Odor quality coding

Structure Recognition as a Peripheral Process in Odor Quality Coding... 

These results cannot be explained with any of the older theories of olfaction whereas the Enzyme Model of Olfaction not only can do that effortlessly, but actueLLly allows to predict these effects on the basis of generally accepted principles of molecular biochemistry. The concept of "STRUCTURE RECOGNITION AS PERIPHERAL PROCESS IN ODOR QUALITY CODING" represents only the special application of a more general mechanism of structvure recognition in peripheral processes to the problems of quality coding in olfac-r tion. 

Ma, Wei-Chun and Visser, J. H. (1978) Single unit analysis of odor quality coding by the olfactory antennal receptor system of the Colorado beetle. Ent. exp. appl., 24,520-33. 

Statistical evaluation of the degree to which the synthetic sample (prepared by adding the above three compounds to nonirradiated enzyme-inactivated beef) differed from enzyme-inactivated irradiated beef, was determined. Using the score sheet given in Figure 4, panel members evaluated the odor quality of a standard sample (S) and two coded samples (one of which was identical with the standard) and indicated the degree of difference noted. Two sets of samples were tested in a single session. One had irradiated beef slurry as the standard sample (Set I, Table VII). The... 

Therefore the firing rate of ORNs is not an exact reflection of the dynamics of odor pulses. More importantly, the temporal correlation of firing with odor concentration differs between ORN classes and between odors that stimulate the same class. This suggests a temporal dimension to the odor code at the level of the ORN population. Getz and Akers (1997) calculated that the information content of the phasic period of ORNs is much higher than the tonic period suggesting odor quality can be assessed relatively fast and is not dependent on the duration of odor pulses. In addition to the instantaneous pattern of activity across ORNs, the comparison of on-off dynamics between ORN classes may also contain information. 

If odor-evoked slow temporal patterns actually provide higher brain centers with information about the odor quality, identification and discrimination cannot be instantaneous as many of the temporal features in the response profiles appear late or even after offset of odor exposure. Honeybees need 500 ms for a response to (non-sexual pheromone) odors but at least 1 second of stimulation is required for a correct discrimination (J. Klein, unpublished, cited in Galizia el al., 2000a). Thus, it appears that time is an important factor in discrimination tasks involving non-pheromonal odors and the slow temporal patterns could theoretically contribute to an olfactory code. In contrast, these temporal patterns would be too slow to encode information about sexual pheromones. Male moths, for example, must be able to respond to rapid changes in stimulus intermittency when moving upwind in pheromone plumes in search of a calling female. 

If a spatial olfactory code underlies a subsequent identification of an odor, then we would expect concentration-dependent variations of odor maps to have an impact on the perceived odor quality. Stimulus concentration can indeed influence perception of odor quality and behavior of insects. For example, olfactory responses of the fruit fly, Drosophia melanogaster, shifted from attraction to repulsion as the concentration increased (Siddiqi, 1983 Stensmyr et al., 2003). Future studies should thus involve correlations of behavior with glomerular activity at different concentrations. 

In addition to the spatial representations of odorant structural features on the surface of the OB, several electrophysiological studies proposed the temporal coding of odor quality and intensity by neuronal populations in the fish OB (Kang and Caprio 1995 Friedrich and Laurent 2001). For details, see the reviews by Laberge and Hara (2001) and Friedrich (2002). 

Mackay-Sim, A., Shaman, P. and Moulton, D.G. (1982) Topographic coding of odor quality odorant-specific patterns of epithelial responsivity in the salamander, Ambystoma tigrinum. Anat. Embryo ., 170, 93-97. 

Up to now it was not possible to establish general rules as to correlations between odor quality and chemical structure. Some valuable concepts have, however, been established by approaching the molecular basis of stimulant interaction at the olfactory receptor level (16, 34, 35, 36, 45, 46, 313, 346, 446, 448, 452, 602, 630, 631). The attempts to create a code of odor impressions for flavors are still rudimentary (213, 447, 612). Psychologists interested in sensory measurements try to use physicochemical data of stimuli to establish empirical sensory correlations (131, 238, 324, 365, 392, 393, 396, 477, 533). Several techniques for the characterization and measurement of odor qualities for practical purposes have been described (328, 392, 477). 

Ventilation can reduce odors in a room and dilute cigarette smoke. Older air quality standards found in building codes have their origin in studies of acceptable levels of body odor and cigarette smoke. Ventilation can control microorganisms, dusts, and other particulates in hospitals and clean rooms. Some clean rooms use laminar flow to prevent the distribution of particulates in the room. 

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