Temporal coding: Difference between revisions

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==A candidate for the neural code==

Simply put, a neural code can be defined as the minimum number of symbols necessary to express all biologically significant information.<ref> Theunissen F, Miller JP. ''Temporal Encoding in Nervous Systems: A Rigorous Definition''. Journal of Computational Neuroscience, 2, 149—162; 1995.</ref> ManyThere are many hypotheses about an encoding method; the main proponents of these include the idea of [[rate coding]] and temporal coding. However, many systems of the body utilize a more complex coding system than could be considered reasonable for a rate code. Recent research suggests that the more information Adense temporal code could solve this problem.

Neurons exhibit high-frequency fluctuations of firing-rates which could either be noise or carry information. Rate coding models suggest that these irregularities are noise, but this seems to be an inadequate explanation for a common occurrence. If the nervous system used only rate codes to convey information, evolution should have selecteddeveloped a more consistent, regular firing rate.<ref> J. Leo van Hemmen, TJ Sejnowski. 23 Problems in Systems Neuroscience. Oxford Univ. Press, 2006. p.143-158.</ref> The theory of temporal coding offers another solution to the problem of noise by suggesting that the apparent randomness of spikes is not completely randomarbitrary, but instead encodes information. This solution supplies an explanation for the “noise” and allows for a more information-rich code. To model this idea, binary symbols can be used to mark the spikes: 1 for a spike, 0 for no spike. Temporal coding allows athe sequence like 000111000111 to mean something different than 001100110011, even though the mean rate of firing is the same for both sequences, at 6 spikes/10 msec.<ref>Theunissen F, Miller JP. ''Temporal Encoding in Nervous Systems: A Rigorous Definition''. Journal of Computational Neuroscience, 2, 149—162; 1995.</ref>

Until recently, scientists had put the most emphasis on rate encoding, or using the mean frequency of spikes to convey information about the stimulus. However, functions of the brain are more temporally precise than mere rate encoding would seem to allow. In other words, essential information would be lost due to the inability of the rate code to capture all the available information of the spike train. In addition, responses are stochastic enough between similar (but not identical) stimuli to suggest that the different patterns of spikes contain a higher volume of information than is possible to include in a rate code. However, scientists are not confident about the implications of this additional dimensionality of the temporal code.<ref>{{cite web|last=Zador, Stevens|first=Charles, Anthony|title=The enigma of the brain|url=https://docs.google.com/a/stolaf.edu/viewer?a=v&pid=gmail&attid=0.1&thid=1369b5e1cdf273f9&mt=application/pdf&url=https://mail.google.com/mail/u/0/?ui%3D2%26ik%3D0a436eb2a7%26view%3Datt%26th%3D1369b5e1cdf273f9%26attid%3D0.1%26disp%3Dsafe%26realattid%3Df_h0ty13ea0%26zw&sig=AHIEtbQB4vngr9nDZaMTLUOcrk5DzePKqA|work=© Current Biology 1995, Vol 5 No 12|accessdate=4/08/12}}</ref>

==Evidence==