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Fear Factor
It has generally been assumed that the most basic aspects of peripheral sensory processing do not change even if they are paired with reward or punishment. A smell should still smell the same, a color should still look the same, and any changes observed would be likely to occur downstream of the primary sensory processing areas. However, using longitudinal in vivo neurophysiology in transgenic mice, Kass et al. (p. 1389) observed that neurotransmitter release from olfactory sensory neurons themselves was selectively enhanced for threat-predictive odors after fear conditioning.
Abstract
The central nervous system rapidly learns that particular stimuli predict imminent danger. This learning is thought to involve associations between neutral and harmful stimuli in cortical and limbic brain regions, though associative neuroplasticity in sensory structures is increasingly appreciated. We observed the synaptic output of olfactory sensory neurons (OSNs) in individual mice before and after they learned that a particular odor indicated an impending foot shock. OSNs are the first cells in the olfactory system, physically contacting the odor molecules in the nose and projecting their axons to the brain’s olfactory bulb. OSN output evoked by the shock-predictive odor was selectively facilitated after fear conditioning. These results indicate that affective information about a stimulus can be encoded in its very earliest representation in the nervous system.
