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. 2002 Dec 4;4(2):148–163. doi: 10.1007/s10162-002-2002-5

Auditory Processing of Spectral Cues for Sound Localization in the Inferior Colliculus

Kevin A Davis 1, Ramnarayan Ramachandran 1, Bradford J May 2,✉
PMCID: PMC3202719  PMID: 12943370

Abstract

The head-related transfer function (HRTF) of the cat adds directionally dependent energy minima to the amplitude spectrum of complex sounds. These spectral notches are a principal cue for the localization of sound source elevation. Physiological evidence suggests that the dorsal cochlear nucleus (DCN) plays a critical role in the brainstem processing of this directional feature. Type O units in the central nucleus of the inferior colliculus (ICC) are a primary target of ascending DCN projections and, therefore, may represent midbrain specializations for the auditory processing of spectral cues for sound localization. Behavioral studies confirm a loss of sound orientation accuracy when DCN projections to the inferior colliculus are surgically lesioned. This study used simple analogs of HRTF notches to characterize single-unit response patterns in the ICC of decerebrate cats that may contribute to the directional sensitivity of the brain's spectral processing pathways. Manipulations of notch frequency and bandwidth demonstrated frequency-specific excitatory responses that have the capacity to encode HRTF-based cues for sound source location. These response patterns were limited to type O units in the ICC and have not been observed for the projection neurons of the DCN. The unique spectral integration properties of type O units suggest that DCN influences are transformed into a more selective representation of sound source location by a local convergence of wideband excitatory and frequency-tuned inhibitory inputs.

Keywords: sound localization, head-related transfer function, dorsal cochlear nucleus, central nucleus, spectral integration

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Acknowledgements

E. Young contributed archival data from his previous studies of the dorsal cochlear nucleus. This work was supported by National Institute of Deafness and Other Communication Disorders grant 5R01DC00954. Pharmacological manipulations were performed in conjunction with NIDCD grant 1R03DC03758.

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