Olfaction stimuli

Generalizations. Several generalizations can be made regarding taste (16,26). A substance must be in water solution, eg, the Hquid bathing the tongue (sahva), to have taste. Water solubiUty is the first requirement of the taste stimulus (12). The typical stimuli are concentrated aqueous solution in contrast with the Hpid-soluble substances which act as stimuli for olfaction (22). Many taste substances are hydrophilic, nonvolatile molecules (15). Taste detection thresholds for lipophilic molecules tend to be lower than those of their hydrophilic counterparts (16). 

Meredith M. (1982). Stimulus access and other processes involved in nasal chemosensory function potential substrates for neuronal and hormonal influence. In Olfaction and Endocrine Regulation (Breipohl W., ed.). IRL Press, London, pp. 223-248. 

An animal s needs for stimulus diversity are difficult both to define and quantify (Carlstead 1996). Enrichment is often anthropomorphically rather than ecologically relevant (Chamove 1989), and due to human sensory biases we may fail to realize the importance of olfaction to less charismatic species, or those species with lower perceived levels of olfactory awareness (Hancox 1990 Somerville and Broom 1998). 

Different odor substances stimulate different patterns of ORCs in the olfactory epithelium, owing to the different sensitivity spectra of the ORCs (28). The pattern of activity in the epithelium evoked by a particular odor substance constitutes the first molecular image of that stimulus, which represents the determinants of the stimulating molecules (13). Thus, although olfaction is not a spatial sensory modality, in contrast, for example, to vision and somatosensation, the initial representation of an odor stimulus in the olfactory pathway does have spatial structure. 

The sensitivity and selectivity of olfaction and contact chemosensation are due (1) in the brain, to the existence of a neuronal network of neurons tuned to a specific chemical stimulus, and (2) in the periphery, to the existence of olfactory/ chemosensory receptor neurons housed in sensory microorgans called sensilla. The sensilla can best be viewed as simple cuticular porous extrusions that increase the surface that captures airborne odorants or chemicals dissolved in water droplets. They contain the receptive olfactory or chemosensory structures (Schneider, 1969). The olfactory sensilla are most numerous on the antennae and mediate the reception of sex pheromones and plant volatiles, as well as other odorants. Low volatility pheromones may also be detected by contact chemoreceptors on... 

In contrast to visual perception, where the sole stimulus is a photon, and even in contrast to olfaction with its structurally much more diversified stimuli, taste perception is exceptional, because the taste stimuli differ even more than odorants in size and chemical complexity, ranging from H+ ions to carbohydrates, amino adds, and proteins. Consequently, taste transduction mi t involve different mechanisms for different stimuli. In the ihesus monkey, taste reception has been located anatomically to defined loci at either the anterior or the posterior part of the tongue. 

Olfaction Discriminates Different Molecules and Different Stimulus Intensities... 

The ability to discriminate different molecules constitutes a criterion for olfaction. Because, as mentioned, anosmic persons can tell some pairs of odors apart based on nonolfactory cues, an experimenter must choose with care the compounds for study. 3-Phenethyl alcohol has an odor that many people find reminiscent of roses, and vapors from dilute solutions are widely accepted as an olfactory stimulus that does not interact with other chemosensory modalities in humans (Betcher Doty, 1998). Consider a human subject who can detect J3-phenethyl alcohol with the same sensitivity as nor-mosraics and can also detect -butanol (another alcohol often used for testing olfactory sensitivity (Hummel et al., 1997), which has an odor very different from that of P-phenethyl alcohol) with normal acuity. Suppose this subject cannot distinguish the two odors. How can an experimenter assess whether the subject exhibits the sense called olfaction ... 

If I can ascertain what another organism detects via olfaction, then I can perform experiments upon it, which cannot be performed on human subjects. The objective of such experiments—to find out how odor is coded—has yet to be achieved. Suppose the olfactory code were unraveled. Reproducing an odor would become a matter of replicating the pattern of neural responses without having to duplicate the chemical stimulus (much as cinematography appears to reproduce color without necessarily matching the complete spectroscopic profile of the original scene) (Robertson, 1992). 

If human olfaction can discern the filamentous character of scent plumes in air, then a headspace analysis, no matter how complete, might not suffice to reconstruct the fragrance. The distribution of molecules would play a role, as would the rate with which they are replenished after they have been depleted by sniffing. If, on the other hand, olfaction (independent of other sensory inputs) cannot differentiate a heterogeneous stimulus from one that has been well mixed with air, then a complete chemical analysis could serve to archive odors. 

Let me relate a piece of anecdotal evidence that suggests the dependence of olfaction upon the way that odors arrive at the nose. One of my students had been a subject in numerous signal detection experiments using weak solutions of P-phenethyl alcohol in water as a stimulus, in which she was inhaling its vapors in a continuous... 

In this paper we have proposed a simplified model of the insect AL in order to explore the neural code in olfaction. A possible role of the AL is to transform a multidimensional input vector representing the odorant stimulus into a spatio-temporal code given by a sequence of quasi-synchronized assemblies of PNs, in which each PN is individually phase-locked to the LFP. 

In olfaction, a transition from sea to land means that molecules need to be detected in gas phase instead of water solution. The odor stimulus also changes from mainly hydrophilic molecules in aqueous solution to mainly hydrophobic in the gaseous phase (discussed in Stensmyr et al. 2005). The olfactory system is also, like the rest of the organism, very prone to desiccation and mechanical abrasion in the terrestrial environment. All these new selection pressures take part in reshaping the sense of smell. Behavioral studies have provided evidence that some land-living crustaceans are very effective in detecting food from a distance and in responding to airborne odors, in short, that they have evolved an excellent sense of distance... 

Stearic acid was successfully delivered to the human oral cavity by emulsions at 67-69 °C where this stimulus is in liquid form [4, 22]. Detection thresholds were identified by orthonasal olfaction, retronasal olfaction, gustation, and a multimodal presentation where the lipid emulsion was placed in the oral cavity in the absence of nose clips [4]. Although measured at different temperatures, intensity responses for stearic acid were similar to the 18-carbon cis- unsaturated fatty acids linoleic and oleic acid. Oral detection thresholds for stearic acid in the human oral cavity with emulsions, yielded thresholds near 0.032% (w/v) [4, 22]. In addition, most study participants were able to detect stearic acid in the oral cavity [4,22]. 

The discriminatory capacity of the mammalian olfactory system is such that thousands of volatile chemicals are perceived as having distinct odors. It is accepted that the sensation of odor is triggered by highly complex mixtures of volatile molecules, mostly hydrophobic, and usually occurring in trace-level concentrations (ppm or ppb). These volatiles interact with odorant receptors of the olfactive epithelium located in the nasal cavity. Once the receptor is activated, a cascade of events is triggered to transform the chemical-structural information contained in the odorous stimulus into a membrane potential [58,59], which is projected to the olfactory bulb and then transported to higher regions of the brain [60] where the translation occurs. 

Olfaction is the sensory component resulting from the interaction of volatile food components with olfactory receptors in the nasal cavity. We generally speak of the aroma or odor of a food. The stimulus for this sensation can be orthonasaL (the odor... 

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