ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pPP66. Neural encoding of level in the auditory nerve and anteroventral cochlear nucleus: A study of neural models and physiological responses.

M. A. Burock

L. H. Carney

Dept. of Biomed. Eng., 44 Cummington St., Boston Univ., Boston, MA 02215

Models for level discrimination based on neural counts require ``pooling'' of auditory-nerve (AN) fiber responses to explain human performance. Neither the mechanism nor site of this ``pooling'' is known. This study concerns the transformation of AN responses in the anteroventral cochlear nucleus (AVCN). An AN model with statistics consistent with physiological data [mean-to-variance ratio ((alpha))(approximately equal to)2] provided inputs to coincidence-detecting models for AVCN cells. The (alpha) of coincidence-detecting cell models is lower than the (alpha) of AN fibers. Responses of most gerbil AVCN neurons to (frozen) wideband noise had (alpha) less than 2, consistent with a coincidence-detection mechanism. The lower (alpha) implies these cells would not be as effective as AN fibers for encoding level in terms of rate. To optimally ``pool'' these responses would require either summation of a greater number of elements, or steeper rate-level curves (to compensate for lower (alpha)) and thus more elements to span a wide dynamic range. Neural coincidence detection may contribute to processing spectral information (monaurally) and localization information (binaurally). This mechanism does not provide an advantage, and perhaps introduces a disadvantage, for processing intensity information in the form of discharge rate. [Work supported by NIH, Whitaker Foundation.]