Sniffing May Prepare Brain for Smelling.

The act of sniffing may be a wakeup call, alerting the brain to the imminent arrival of a smell, Stanford (Calif.) University researchers suggest. Therefore, processing of either sniff or smell signals--air rushing up the nose or odorant molecules latching onto nerve cells--could be defective in the many people who lose their ability to smell.

Every year in the U.S., more than 200,000 people visit their physicians complaining of problems with smell. Such a dysfunction affects most people with Parkinson's or Alzheimer's disease, often emerging as an early symptom of those conditions.

"We have discovered what appear to be two different aspects of olfactory processing," notes John Gabrieli, assistant professor of psychology. "One is the exploratory phase--the sniffing. And the second is the evaluative one--the smelling." Gabrieli, graduate student Noam Sobel, and their colleagues defined the sniff and smell phases as separate by looking at images of brain activity. When volunteers sniffed in the absence of any odor, brain images showed that an area called the piriform cortex was most active. When they actually detected a smell, other areas in the frontal lobe were most active.

The images showed some overlap between the brain...