Stimulus concentration, taste

Moskowitz, H. R. and Arabic, P. 1970. Taste intensity as a function of stimulus concentration and solvent viscosity. / Texture Stud. 1 502-510. 

One of the goals in gustatory neurobiology is to understand how information about taste stimuli is encoded in neural activity. The taste is defined by two parameters taste primary and intensity (stimulus concentration). Historically, there have been two major theories of neural coding in the taste system. These are the labeled line (Frank 1973) and across fibre (or neuron) (Erickson et al. 1965) pattern theories. Both of these theories are focused on the spatial representations of neuronal activity. 

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). 

The binding specificity of d-[ C]glucose by the taste-papillae membranes, compared to that of control membranes isolated from epithelial tissue, has been confirmed in two studies. One inherent problem in the approach is that the stimuli, primarily carbohydrate sweeteners, are not ideal model compounds to use, as they are not active at low concentrations and do not show sufficiently high binding-constants. The use of other stimulus compounds that are at least several hundred times sweeter than sucrose, such as saccharin, dihydrochalcone sweeteners, dipeptide sweeteners, stevioside, perillartine and other sweet oximes, the 2-substituted 5-nitroanilines, and... 

Chemoreceptor A sensory receptor responding to a chemical stimulus (e.g., smell or taste) or change in the concentration of a chemical (e.g., H+ ions in the blood or PH). 

Johnsen and Teeter (1982) demonstrated that bullheads could be conditioned to respond to chemical concentration differences presented across their maxillary barbels. These structures contain taste receptive fields innervated by the facial (VII) nerve. Fish responded to concentration differences as small as 10%, but the minimum discernible difference in concentration depended on the concentration of the stimulus. At higher concentrations, larger differences between the left and right barbels were required for the fish to show an appropriate behavioral response. 

A series of increasing concentrations of a chemically pure stimulus material in a neutral substrate (water or oil) may be used to determine sensory thresholds to those compounds. The assessors have to indicate the concentration at which stimulus is perceived for two successive concentrations. Increasing concentrations of sucrose, sodium chloride, citric acid, and caffeine are used for the basic tastes sweet, salt, acid, and bitter. Likewise, the olfactory threshold is determined by using some odorants in aqueous or alcoholic solutions (absolute ethanol is often used as a solvent), to measure the ability of the panelists to identify an odor impression and evaluate their odor memory. 

Threshold This is for the recognition of taste, odor, and flavor components. A series of solutions in order of physical concentration of the stimulus is used to determine the absolute threshold (ascending forced choice). 

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