The research from Northwestern University's Feinberg School of Medicine found that a single negative experience linked to an odor was enough to train the noise to detect danger, the university said Friday in a release.

The subjects in the study were exposed to a pair of grassy smells which were perceptually indistinguishable. They received an electrical shock when they were exposed to one scent, but not when they were exposed to the other one. After being shocked, the subjects learned to discriminate between the two similar smells.

"It's evolutionary," lead author Wen Li said in a statement. "This helps us have a very sensitive ability to detect something that is important to our survival from an ocean of environmental information. It warns us it's dangerous and we have to pay attention to it."

The findings are published in the journal Science.

--
Copyright 2008 by United Press International.
All rights reserved.
--