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The Journal of Neurophysiology Vol. 83 No. 2 February 2000, pp. 907-925
Copyright ©2000 by the American Physiological Society
Department of Molecular and Integrative Physiology, Kansas University Medical Center, Kansas City, Kansas 66160-7401
Imig, Thomas J.,
Nikolai G. Bibikov,
Pierre Poirier, and
Frank K. Samson.
Directionality Derived From Pinna-Cue Spectral Notches in Cat
Dorsal Cochlear Nucleus. J. Neurophysiol. 83: 907-925, 2000. We tested two hypotheses to determine whether
dorsal cochlear nucleus (DCN) neurons are specialized to derive
directionality from spectral notches: DCN neurons exhibit greater
spectral-dependent directionality than ventral cochlear nucleus (VCN)
neurons, and 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 poststimulus 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 on 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 on 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.
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