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Monthly
288 pp. per issue, 6 x 9,
illustrated
Founded: 1989
ISSN 0899-7667
E-ISSN 1530-888X
2008 ISI Impact Factor: 2.378
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October 2007, Vol. 19, No. 10, Pages 2797-2839
Posted Online August 23, 2007.
(doi:10.1162/neco.2007.19.10.2797)
© 2007 Massachusetts Institute of Technology
Distortion of Neural Signals by Spike Coding David H. GoldbergDepartment of Physiology and Biophysics, Weill Medical College of Cornell University, New York, NY 10021, U.S.A. dhg2002@med.cornell.edu Andreas G. AndreouDepartment of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD 21218, U.S.A. andreou@jhu.edu
Analog neural signals must be converted into spike trains for transmission over electrically leaky axons. This spike encoding and subsequent decoding leads to distortion. We quantify this distortion by deriving approximate expressions for the mean square error between the inputs and outputs of a spiking link. We use integrate-and-fire and Poisson encoders to convert naturalistic stimuli into spike trains and spike count and inter-spike interval decoders to generate reconstructions of the stimulus. The distortion expressions enable us to compare these spike coding schemes over a large parameter space. We verify that the integrate-and-fire encoder is more effective than the Poisson encoder. The disparity between the two encoders diminishes as the stimulus coefficient of variation (CV) increases, at which point, the variability attributed to the stimulus overwhelms the variability attributed to Poisson statistics. When the stimulus CV is small, the interspike interval decoder is superior, as the distortion resulting from spike count decoding is dominated by a term that is attributed to the discrete nature of the spike count. In this regime, additive noise has a greater impact on the interspike interval decoder than the spike count decoder. When the stimulus CV is large, the average signal excursion is much larger than the quantization step size, and spike count decoding is superior.
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