Wessel, Ralf and Koch, Christof and Gabbiani, Fabrizio (1996) Coding of time-varying electric field amplitude modulations in a wave-type electric fish. Journal of Neurophysiology, 75 (6). pp. 2280-2293. ISSN 0022-3077. http://resolver.caltech.edu/CaltechAUTHORS:20130816-103238016
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1. The coding of time-varying electric fields in the weakly electric fish, Eigenmannia, was investigated in a quantitative manner. The activity of single P-type electroreceptor afferents was recorded while the amplitude of an externally applied sinusoidal electric field was stochastically modulated. The amplitude modulation waveform (i.e., the stimulus) was reconstructed from the spike trains by mean square estimation. 2. From the stimulus and the reconstructions we calculated the following: 1) the signal-to-noise ratio and thus an effective temporal bandwidth of the units; 2) the coding fraction, i.e., a measure of the fraction of the time-varying stimulus encoded in single spike trains; and 3) the mutual information provided by the reconstructions about the stimulus. 3. Signal-to-noise ratios as high as 7:1 were observed and the bandwidth ranged from 0 up to 200 Hz, consistent with the limit imposed by the sampling theorem. Reducing the cutoff frequency of the stimulus increased the signal-to-noise ratio at low frequencies, indicating a nonlinearity in the receptors' response. 4. The coding fraction and the rate of mutual information transmission increased in parallel with the standard deviation (i.e., the contrast) of the stimulus as well as the mean firing rate of the units. Significant encoding occurred 20-40 Hz above the spontaneous discharge of a unit. 5. When the temporal cutoff frequency of the stimulus was increased between 80 and 400 Hz, 1) the coding fraction decreased, 2) the rate of mutual information transmission remained constant over the same frequency range, and 3) the reconstructed filter changed. This is in agreement with predictions obtained in a simplified neuronal model. 6. Our results suggest that 1) the information transmitted by single spike trains of primary electrosensory afferents to higherorder neurons in the fish brain depends on the contrast and the cutoff frequency of the stimulus as well as on the mean firing rate of the units; and 2) under optimal conditions, more than half of the information about a Gaussian stimulus that can in principle be encoded is carried in single spike trains of P-type afferents at rates up to 200 bits per second.
|Additional Information:||Copyright © 1996 the American Physiological Society. Received 21 September 1995: accepted in final fonn 27 December 1995. We are indebted to the late W. Heiligenberg and to J. Spiro and C. Wong for technical assistance. The authors also thank W. Metzner for a critical reading of the manuscript. This work was supported by a grant from the National Institutes of Health to W. Heiligenberg. by a grant from the National Science Foundation, by the Center for Neuromorphic Systems Engineering as a part of the National Science Foundation Engineering Research Center Program, and by the California Trade and Commerce Agency, Office of Strategic Technology.|
|Group:||Koch Laboratory, KLAB|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||KLAB Import|
|Deposited On:||26 Jan 2008 03:44|
|Last Modified:||19 Nov 2015 00:47|
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