If you play sounds of many different frequencies at the same time, they combine to produce neutral “white noise.” Neuroscientists say they have created an analogous generic scent by blending odors. Such “olfactory white” might rarely, if ever, be found in nature, but it could prove useful in research, other scientists say.
Using just a few hundred types of biochemical receptors, each of which respond to just a few odorants, the human nose can distinguish thousands of different odors. Yet humans can’t easily identify the individual components of a mixture, even when they can identify the odors alone, says Noam Sobel, a neuroscientist at the Weizmann Institute of Science in Rehovot, Israel. Now, he and his colleagues suggest, various blends made up of a large number of odors all begin to smell the same—even when the blends share no common components.
Although many scents—such as coffee, wine, roses, and dirty socks—are complex blends containing hundreds of components, they are very distinctive. At least two factors are responsible, Sobel says: The individual odorants are often chemically related, and often one or more of them is vastly more intense than the rest.
The team’s findings are “a clever piece of work that shows the olfactory system works exactly as we would predict from our current understanding of it,” says Tim Jacob, a neuroscientist at Cardiff University in the United Kingdom. “That is, if you stimulate every olfactory ‘channel’ to the same extent, the brain cannot characterize or identify a particular smell,” he notes.
“Olfactory white is a neat idea, and it draws interesting parallels to white light and white noise,” says Jay Gottfried, an olfactory neuroscientist at Northwestern University’s Feinberg School of Medicine in Chicago, Illinois. The new study “definitely adds new information about how the brain interprets odors,” he notes.
Even though olfactory white is not likely to be encountered in nature, the concept could be useful, Gottfried says. “Researchers have found that white noise is a useful stimulus in experiments to probe auditory responses,” he notes, and scientists probing the human sense of smell might find similar uses for olfactory white.