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The Journal of Neuroscience, April 11, 2007, 27(15):4191-4200; doi:10.1523/JNEUROSCI.5250-06.2007

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Behavioral/Systems/Cognitive
Distribution of Interaural Time Difference in the Barn Owl's Inferior Colliculus in the Low- and High-Frequency Ranges

Hermann Wagner, Ali Asadollahi, Peter Bremen, Frank Endler, Katrin Vonderschen, and Mark von Campenhausen

Institute for Biology II, Rheinisch–Westfälische Technische Hochschule Aachen, D-52074 Aachen, Germany

Correspondence should be addressed to Prof. Dr. Hermann Wagner, Institute for Biology II, Rheinisch–Westfälische Technische Hochschule Aachen, Kopernikusstrasse 16, D-52074 Aachen, Germany. Email: wagner{at}bio2.rwth-aachen.de

Interaural time differences are an important cue for azimuthal sound localization. It is still unclear whether the same neuronal mechanisms underlie the representation in the brain of interaural time difference in different vertebrates and whether these mechanisms are driven by common constraints, such as optimal coding. Current sound localization models may be discriminated by studying the spectral distribution of response peaks in tuning curves that measure the sensitivity to interaural time difference. The sound localization system of the barn owl has been studied intensively, but data that would allow discrimination between currently discussed models are missing from this animal. We have therefore obtained extracellular recordings from the time-sensitive subnuclei of the barn owl's inferior colliculus. Response peaks were broadly scattered over the physiological range of interaural time differences. A change in the representation of the interaural phase differences with frequency was not observed. In some neurons, response peaks fell outside the physiological range of interaural time differences. For a considerable number of neurons, the peak closest to zero interaural time difference was not the behaviorally relevant peak. The data are in best accordance with models suggesting that a place code underlies the representation of interaural time difference. The data from the high-frequency range, but not from the low-frequency range, are consistent with predictions of optimal coding. We speculate that the deviation of the representation of interaural time difference from optimal-coding models in the low-frequency range is attributable to the diminished importance of low frequencies for catching prey in this species.

Key words: sound localization; model; auditory; midbrain; interaural time disparity; sensory map

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Received Sept. 27, 2005; revised Feb. 6, 2007; accepted Feb. 27, 2007.

Correspondence should be addressed to Prof. Dr. Hermann Wagner, Institute for Biology II, Rheinisch–Westfälische Technische Hochschule Aachen, Kopernikusstrasse 16, D-52074 Aachen, Germany. Email: wagner{at}bio2.rwth-aachen.de

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