Sound-intensity-dependent compensation for the small interaural time difference cue for sound source localization.
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 (> or =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.
Nishino
Eri
E
Departments of Physiology and Morphological Brain Science, Faculty of Medicine, Kyoto University, Kyoto 606-8501, Japan.
Yamada
Rei
R
Kuba
Hiroshi
H
Hioki
Hiroyuki
H
Furuta
Takahiro
T
Kaneko
Takeshi
T
Ohmori
Harunori
H
D000161:Acoustic Stimulation / Q000379:methods; D000200:Action Potentials / Q000502:physiology; D000222:Adaptation, Physiological / Q000502:physiology*; D000367:Age Factors; D000818:Animals; D001306:Auditory Pathways / Q000378:metabolism / Q000502:physiology; D001309:Auditory Threshold / Q000502:physiology; D001522:Behavior, Animal; D002645:Chickens; D003198:Computer Simulation; D003463:Cues; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology / Q000528:radiation effects; D007839:Functional Laterality; D007266:Inhibition, Psychological; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism; D018408:Patch-Clamp Techniques / Q000379:methods; D011601:Psychophysics; D011930:Reaction Time / Q000502:physiology*; D013016:Sound; D013017:Sound Localization / Q000502:physiology*; D013997:Time Factors; D050495:Vesicular Inhibitory Amino Acid Transport Proteins / Q000378:metabolism
D009687:Nuclear Proteins; D050495:Vesicular Inhibitory Amino Acid Transport Proteins; C493406:vesicular GABA transporter