According to a new study published online in the Springer's journal Chemosensory Perception, anxiety can lead to an increased sense of smell which, in turn, can lead an individual to perceive a threat earlier. The study was led by Elizabeth Krusemark and Wen Li from the University of Wisconsin-Madison in the US, and has been published in a special issue of the journal, pertaining to neuroimaging of the chemical senses.
For their study, the researchers chose 14 healthy individuals with a normal sense of smell. They selected four neutral smelling substances ((acetophenone, guaiacol, anisole, eugenol) and two substances with offensive or negative odors (trimethylamine and valeric acid) and mixed them randomly to form three distinctive odors- neutral pure odor, neutral odor mixture, and negative odor mixture. The participants were exposed to these three odors and were asked to detect the presence or absence of a particular odor while undergoing a MRI scan. The breathing patterns of the participants were also monitored while they were detecting the various odors, as was the ability of their skin to conduct electricity (skin conductance response). The latter was done in order to measure the arousal level of the participants. The participants were also asked to self-rate their levels of anxiety.
The researchers observed that the ability to detect negative odors was in direct proportion to the level of anxiety of the participants. As the anxiety increased, so did the ability to detect negative smells. It was also noted that the skin conductance response increased when the participant felt threatened by a negative odor. The MRI scans revealed that in anxious individuals, there was an increased level of communication between the areas of the brain dealing with olfactory senses and emotions, when the participants were subjected to negative odors.
It was seen that the primary olfactory cortex detects even small, imperceptible olfactory threats in anxious state, and enhances its functional coupling with the circuits in brain dealing with emotions. According to the researchers, this heightened sensory-emotional coupling may be the reason behind the arousal of alertness to potentially threatening conditions.