Neural coding: Difference between revisions

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'''Neural coding''' is a [[neuroscience]]-related field concerned with how [[sensory]] and other information is represented in the [[brain]] by [[neurons]]. The main goal of studying neural coding is to characterize the relationship between the [[stimulus]] and the individual or ensemble neuronal responses and the relationship among electrical activity of the neurons in the ensemble <ref name="Brown">Brown EN, Kass RE, and Mitra PP. 2004. Multiple neural spike train data analysis: state-of-the-art and future challenges. ''Nature Neuroscience'' 7:456-61</ref>.

== Overview ==

Neurons are remarkable among the [[cells(biology)]] of the body in their ability to propagate signals rapidly over large distances. They do this by generating characteristic electrical pulses called [[action potentials]] or, more simply, [[spikes]] that can travel down nerve fibers. Sensory neurons change their activities by firing sequences of action potentials in various temporal patterns, with the presence of external sensory stimuli, such as [[light]], [[sound]], [[taste]], [[smell]] and [[touch]]. It is known that information about the stimulus is encoded in this pattern of action potentials and transmitted into and around the brain. It is also discovered that [[muscles]] are activated by action potentials and that [[motor neurons]] serve to convert action potentials generated by the brain into muscle movements that allow animals to interact with the environment, often in response to sensory stimuli they receive from it.

Although action potentials can vary somewhat in [[duration]], [[amplitude]] and [[shape]], they are typically treated as identical stereotyped events in neural coding studies. If the brief duration of an action potential (about 1ms) is ignored, an action potential sequence, or spike train, can be characterized simply by a series of all-or-none point events in time <ref name="Gerstner">Gerstner, W. and Kistler, W. 2002. ''Spiking Neuron Models: Single Neurons, Populations, Plasticity''. Cambridge University Press, Cambridge</ref>. The lengths of interspike intervals (ISIs) between two successive spikes in a spike train often vary, apparently randomly, both within and across trials <ref name="Stein">Stein, R., Gossen, E. and Jones, K. 2005. Neuronal variability: noise or part of the signal? ''Nature Reviews Neuroscience'' 6:389–397</ref>. The study of neural coding, involves measuring and characterizing how stimulus attributes, such as light or sound intensity, or motor actions, such as the direction of an arm movement, are represented by neuron action potentials or spikes. In order to describe and analyze neuronal firing, [[statistical methods]] and methods of [[probability theory]] and [[stochastic point processes]] have been widely applied.

== Encoding and Decoding ==

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== Coding schemes ==

A sequence, or 'train', of spikes may contain information based on different coding schemes. In motor neurons, for example, the strength at which an innervated muscle is flexed depends solely on the 'firing rate', the average number of spikes per unit time (a '[[rate code]]'). At the other end, a complex '[[temporal code]]' is based on the precise timing of single spikes. They may be locked to an external stimulus such as in the [[auditory system]] or be generated intrinsically by the neural circuitry <ref name="Gerstner97">GERSTNER. 1997. Neural codes: Firing rates and beyond. ''Proceedings of the National Academy of Sciences of the United States of America'' 94:12740-12741</ref>.

Whether neurons use rate coding or temporal coding is a topic of intense debate within the neuroscience community, even though there is no clear definition of what these terms mean.