Israeli scientists listed the chemical characteristics of odorants, such as the smell of a rose, to draw up a unique map of scent.Scientists are one step closer to understanding the complexity of smell, after a new report by Israeli researchers has shown that smells can be mapped, and the relative distance between odors determined.
Smell is a complex and still little-understood sense. Odor molecules are far more difficult to pin down than sound frequencies. We know that the musical note, “do,” is farther from “la,” than “re,” on a scale because the frequencies are further apart and our ears can identify the difference. Until now, there was no similar physical relationship discovered for smells and it was impossible to know if the smell of almonds, for example, was closer to that of roses or bananas.
The researchers at Weizmann Institute of Technology collected together 250 odorants, and for each of these generated a list of about 1,600 chemical characteristics. From this dataset, the researchers, led by Rafi Haddad, a graduate student with Prof. Noam Sobel in the Neurobiology Department, and Prof. David Harel of the Computer Science and Applied Mathematics Department, together with their colleague Rehan Khan, created a multidimensional map of smells that revealed the distance between one odor molecule and another.
The researchers pared down 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, much as it would recognize musical scales.
They reexamined numerous previously published 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 scientists also tested 70 new odors by predicting the neural patterns they would arouse, and ran comparisons with the unpublished results of olfaction experiments done at the University of Tokyo in Japan. The Israeli researchers found that their predictions closely matched the experimental results.
These findings, which were published recently in Nature Methods, lend support to the scientists’ 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.
The research could help scientists unravel the basic laws governing our sense of smell, as well as potentially enabling odors to be digitized and transferred via computer in the future.
In September last year, Sobel and colleagues at the University of California announced that they had discovered a link between the molecular structure of a substance and whether it smells good or bad. This was the first time a known physical factor was discovered that could explain how our brains sense odors.