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The Journal of Neuroscience, July 25, 2007, 27(30):8071-8079; doi:10.1523/JNEUROSCI.1093-07.2007

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Behavioral/Systems/Cognitive
Benefits of Contrast Normalization Demonstrated in Neurons and Model Cells

Kate S. Gaudry and Pamela Reinagel

Division of Biology, Neurobiology Section, University of California, San Diego, La Jolla, California 92093-0357

Correspondence should be addressed to Pamela Reinagel, Division of Biology, Neurobiology Section, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357. Email: preinagel{at}ucsd.edu

The large dynamic range of natural stimuli poses a challenge for neural coding: how is a neuron to encode large differences at high contrast while remaining sensitive to small differences at low contrast? Many sensory neurons exhibit contrast normalization: gain depends on the range of stimuli presented, such that firing-rate modulation is not proportional to contrast. However, coding depends strongly on the precision of spike timing and the reliability of spike number, neither of which can be predicted from neural gain. The presumption that contrast normalization is associated with maintained coding efficiency remained untested. We report that, as contrast decreases, responses are more variable and encode less information, as expected. Nevertheless, these changes can be small, and information transmission is even better preserved across contrasts than rate modulation. The extent of contrast normalization is correlated with the extent to which information transmission is preserved across contrasts. Specifically, normalization is associated with maintaining the bits of information per spike rather than bits per second. Finally, we show that a nonadapting model can exhibit both contrast normalization and the associated information preservation.

Key words: adaptation; contrast gain control; information theory; coding; LGN; thalamus

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Received Nov. 11, 2005; revised May 1, 2007; accepted May 24, 2007.

Correspondence should be addressed to Pamela Reinagel, Division of Biology, Neurobiology Section, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357. Email: preinagel{at}ucsd.edu

This article has been cited by other articles:

				D. L. Beaudoin, M. B. Manookin, and J. B. Demb Distinct expressions of contrast gain control in parallel synaptic pathways converging on a retinal ganglion cell J. Physiol., November 15, 2008; 586(22): 5487 - 5502. [Abstract] [Full Text] [PDF]

				J. B. Demb Functional circuitry of visual adaptation in the retina J. Physiol., September 15, 2008; 586(18): 4377 - 4384. [Abstract] [Full Text] [PDF]

				M. Diaz-Quesada and M. Maravall Intrinsic Mechanisms for Adaptive Gain Rescaling in Barrel Cortex J. Neurosci., January 16, 2008; 28(3): 696 - 710. [Abstract] [Full Text] [PDF]

				K. S. Gaudry and P. Reinagel Contrast Adaptation in a Nonadapting LGN Model J Neurophysiol, September 1, 2007; 98(3): 1287 - 1296. [Abstract] [Full Text] [PDF]

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