Sensory coding

Dulac C. (2000). Sensory coding of pheromone signals in mammals. Curr Opin Neurobiol 10, 511-518. 

Response dynamics of B sensilla and the role of inhibition in sensory coding... 

Boeckh J. (1967) Inhibition and excitation of single insect olfactory receptors, and their role as a primary sensory code. In Olfaction and Taste, ed. T. Hayashi pp. 721-735. Pergamon, Oxford. 

Johanson, R.S. and Vallbo, A.B., Tactile sensory coding in the glabrous skin of the human hand, Trends Neurosci., 1983, 6, 27-31. 

The generated spike activity of the-different sensory cells in response to stimuli is decoded by the central nervous system (CNS). To investigate the sensory code of the receptor cells of a sensillum or several sensilla, different approaches can be used. The most direct method is to record from central neurons. In contrast to the investigation of central neurons responding to olfactory stimulations (Chapter 2), such recordings have been performed only recently from interneurons of the thoracic ganglion of the blowfly in response to the stimulation of tarsal contact chemoreceptive sensilla (Rook et al., 1980). 

Boeckh (1980) and Dethier and Crnjar (1982) have discussed currently proposed and identified sensory coding mechanisms. Three basic types of systems have been distinguished (i) labelled lines (ii) temporal patterns, and (iii) across fiber patterns. Possibly combinations of these coding systems may exist as well. 

Johansson, R. S. and VaUbo, A. B. (1983) Tactile Sensory Coding in the Glabrous Skin of the Human Hand, Trends in Neurosciences(TINS), 6, 1, 27 32. 

Taste receptor cells are organized into taste buds 825 Sensory afferents within three cranial nerves innervate the taste buds 826 Information coding of taste is not strictly according to a labeled line 826 Taste cells have multiple types of ion channels 826 Salts and acids are transduced by direct interaction with ion channels 826 Taste cells contain receptors, G proteins and second-messenger-effector enzymes 827... 

Olfaction, once thought to be a primitive sense, is now recognized as an elaborate sensory system that deploys a large family of odorant receptors to analyse the chemical environment. Interactions between these receptors and their diverse natural binding molecules (ligands) translate the world of odors into a neural code. Humans have about 350 odorant receptors. Rodents have more than a thousand. 

Digital Symbol Substitution Test. A subtest of the Wechsler Adult Intelligence Scale (WAIS), the Digital Symbol Substitution test measures sensory-motor integration and learning relationships of symbols. It has been used in many psychophar-macological studies. Subjects are given different forms of this test at each session. The test requires the patient to match as many of 100 symbols to their respective numerals, found in a code key, as possible within 60 seconds. 

Researchers have oscillated between emphasizing specificity of neurons ( labeled lines ) and responses to a spectrum of tastants by one cell. More recently, patterns of activation of a number of sensory cells are favored for coding specific taste sensations (Smith and Margolskee, 2001). Neural distinction of different tastes requires simultaneous activation of different cell types. The brain receives a single channel of information, simply bitter for a number of different compounds. 

As another example of sensory expansion, consider the genes that code the Kvl. 3 protein in mice. Researcher Debra Fadool of Florida State University gives mice a super-sense of smell by inactivating the gene for this protein. In other words, the mouse sensorium is held back from its reality perception, until we knock out the reality-restriction gene, and... 

All of these requirements point to an automated, wireless-readable sensory-based identification method and network that offers more functionalities and is significantly smarter than the well-known bar code or the unified product code (UPC). 

Sensory Analysis. A paired comparison test was run to determine if the difference in oil droplet size in the emulsion changed the perceived intensity of the orange flavor. The coarsest emulsion (3.87 pM) and the Microfluidized sample (0.90 pM) from the third set of spray dried samples were compared. The solutions were prepared using 200 ppm flavor in a 10% (w/v) sucrose solution with 0.30% of a 50% citric acid solution added. The amount of each powder required to attain 200 ppm orange oil was calculated on the basis of percent oil in each powder (determined by Clevenger analysis). A pair of samples at approximately 10 C was given to each of 24 untrained panelists. The samples were coded with random numbers. Half the panelists were asked to taste the coarsest sample first while while the other half tasted the Microfluidized sample first. This was done to determine whether or not adaptation was a factor. The panelists were asked to indicate which sample had the most intense orange flavor. 

Coding of olfactory information is a two-step process. First, sensory transduction converts chemical information in the environment into a code of action potentials. 

Second, the neural processing of this code defines a percept, called an odor . The first process takes place in a heterogeneous population of olfactory receptor neurons (ORNs) distributed in the epithelium. It determines which volatiles can be detected. The second process occurs in a series of neuropiles in the brain. It leads to some form of perception and can drive a behavioral response, depending on the animal s internal state and integration with other sensory modalities. How do individual neurons handle the transfer of information How do they connect to form a network in which this information is distributed, and what are the coding properties of this network ... 

We should not assume that odor coding at the level of the sensory neurons is a static phenomenon. Research on Drosophila gives us three cases where influences from the external or internal environment change response properties of ORNs. First, sensory adaptation can temporarily reset sensitivity of ORNs to persisting odorants. Next, circadian rhythms can cause daily cycles of ORN sensitivity. Finally, sensory neurons may change their synaptic properties as a result of chronic odor exposure. 

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