Nose divides sweet from foul

Even the inside of the nose can be a little cliquish. Like birds of a feather, nasal molecules that respond to pleasant smells flock together, keeping their distance from sensor molecules that pick up unpleasant smells.

Sensor molecules, or receptors, appear to be organized according to the pleasantness (or unpleasantness) of the odors they sense, a new study finds. For example, locations in the nose that respond strongly to one fragrant aroma will respond strongly to other delectable smells. Patches of nasal surfaces that process putrid stenches also handle specific sorts of smells and leave the rest of the work to someone else, Noam Sobel of the Weizmann Institute of Science in Rehovot, Israel and colleagues reported online September 25 in Nature Neuroscience.

The researchers inserted an electrode into 16 subjects’ noses and then showered the volunteers with six different scents. Because certain odors provoked stronger responses at different locations in the nose, the research team was able to confirm previous evidence suggesting a variegated nasal receptor surface.

“We’re not the first to find that,” says Sobel. But he and his colleagues have added an important new wrinkle. “Not only are the receptors organized in patches, but the axis that best describes their organization is pleasantness.”

This discovery sheds new light on a relatively poorly studied sensory organ. Compared with eyes or ears, scientists don’t know much about how the nose works.

“It’s interesting to see that the perceptual space would reflect itself on the peripheral level,” says Mats Olsson of the Human Olfaction Research Group at the Karolinska Institute in Stockholm, who was not involved in the study. Even more interesting, these results “may reflect an inherent pleasantness preference system” in the nose, he says.

An innate attraction to sugary smells and repulsion to acrid odors may  confer an evolutionary advantage by helping newborn babies seek out the food sources they need to survive.  This initial attraction is just a start, however.  The human olfactory system is extremely flexible, able to be remapped according to learning experiences.  Without this adaptive component, people might never have developed a taste for foul-smelling foods like limburger cheese, which don’t necessarily satisfy essential nutritional needs but sate certain cravings.

Soon people may be able to enjoy the tastes of such foods without the nasty smell, or just avoid repugnant aromas altogether. With a clear physical map of nasal receptors — a potential outcome of this research, says Sobel — scientists can target the regions that respond to unpleasant smells, even blocking odors from binding on the receptor level.  Products based on that approach would outperform perfumes, which simply mask the unpleasant aroma.