The Journal of Neurophysiology Vol. 79 No. 4 April 1998, pp. 1879-1890
Copyright ©1998 The American Physiological Society

Noise-Induced Tuning Curve Changes in Mechanoreceptors

Chandra Ivey^{1, 2}, A. Vania Apkarian^{1, 2}, and Dante R. Chialvo^{2, 3}

¹ Department of Neurosurgery and ² Computational Neuroscience Program, SUNY Health Sciences Center, Syracuse, New York 13210; and ³ Division of Neural Systems, Memory and Aging, University of Arizona, Tucson, Arizona 85724

Ivey, Chandra, A. Vania Apkarian, and Dante R. Chialvo. Noise-induced tuning curve changes in mechanoreceptors. J. Neurophysiol. 79: 1879-1890, 1998. Fibers from the tibial nerve of rat were isolated and spike activity recorded using monopolar hook electrodes. The receptive field (RF) of each recorded unit on the glabrous skin of the foot was mechanically stimulated with waveforms comprised of various frequency sine waves in addition to increasing levels of white noise. Single-unit responses were recorded for both rapidly adapting (RA) and slowly adapting (SA) units. Signal-to-noise ratio (SNR) of the output was quantified by the correlation coefficient (C₁) between the input sine wave and the nerve responses. The addition of noise enhanced signal transmission in both RA and SA fibers. With increasing noise, the initially inverted "V"-shaped, zero-noise tuning curves for RA fibers broadened and eventually inverted. There was a large expansion of the frequencies that the RA receptor responded to with increasing noise input. On the other hand, the typical shape of the SA fiber tuning curves remained invariant, at all noise levels tested. C₁ values continued to increase with larger noise input for higher frequencies, but did not do so at the lowest frequencies. For both RA and SA fibers the responses with added noise tended to be rate modulated at the low-frequency end, and followed nonlinear stochastic resonance (SR) properties at the higher frequencies. The changes in the tuning properties due to noise found here, as well as preliminary psychophysics data, imply that external noise is relevant for sensing small periodic signals in the environment. All current models of sensory perception assume that the tuning properties of receptors determined in the absence of noise are preserved during everyday tasks. Our results indicate that this is not true in a noisy environment.

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