Stochastic pulse stimulation in chemoreceptors and its properties

Orientation towards food and mate, especially in insects, is an olfactory-controlled behavior which relies on the detection of small amounts of odorant molecules delivered in turbulent atmospheric conditions, so that randomness in magnitude and time is a major feature of the natural stimulus. The effect of random delivery on the initial step of olfactory transduction, the formation of the receptor-ligand complex, is analyzed in the case of the moth pheromonal system. Two types of randomness are compared, Gaussian (regular) and exponential (irregular). The influence of noise is quantified either with the maxima of the receptor-ligand complex, or with the times at which the concentration of complex crosses a given threshold level. It is shown that the stochastic features of the stimulus helps its detection and that the exponential distribution appears not only as a better description of the natural stimulus, but also as the most efficient from a biological point of view.