Elizabeth Krusemark and Wen Li said smells evoke powerful emotional responses in humans and detection of a particular bad smell may signal danger of a noxious airborne substance, or a decaying object that carries disease.
The researchers exposed 14 young adult participants to three types of odors -- neutral pure odor, neutral odor mixture and negative odor mixture.
They asked the subjects to detect the presence or absence of an odor in an MRI scanner. During scanning, the researchers measured the skin's ability to conduct electricity (a measure of arousal level) and monitored the subjects' breathing patterns.
Once the odor detection task was over, with the subjects still in the scanner, they were asked to rate their current level of anxiety. The authors then analyzed the brain images obtained.
The study, published in the journal Chemosensory Perception, found as anxiety levels rose, so did the subjects' ability to discriminate negative odors accurately -- suggesting a "remarkable" olfactory (small) acuity to threat in anxious subjects.
Skin results showed anxiety heightened emotional arousal to smell-induced threats.