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The Journal of Neuroscience, July 9, 2008, 28(28):7153-7164; doi:10.1523/JNEUROSCI.4398-07.2008

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Behavioral/Systems/Cognitive
Sound-Intensity-Dependent Compensation for the Small Interaural Time Difference Cue for Sound Source Localization

Eri Nishino,¹ Rei Yamada,¹ Hiroshi Kuba,¹ Hiroyuki Hioki,² Takahiro Furuta,² Takeshi Kaneko,² and Harunori Ohmori¹

Departments of ¹Physiology and ²Morphological Brain Science, Faculty of Medicine, Kyoto University, Kyoto 606-8501, Japan

Correspondence should be addressed to Harunori Ohmori at the above address. Email: ohmori{at}nbiol.med.kyoto-u.ac.jp

Interaural time difference (ITD) is a major cue for sound source localization. However, animals with small heads experience small ITDs, making ITD detection difficult, particularly for low-frequency sound. Here, we describe a sound-intensity-dependent mechanism for compensating for the small ITD cues in the coincidence detector neurons in the nucleus laminaris (NL) of the chicken aged from 3 to 29 d after hatching. The hypothesized compensation mechanisms were confirmed by simulation. In vivo single-unit recordings revealed an improved contrast of ITD tuning in low-best-frequency (<1 kHz) NL neurons by suppressing the firing activity at the worst ITD, whereas the firing rate was increased with increasing sound intensity at the best ITD. In contrast, level-dependent suppression was so weak in the middle- and high-best-frequency (1 kHz) NL neurons that loud sounds led to increases in firing rate at both the best and the worst ITDs. The suppression of firing activity at the worst ITD in the low-best-frequency neurons required the activation of the superior olivary nucleus (SON) and was eliminated by electrolytic lesions of the SON. The frequency-dependent suppression reflected the dense projection from the SON to the low-frequency region of NL. Thus, the small ITD cues available in low-frequency sounds were partly compensated for by a sound-intensity-dependent inhibition from the SON.

Key words: sound localization; interaural time difference; nucleus laminaris; nucleus magnocellularis; coincidence detection; superior olivary nucleus

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Received Sept. 26, 2007; revised May 28, 2008; accepted June 6, 2008.

Correspondence should be addressed to Harunori Ohmori at the above address. Email: ohmori{at}nbiol.med.kyoto-u.ac.jp

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