transcriptomics to figure out where those receptors were located.

Using this technique across 5.5 million neurons in more than 300 mice, they found that neurons were arranged in horizontal stripes from the top of the nose to the bottom, based on what receptor they expressed. This a big departure from previous research, which identified that receptors were organized in zones, but claimed that they were mostly dispersed at random within those zones.

“The organization of information in space is a major organizing principle for all sensory systems, and that is what has, until now, made olfaction super weird,” Sandeep Robert Datta, a researcher from from Harvard University and co-author of one of the papers, told The New York Times. “We have, to some extent, unveiled this long lost map for smell.”

These receptors—which are actually unique proteins—rest on neurons and bind to specific smells. While humans have hundreds of different types of receptors, other species have many more. Mice, for example, are believed to have at least 1,000 of them.

According to The New York Times, the researchers discovered additional genes that guided neuron development within the nose and now believe it’s possible that these genes will alter neuron expression based on their position within the nose itself. They found that this nasal receptor map also mirrored a similar arrangement in the olfactory bulb, which processes odor information before transmitting to the brain. This mirrored arrangement can also be seen in how topographic maps in the brain (in relation to the other senses) mirror their receptors.

“This is now arguably the most sequenced neural tissue ever, but we needed that scale of data in order to understand the system,” Datta said in a press statement. “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.”

While scientists have found this hidden structure in the nose, many more questions remain, including why certain receptors are located in their respective positions. It could be possible that, like our hearing and eye sight, similar neurons detect similar chemical structures. Or neurons could be organized by pleasing smells versus harmful smells. But the big payoff of this study is that a deeper understanding of how smell works could help scientists treat conditions where a person’s sense of smell is damaged or disappears entirely.

“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,” Datta said in a press statement. “Without understanding this map, we’re doomed to fail in developing new treatments.”