Temporal coding: Difference between revisions

Revision as of 12:50, 11 May 2012

Revision as of 10:24, 14 November 2012

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==Finding meaning in patterns==

Simply put, a neural code can be defined as the minimum number of symbols necessary to express all biologically significant information.<ref name="Theunissen F 1995">Theunissen F, Miller JP. ''Temporal Encoding in Nervous Systems: A Rigorous Definition''. Journal of Computational Neuroscience, 2, 149—162; 1995.</ref> There are many hypotheses about an encoding method, two of which are [[neural coding#Rate coding|rate coding]] and temporal coding. Many systems of the body utilize a more complex and information rich coding system than could be encoded in a rate code alone.<ref name="van Hemmen 2006">J. Leo van Hemmen, TJ Sejnowski. 23 Problems in Systems Neuroscience. Oxford Univ. Press, 2006. p.143-158.</ref> The two are often thought to work in conjunction, as in the gustatory system.<ref name="Carleton A 2010">Carleton, Alan, Riccardo Accolla, and Sidney A. Simon. (2010). [http://dx.doi.org/10.1016/j.tins.2010.04.002 "Coding in the mammalian gustatory system"]. ''Trends in Neurosciences'', 33(7):326–334.</ref> </b>

Neurons exhibit high-frequency fluctuations of firing-rates which could be noise or could carry information. Rate coding models suggest that these irregularities are noise, while temporal coding models suggest that they encode information. If the nervous system only used rate codes to convey information, a more consistent, regular firing rate would have been evolutionarily advantageous, and neurons would have utilized this code over other less robust options.<ref name="van Hemmen 2006"/> Temporal coding supplies an alternate explanation for the “noise," suggesting that it actually encodes information and affects neural processing. To model this idea, binary symbols can be used to mark the spikes: 1 for a spike, 0 for no spike. Temporal coding allows the sequence 000111000111 to mean something different than 001100110011, even though the mean firing rate is the same for both sequences, at 6 spikes/10 msec.<ref name="Theunissen F 1995"/>

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==Sensory systems==

===The gustatory system===

The mammalian [[gustatory system]] is useful for studying temporal coding because of its fairly distinct stimuli and the easily discernible responses of the organism.<ref>Hallock, Robert M. and Patricia M. Di Lorenzo. (2006). [http://dx.doi.org/10.1016/j.neubiorev.2006.07.005 "Temporal coding in the gustatory system"]. ''Neuroscience & Biobehavioral Reviews'', 30(8):1145–1160.</ref> Temporally encoded information may help an organism discriminate between different tastants of the same category (sweet, bitter, sour, salty, umami) that elicit very similar responses in terms of spike count. The temporal component of the pattern elicited by each tastant may be used to determine its identity (e.g., the difference between two bitter tastants, such as quinine and denatonium). In this way, both rate coding and temporal coding may be used in the gustatory system – rate for basic tastant type, temporal for more specific differentiation.<ref name="Carleton A 2010" />

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==References==

{{reflist}}

==Further Readingreading==

* Rullen, R. V. and Thorpe, S. J. (2001). Rate Coding Versus Temporal Order Coding: What the Retinal Ganglion Cells Tell the Visual Cortex. ''Neural Computation'', 13(6):1255—1283.

* Vanrullen, R., Guyonneau, R., and Thorpe, S. (2005). Spike times make sense. ''Trends in Neurosciences'', 28(1):1--4.