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The Journal of Neuroscience, September 3, 2003, 23(22):8143-8151

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GABA Is Involved in Spatial Unmasking in the Frog Auditory Midbrain

Wen-Yu Lin and Albert S. Feng

Department of Molecular and Integrative Physiology and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

Real-world listening situations comprise multiple auditory objects. Sounds originating from different objects are summated at the eardrum. The auditory system therefore must segregate the streams of sounds associated with the different objects. One listening strategy in complex environments is to attend to signals originating from one spatial location. In doing so, signal detection is compromised when a masker is present at close proximity, and detection is improved if the masker is spatially separated from the signal. A recent study has shown that, in frogs, spatial unmasking is more robust at the midbrain than at the periphery, indicating the importance of central mechanisms for this process. In this study, we investigated spatial unmasking patterns of single neurons in the frog inferior colliculus (IC) before and during iontophoretic application of bicuculline, a GABA_A receptor antagonist. We found that drug application markedly decreased the strength of spatial unmasking such that even large angular separation of signal and masker sources produced only a weak masking release. Under the drug, the strength of spatial unmasking of midbrain neurons approximated that of auditory nerve fibers. These data show that GABAergic interactions in the auditory midbrain play an important role in spatial unmasking. Analysis of the effect of the drug on the direction sensitivity of the units shows that for the majority of IC units, bicuculline degrades binaural processing involved in directional coding, thereby compromising spatial unmasking. For other IC units, however, the decline in the strength of spatial unmasking is attributable to the effects of bicuculline on different central auditory processes.

Key words: inferior colliculus; torus semicircularis; stream segregation; release from masking; spatial unmasking; bicuculline; hearing; masking; signal detection

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Received April 10, 2003; revised June 23, 2003; accepted June 30, 2003.

This article has been cited by other articles:

				A. V. Galazyuk, W. Lin, D. Llano, and A. S. Feng Leading Inhibition to Neural Oscillation Is Important for Time-Domain Processing in the Auditory Midbrain J Neurophysiol, July 1, 2005; 94(1): 314 - 326. [Abstract] [Full Text] [PDF]

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