The shape of an odor fascinates Chris Chee, a graduate student in the Bower Lab.

"Odor is carried by wind and by water," she explains. "If you have, say, a cigarette, the smoke will form patches that are caused by turbulent eddies in the air as a plume is going up. What you will get is a discontinuous distribution of smoke."

Now she shifts her tiny frame on a chair perched in front of her computer in the office she shares with another student. "If your natural stimuli are invisible, discontinuous patches in a plume, how do you find the source of the odor?"

That's what Chee has been trying to explain for years, first as a Caltech graduate student studying the olfaction system in insects, then tracking the olfactory search patterns of rats.

Athletic and hip, Chee looks like she stepped out of an ad for the Gap. But she spent five years as an aerospace engineer before coming to Caltech, so her inclination is to build things --in this case, a theoretical framework for the mechanisms the nose uses to distinguish odors. How do we discern even the subtlest variations --from the difference between a rose and a gardenia to the distinctive aromatic chords of baked bread versus blueberry muffins?

The human olfactory pathway: Odor molecules enter the nose and stimulate the "chemosensitive" receptor neurons of the olfactory epithelium, which relays impulses to the olfactory bulb and tract.

Chee is also collaborating with two other Caltech labs attempting to devise an electronic nose. Nate Lewis's group has developed polymer sensors for chemical stimuli, while Rod Goodman's team is coming up with the hardware system to do olfactory pattern recognition. "There's one small part that remains: the biological side of it," Chris explains, which is where she comes in. "We always want to know how well an electronic nose compares to a biological nose, which is very sensitive to specific odors but is also capable of identifying a vast range of odors. Biology has the best of both worlds, and this poses a real challenge to engineering."

-- Linda Marsa