BehindTheMedspeak: The smell of danger

Long story short: Your sense of smell is markedly improved after receiving a mild electric shock.

Who knew?

Charles Q. Choi, writing in the June, 2008 Scientific American:

Punishing Scents

Danger could make you smell new odors. In testing volunteers, scientists at Northwestern University used odor molecules that have the same chemical formula but are structured to be mirror opposites, like left and right hands. Such molecules ordinarily smell identical to people. But after getting zapped with mild electrical shocks when exposed to one molecule but not sniffing the other, volunteers rapidly learned to easily tell them apart. Functional MRI scans suggest that strong emotions could make the ancient smell centers of the brain quickly learn subtle differences between odors. The hypersensitivity seen in patients with some anxiety disorders could arise from a faulty ability to distinguish between true signals of danger and similar but less vital stimuli, the Northwestern team speculates, adding that its research could help develop new therapies. The electrifying findings appear in the March 28 Science.

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The abstract of that report follows.

Aversive Learning Enhances Perceptual and Cortical Discrimination of Indiscriminable Odor Cues

Learning to associate sensory cues with threats is critical for minimizing aversive experience. The ecological benefit of associative learning relies on accurate perception of predictive cues, but how aversive learning enhances perceptual acuity of sensory signals, particularly in humans, is unclear. We combined multivariate functional magnetic resonance imaging with olfactory psychophysics to show that initially indistinguishable odor enantiomers (mirror-image molecules) become discriminable after aversive conditioning, paralleling the spatial divergence of ensemble activity patterns in primary olfactory (piriform) cortex. Our findings indicate that aversive learning induces piriform plasticity with corresponding gains in odor enantiomer discrimination, underscoring the capacity of fear conditioning to update perceptual representation of predictive cues, over and above its well-recognized role in the acquisition of conditioned responses. That completely indiscriminable sensations can be transformed into discriminable percepts further accentuates the potency of associative learning to enhance sensory cue perception and support adaptive behavior.