Abstract
In natural environments, odors are typically mixtures of several different chemical compounds. However, the implications of mixtures for odor processing have not been fully investigated. We have extended a standard olfactory receptor model to mixtures and found through its mathematical analysis that odorant-evoked activity patterns are more stable across concentrations and first-spike latencies of receptor neurons are shorter for mixtures than for pure odorants. Shorter first-spike latencies arise from the nonlinear dependence of binding rate on odorant concentration, commonly described by the Hill coefficient, while the more stable activity patterns result from the competition between different ligands for receptor sites. These results are consistent with observations from numerical simulations and physiological recordings in the olfactory system of insects. Our results suggest that mixtures allow faster and more reliable olfactory coding, which could be one of the reasons why animals often use mixtures in chemical signaling.
Highlights
Most studies on olfactory processing have been performed with pure odorants [1,2,3,4,5,6] or with mixtures of few odorant components [7,8,9,10,11,12]
Odorants are chemicals that bind to olfactory receptors, where they are transduced into electric signals
Most natural olfactory stimuli are mixtures of several odorants, odor transduction has mainly been studied for pure odorants, and current models of odor transduction are inconsistent for mixtures
Summary
Most studies on olfactory processing have been performed with pure odorants [1,2,3,4,5,6] or with mixtures of few odorant components [7,8,9,10,11,12]. It has frequently been advocated that odor identity is encoded combinatorially by the distributed response pattern across olfactory receptor types [1,19,20,21,22]. For single odorants, response patterns often change significantly when the concentration varies [2,23] which poses a challenge to concentration-invariant recognition of odor identity. Could the lack of concentration invariance for single odorants be ameliorated by more complex natural odors that are mixtures of many odorants?
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