Chee's initial experiments were with cockroaches -- studying the insect nervous system. "I would videotape the movements of cockroach antennas in response to food odors," she recalls. "I saw there were definite patterns of movement that were very different from when there were not odors present. So what kind of processing was going on in response to this stimulus?" That observation prompted her to theorize that antennal movement, in addition to the antenna's olfactory sensitivity, are somehow used together by the animal to sense which direction the odor comes from.

Wind tunnel wherein rats search for odors.

To explore the issue with vertebrates, Chee, with high school student Sharlene Wu, used a small wind tunnel (4'x 10'x 2') -- a controlled environment that would enable them to study how rats search for and locate an odor. They released an odor from one of three sites in the tunnel and videotaped the rat attempting to discover the source of the smell. By interrupting the flow of the odor at different phases of the rats' search, the scientists could see at what point the rats actually determined where the odor was coming from. And in talking to other scientists, they realized the search patterns they saw in rats are very similar to those in invertebrate animals -- "except for one phase," she says. "Rats show a distinctive behavior where they cross the wind tunnel perpendicular to the airflow, indicating that knowledge of wind direction (that is, non-olfactory information) is important to the rat during the search."

Rat's-eye view of the wind tunnel.

Given the commonalities in search behavior among all animals studied, it's possible these patterns could be used by humans as well. The wind tunnel tests strongly suggest that the act of locating odors is mediated not only the olfactory brain -- the area used to detect and identify an odor -- but also by an entirely different brain sensing system, the mechano-sensory, or tactile system. If so, olfactory search may be much more complex than merely detecting or even identifying odors, requiring the coordination of at least two different sensory systems and regions of the brain. (Just remember that the next time you walk down the street, smell the odor of warm apple pies, and sniffing around, turn to see a small bakery to your left with a rack of pies cooling by the window.)

-- Linda Marsa