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5 December 2013 11:26 am ,
Vol. 342 ,
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
- 5 December 2013 11:26 am , Vol. 342 , #6163
- About Us
It Just Smells
19 November 2012 3:25 pm
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.
For their study, the researchers used 86 nontoxic odorants that had a wide variety of chemical and physical properties such as molecular structure, molecular weight, and volatility. Those chemicals also spanned a perceptual scale from "pleasant" to "unpleasant" and another such scale on which scents were judged to range from "edible" to "poisonous." The researchers then diluted the chemicals so that their odors were equally intense. Finally, they created mixtures by dripping individual odorants onto separate regions of an absorptive pad in a jar, a technique that prevented the substances from reacting in liquid form to create new substances or odors. The odor blends contained anywhere from one to 43 of the chemicals, Sobel says.
In the tests, volunteers sniffed a mixture and then compared it with other mixtures made up of varying numbers of odorants. When the test mixture had just a few components, volunteers could easily distinguish it from the other blends, Sobel says. But as the number of odorants in a mixture rose above 20, volunteers began to perceive the blends as becoming more and more similar. By the time mixtures contained 30 or more components, most of the blends were judged to smell alike, the researchers report online today in the Proceedings of the National Academy of Sciences. The team dubbed the generic scent associated with large mixtures "olfactory white."
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.