Peña J L, Konishi M
Division of Biology 216-76, California Institute of Technology, Pasadena, CA 91125, USA.
Proc Natl Acad Sci U S A. 2000 Oct 24;97(22):11787-92. doi: 10.1073/pnas.97.22.11787.
Both mammals and birds use the interaural time difference (ITD) for localization of sound in the horizontal plane. They may localize either real or phantom sound sources, when the signal consists of a narrow frequency band. This ambiguity does not occur with broadband signals. A plot of impulse rates or amplitude of excitatory postsynaptic potentials against ITDs (ITD curve) consists of peaks and troughs. In the external nucleus (ICX) of the owl's inferior colliculus, ITD curves show multiple peaks when the signal is narrow-band, such as tones. Of these peaks, one occurs at ITDi, which is independent of frequency, and others at ITDi +/- T, where T is the tonal period. The ITD curve of the same neuron shows a large peak (main peak) at ITDi and no or small peaks (side peaks) at ITDi +/- T, when the signal is broadband. ITD curves for postsynaptic potentials indicate that ICX neurons integrate the results of binaural cross-correlation in different frequency bands. However, the difference between the main and side peaks is small. ICX neurons further enhance this difference in the process of converting membrane potentials to impulse rates. Inhibition also appears to augment the difference between the main and side peaks.
哺乳动物和鸟类都利用双耳时间差（ITD）在水平面内对声音进行定位。当信号由窄频带组成时，它们可以对真实或虚拟声源进行定位。对于宽带信号，这种模糊性不会出现。兴奋性突触后电位的冲动率或幅度相对于ITD的曲线图（ITD曲线）由峰和谷组成。在猫头鹰下丘的外侧核（ICX）中，当信号为窄带时，如纯音，ITD曲线显示多个峰。在这些峰中，一个出现在ITDi，它与频率无关，其他峰出现在ITDi +/- T，其中T是音调周期。当信号为宽带时，同一神经元的ITD曲线在ITDi处显示一个大峰（主峰），在ITDi +/- T处没有或只有小峰（边峰）。突触后电位的ITD曲线表明，ICX神经元整合了不同频带双耳互相关的结果。然而，主峰和边峰之间的差异很小。ICX神经元在将膜电位转换为冲动率的过程中进一步增强了这种差异。抑制作用似乎也增加了主峰和边峰之间的差异。
