Editors' ChoiceNeuroscience

Fragrance of Danger

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Science Translational Medicine  01 Jan 2014:
Vol. 6, Issue 217, pp. 217ec2
DOI: 10.1126/scitranslmed.3008237

We trust our senses because we think that they tell us the truth about our environment. The sound of explosions or the smell of fumes alerts us to potential danger, allowing us to actively avoid it. Much of the danger knowledge arises from learned experience and becomes stably integrated into our behavioral patterns. The memory of dangerous stimuli, including smells, was thought to be stored in the brain, where the sensory neuron information is received and interpreted.

New research by Kass et al. challenges this concept and suggests that sensory neurons themselves acquire a memory about dangerous smells and are on heightened alert to “sniff them out.” These data suggest that reward or punishment can directly influence how the sensory organs process information.

In an elegant set of experiments, Kass et al. trained a group of mice to associate a previously neutral odor with a mild foot shock. By using an approach that allows the visualization of neurotransmitter release from olfactory sensory neurons in vivo, the researchers revealed that fear learning can affect the strength of signals passing from these neurons to the brain. When mice traumatized by shock were reexposed to the fear-associated odor, their olfactory neurons responded with heightened sensitivity. The amount of neurotransmitter released by these neurons in response to the odor was significantly enhanced in comparison to the amount in control animals.

The knowledge that fear not only modifies the interpretation of sensory information but directly affects our senses contributes to a better understanding of the underlying mechanism. It might also influence the approach to treatment of anxiety and affective disorders, including posttraumatic stress disorder.

M. D. Kass et al., Fear learning enhances neural responses to threat-predictive sensory stimuli. Science 324, 1389–1392 (2013). [Abstract]

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