Information pattern, odor

Odor/Structure Correlation attempts to elucidate the mechanisms which mediate the information transfer from structural featxires of a molecule to a corresponding information pattern. The latter originates in olfactory neurons and is encoded in nerve impulses. It is projected for further analysis, discrimination and recognition to the higher olfactory centers of the CNS. This information transfer includes the transduction process which converts chemical to electrical signals. 

Most, perhaps all of the odor theories advanced so far made the assumption that the transcription of structureil information encoded in the stimulant molecule into an odor information pattern is an integral process One odorivector (AMOORE, 2) interacts with one receptor site and this interaction resvilts in transcription of all structural components simviltaneously into their corresponding informational modalities. However, observation tells us that olfactory information is inherently complex Ambergris for instance is described (OHLOFF, 3) by six distinctly different notes. This would imply that in an integral process of the periphersil molecular interaction one single neuron has to detect at least six different profiles with six different receptor sites and project the informational modalities intact to the higher centers. 

All specific monoosmatic components are combined in still higher centers to produce an "Odor Information Pattern". 

Each discernible odor has a specific unique individusil odor information pattern. 

The next question arising is that about the minimum mmber of monoosmatic components required to encode an odor quality. It has been recognized by BEETS that an inherent "Principle of informational complexity" makes the perception of even a single odorant molecular species informationally complex, even if the odor information pattern is dominated by the terminal derivative (monoosmatic component) of a single chemoreceptory modality. But there has to be something like a minimum complexity still. In terms of the EMO there must be a minimum number of monoosmatic components essential to produce a minimal odor information pattern. Again, since this problem is not in the domain of peripheral processes, the Enzyme Model of Olfaction cannot provide an answer. However, experimental results obtained by POLAK (m) indicate that one... 

Two questions arise from this result. Do lobsters use only chemical and not mechanosensory information, and why do lobsters not use ground reference and head up-current Since turbulent odor dispersal is based on water flow patterns, we must investigate the role of microflow patterns in plume orientation behavior. As for ground reference, we speculate that the flow patterns of the lobster s natural environment may be too complex to allow for efficient rheotactic behavior in odor source localization. This complexity is most likely caused by a mismatch between turbulent scales and animal body size and sampling scales. 

Pioneering efforts to understand the nature of olfactory coding were reported by Adrian (24-27). His work introduced the ideas that different odors activate ORCs in different regions of the olfactory epithelium and that spatiotemporal patterns of ORC firing would suffice to encode different odors. Subsequent studies by many investigators and involving various recording methods (reviewed in refs. 13 and 28) led to the conclusion that, at various levels of the pathway, the olfactory system uses distributed neural activity to encode information about olfactory stimuli. 

Adults continue to associate new odors with pleasant and unpleasant situations in social and sex life, work and recreation, and concerning food and drink. The human patterns of odor recognition and preferences do not merely involve the olfactory nerve and its central projections. Learned associations are formed and stored in memoiy. To retrieve odor information, we need affective and cognitive components, as well as verbal descriptors. Without the latter, an odor appears familiar but cannot be labeled, the tip-of-the-nose-phenomenon (Lawless and Engen, 1977). 

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. 

All the information the fly needs for encoding quality, intensity and temporal variations of odors is present in the firing patterns of ORNs. We argue that, in Drosophila, all three features are encoded in the activity across a limited number of ORN classes (n 40) and is time dependent. Moreover, information about most odors is probably concentrated in a small subset of ORN classes. Because... 

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. 

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