Ever wondered why a drop of perfume can drive you wild while a good dousing just drives you crazy?

A new study by Harvard Medical School (HMS) researchers is shedding light on how the olfactory system, which regulates the sense of smell, processes information with only 1,000 types of receptors to distinguish countless smells.

The research, published in today's issue of Cell magazine, was conducted by Linda Buck, an associate professor of neurobiology at HMS, and postdoctoral fellow Bettina Malnic. Junzo Hirono and Takaaki Sato, colleagues in Japan, also worked on the study.

Buck, who has been studying the sense of smell for 10 years, has discovered that each scenting cell, or neuron, has only one type of receptor. Each receptor type is found on about 5,000 neurons in a human nose, she said.

The neurons of each type are scattered throughout the nose, but they send messages that converge on distinct spots in the olfactory bulb at the front of the brain, Buck said. "What is most remark-able is that the locations of convergence are identical in different animals."

From the olfactory bulb, information flows to the olfactory cortex and then to other parts of the brain where the information is processed, Buck said.

The research helps to explain why differing concentrations of odorants can produce entirely different sensations. For example, the chemical indole is perceived as floral when diluted but smells putrid in high concentrations, according to a press release on the study.

"We call the set of receptors that recognize its odor its code," Buck said. "If you change the concentration of the odor, you can also get a change in its code."

Buck plans to follow the pathway of sensory information further into the brain. "We've looked so far at the nose and the bulb," she said. "We want to go into the cortex."

The full text of the paper can be found at http://www.cell.com.