Directionality Derived From Pinna-Cue Spectral Notches In The Cat's Dorsal Cochlear Nucleus. Thomas J. Imig, Nikolai G. Bibikov1, Pierre Poirier2, Frank K. Samson. Department of Molecular and Integrative Physiology, Kansas University Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160-7401; 1N.N. Andreyev Acoustics Institute, Schvernik st. 4, Moscow, 117036 Russia; and 2102-165 de la Guachetiere O, Montreal, PQ, CANADA H2Z-1X6.
APStracts 6:0518N, 1999.
We tested two hypotheses to determine whether dorsal cochlear nucleus (DCN) neurons are specialized to derive directionality from spectral notches. 1. DCN neurons exhibit greater spectral-dependent directionality than ventral cochlear nucleus (VCN) neurons. 2. Spectral-dependent directionality depends on response minima (nulls) produced by coincidence of best frequency (BF) and spectral-notch center-frequency. Single unit responses to 50 ms noise and tone bursts were recorded in barbiturate anesthetized cats (BFs: 4 - 37 kHz). Units were classified using BF tone post stimulus time histograms. Pauser, onset-G (type II interneurons), and some chopper units were recorded from the DCN. Primary-like, onset-CIL (onset other than onset-G), and most choppers in the sample were recorded from the VCN. Many pauser and onset-G units were highly directional to noise. Chopper, onset-CIL, and primary-like units (collectively referred to as C-O-P units) were not. The difference in directionality depends upon a monaural mechanism as pausers were more directional to monaural noise than C-O-P units. Contralateral inhibition produced a small increase in pauser directionality to noise simulation, but had no effect on directionality of C-O-P units. Pauser and C-O-P units exhibited similar, low directionality to BF-tone showing that the difference in noise directionality between groups depends upon spectral cues. These results show that spectral-dependent directionality is a DCN specialization. Azimuth functions of highly directional units exhibited response nulls, and there was a linear relationship between BFs in the range of 8-13 kHz and azimuthal locations of nulls. This relationship parallels the known spatial distribution of spectral-notch center-frequencies on the horizontal plane. Furthermore, spatial receptive fields of pausers show response nulls that follow the expected diagonal trajectory of the spectral notch in this frequency range. These results show that DCN spectral-dependent directionality depends on response nulls produced by coincidence of unit BF and spectral-notch center-frequency.
Received 29 June 1999; accepted in final form 11 October 1999.
APS Manuscript Number J523-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999