In animals, the sense of smell is an essential tool to detect, locate and identify predators in the surrounding environment. In fact, the olfactory-mediated defense system is so prominent in animals, that the mere presence of predator odours can evoke potent fear and anxiety responses.
Smells also evoke powerful emotional responses in humans.
Elizabeth Krusemark and Wen Li from the University of Wisconsin-Madison in the US hypothesized that in humans, detection of a particular bad smell may signal danger of a noxious airborne substance, or a decaying object that carries disease.
They exposed 14 young adult participants to three types of odors - neutral pure odour, neutral odour mixture, and negative odour mixture.
The researchers then asked them to detect the presence or absence of an odour in an MRI scanner.
During scanning, they also measured the skin's ability to conduct electricity - a measure of arousal level, and monitored the subjects' breathing patterns.
Once the odour detection task was over, and the subjects were still in the scanner, they were asked to rate their current level of anxiety. The authors then analysed the brain images obtained.
They found that as anxiety levels rose, so did the subjects' ability to discriminate negative odours accurately - suggesting a "remarkable" olfactory acuity to threat in anxious subjects.
The skin conductance results showed that anxiety also heightened emotional arousal to smell-induced threats.
The authors uncovered amplified communication between the sensory and emotional areas of the brain in response to negative odours, particularly in anxiety. This increased connectivity could be responsible for the heightened arousal to threats.
"This enhanced sensory-emotional coupling could serve as a critical mechanism to arouse adequate physiological alertness to potential insults," the researchers concluded.
The study has been published online in the journal Chemosensory Perception.
Source-ANI
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