The smell of almonds is closer to that of roses than of bananas, the first-ever smell map reveals.
The map reveals the relative distance between various odors, according to Weizmann Institute scientists, and may help to unravel the basic laws underlying our sense of smell, as well as potentially enabling odors to be digitized and transferred via computer in the future.
The findings lend support to theory that, contrary to the commonly held view that smell is a subjective experience, there are universal laws governing the organization of smells, and these laws determine how our brains perceive them.
Two years ago, scientists revealed details of the tongue map, debunking the idea that there are just four taste locales on the licker.
To get a sense of what a smell map is, consider how most of us can tell that the musical note "do" is farther from "la" than from "re" on a scale — not only because our ears tell us the distance is greater, but because their frequencies are farther apart.
No such physical relationship had been discovered for smells, in part because odor molecules are much more difficult to pin down than sound frequencies.
To create their map, the scientists began with 250 odorants and generated, for each, a list of around 1,600 chemical characteristics. From this dataset, the Weizmann researchers, led by Rafi Haddad and David Harel, created a multidimensional map of smells that revealed the distance between one odor molecule and another.
Eventually, they pared the list of traits needed to situate an odor on the map down to around 40. They then checked to see whether the brain recognizes this map, similar to the way it recognizes musical scales.
They reexamined previous studies that measured the neural response patterns to smells in a variety of lab animals — from fruit flies to rats — and found that across all the species, the closer any two smells were on the map, the more similar the neural patterns. The results were detailed recently in the journal Nature Methods.
The scientists also tested 70 new odors by predicting the neural patterns they would arouse and running comparisons with the unpublished results of olfaction experiments done at the University of Tokyo. They found that their predictions closely matched the experimental results.
The research was supported by the Nella and Leon Benoziyo Center for Neurosciences, J&R Foundation, Eisenberg Keefer Fund for New Scientists, Arthur and Rochelle Belfer Institute of Mathematics and Computer Science, and the Henri Gutwirth Fund for Research.
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