Two new studies, published this week, report that the roughly 400 types of smell receptors in the human nose are arranged in a precise spatial pattern rather than scattered at random — overturning a four-decade assumption that the olfactory epithelium was a random mosaic [1].

The first study, from a team at Duke and Harvard, used single-cell RNA sequencing of biopsied tissue from human noses to show that receptor types cluster in distinct zones from front to back and top to bottom of the nasal cavity [1]. The second, an anatomical mapping study, described the same gradient in donor tissue and named it the smell atlas [1].

The medical consequence is the part that travels. Smell loss is an early sign of Parkinson's, Alzheimer's, and the lingering form of long Covid, but clinicians have had no way to tell which receptor zones were impaired. A spatial map gives them one. Researchers told the Times that a clinical smell test calibrated to the atlas could become a low-cost early-warning tool, particularly for neurodegenerative disease [1].

The work has been a long time coming. Linda Buck and Richard Axel won the 2004 Nobel Prize for discovering the genes that encode the receptors. What they could not say, then, was where in the nose each gene was switched on. The atlas is the answer.

-- KENJI NAKAMURA, Tokyo