Directionality derived from pinna-cue spectral notches in cat dorsal cochlear nucleus

Directionality derived from pinna-cue spectral notches in cat dorsal cochle ar 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 s pectral-dependent directionality than ventral cochlear nucleus (VCN) neuron s, and spectral-dependent directionality depends on response minima (nulls) produced by coincidence of best frequency (BF) and spectral-notch center f requency. Single-unit responses to 50-ms noise and tone bursts were recorde d in barbiturate-anesthetized cats (BFs: 4-37 kHz). Units were classified u sing BF tone poststimulus time histograms. Pauser, onset-G (type II interne urons), and some chopper units were recorded from the DCN. Primary-like, on set-Cn (onset other than onset-G), and most choppers in the sample were rec orded from the VCN. Many pauser and onset-G units were highly directional t o 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 d irectionality 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 B F tone, showing that the difference in noise directionality between groups depends on spectral cues. Tnese results show that spectral-dependent direct ionality is a DCN specialization. Azimuth functions of highly directional u nits exhibited response nulls, and there was a linear relationship between BFs in the range of 8-13 Wt and azimuthal locations of nulls. This relation ship parallels the known spatial distribution of spectral-notch center freq uencies on the horizontal plane. Furthermore spatial receptive fields of pa users show response nulls that follow the expected diagonal trajectory of t he spectral notch in this frequency range. These results show that DCN spec tral-dependent directionality depends on response nulls produced by coincid ence Of unit BF and spectral-notch center-frequency.