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Shock and Awe: a View into Odor and Experience

Posted: April 1, 2008

A new report in the journal Science authored by Wen Li et al. focuses on the relationship between experience and odor perception in humans. "Adverse Learning Enhances Perceptual and Cortical Discrimination of Indiscriminable Odor Cues" details the responses of 12 subjects to two pairs of similar olfactive molecules: rose oxide and its chiral counterpart and two butanol molecules. At first, the subjects were unable to detect any difference between the two sets of molecules, measured via MRI. Following seven or fewer electric jolts administered to subjects during sniffing of one of the smells, subjects were in fact able to distinguish the molecules. In addition, subjects' reactions changed toward the shock-linked molecules. No change in perception was observed in relation to the molecules not linked to the electric jolts. While the results are very preliminary, there is some thought that the authors' work could lead to understanding and treatment for chemo-sensitive individuals.

The full abstract:

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.