The head can be a competitive place. The eyes are known to battle with each other for dominance, as are the ears.
Now the nose has joined the fray. Wen Zhou and Denise Chen of Rice University report that when the nostrils are exposed separately to different odors, the nose doesn’t smell a blend but rather alternates between the two odors, as if the nostrils were fighting it out for supremacy.
This nostril rivalry, as the researchers describe it in a paperin Current Biology, is similar to what happens when the eyes are presented with different images, or the ears with different tones.
The researchers experimented with 12 people using two chemicals, one that has an odor like a marker pen, the other that smells like a rose. All 12 experienced switching between the two odors, with no pattern as to when and how often they switched.
The nose becomes habituated to odors quickly, and the researchers made use of this fact to examine the roles of the olfactory receptors and the cortex in the switching. In another experiment, they exposed one nostril to one of the chemicals for two minutes, long enough for the nostril to become habituated. When the same nostril was then re-exposed to the same chemical, the subjects found the smell much weaker. That, Dr. Chen said, suggests that the olfactory receptors in the nostril had adapted to the odor.
But when the other nostril was then exposed to the same chemical, the smell was weaker, too. “This shows there’s a central level of adaptation, too,” Dr. Chen said, in the brain.
Dr. Chen said that further exploration of the rivalry phenomenon should aid researchers in understanding the sense of smell. “Human olfactory perception is very much a field that’s in its infancy,” she said. “This opens a new area to study it.”