Odour plumes

Murlis, J. and C. D. Jones. Fine-scale structure of odour plumes in relation to insect orientation to distant pheromone and other attractant sources. Physiol. Entomol. 6, 71-86 (1981). 

Vickers N. J., Christensen T. A., Baker T. C. and Hildebrand J. G. (2001) Odour-plume dynamics influence the brain s olfactory code. Nature 410, 466 470. 

Key words Pheromone detection, chemotaxis, computational neuroscience, moth, olfaction, odour plumes. 

Olfactory receptor neurons not only have to be selective to a spectrum of molecules, they must also report the quantity or concentration of molecules in the environment and also temporal properties. Receptor neurons respond to fluctuations in stimulus concentration with changes in action potential firing frequency. We also see very clear diversity in the temporal responses of ORNs responsible for pheromone detection in S. litoralis (J. Mackenzie et al, unpublished) which may suggest that the Ifont end of the pheromone detection system in the moth is tuned to different frequency information which is presumably rich in turbulent odour plumes (see Section 4). In solving the problem of chemieal source localisation the capture of temporal information has already been demonstrated to be important [15]. 

Figure 1. Tracking experiments performed with our olfactory robot We have equipped a koala robot with two gas sensor arrays and performed tracking experiments with the robot moving in an arena. The visualisation of the odour plume can he seen at the left and robot trajectories at the right. The ethanol source was placed at (x,y)=(240,100) and released at a low rate of 0.35 1/min. Over 16 runs performed with the robot starting from the same location (x,y)=(20,70), 13 have successfully converged to the source location [4].

Murlis, J. 1986. The structure of odour plumes. In Mechanisms in Insect Olfaction (Ed by T.L. Payne, C.E.J. Kennedy M.C. Birch), pp 27—38. Oxford Clarendon Press. 

Observations of smoke plumes, first brief tests and some papers 15, 6/ suggest that the immission concentration is fluctuating in a wide range near the source. Human nose is more sensitive to odour concentration fluctuation than, due to adaption, to constant odour concentration. In fig. 5 it is shown qualitativly that odour perception may occur due to concentration fluctuations although the mean value is far below the odour threshold. In table 1 it is indicated that the distance between agricultural emission sources and receptor is relatively small in relationship to industrial emissions. 

Therefore, what is relevant to the animal behaviourally and how it interacts with the environment determines its biological setup (Figure 2). The odour stimuli in which moths are primarily interested are plumes with fast temporal features and complex blends. This has implications for the form and function of the AL and its inputs. For instance, it has been suggested that there are ORNs specifically designed for detection of flux in pheromone components. 

Vickers NJ (2000) Mechanisms of animal navigation in odor plumes. Biol Bull 198 203-212 Voigt CC, von Helversen O (1999) Storage and display of odour by male Saccopteryx bilineata... 

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