Section of Neurobiology, 337 Patterson Laboratory Building, The University of Texas at Austin, Austin, TX 78712, USA.
Hear Res. 2012 Jun;288(1-2):47-57. doi: 10.1016/j.heares.2012.01.011. Epub 2012 Feb 8.
Interaural intensity disparities (IIDs), the cues all animals use to localize high frequency sounds, are initially processed in the lateral superior olive (LSO) by a subtractive process where inputs from one ear excite and inputs from the other ear inhibit LSO neurons. Such cells are called excitatory-inhibitory (EI) neurons and are prominent not only in the LSO but also in higher nuclei, which include the dorsal nucleus of the lateral lemniscus (DNLL) and inferior colliculus (IC). The IC is of particular interest since its EI cells receive diverse innervation patterns from a large number of lower nuclei, which include the DNLLs and LSOs, and thus comprise a population with diverse binaural properties. The first part of this review focuses on the circuits that create EI cells in the LSO, DNLL and IC. The second section then turns to the responses evoked by dynamic IIDs that change over time, as with multiple sounds that emanate from different regions of space or moving sound sources. I show that many EI neurons in the IC respond to dynamic IIDs in ways that are not predictable from their responses to static IIDs, IIDs presented one at a time. In the final section, results from in vivo whole cell recording in the IC are presented and address the connectional basis for the responsiveness to dynamic IIDs. The principal conclusion is that EI cells comprise a diverse population. The diversity is created by the particular set of inputs each EI type receives and is expressed in the differences in the responses to dynamic IIDs that are generated by those inputs. These results show that the construction of EI neurons in the IC imparts features that not only encode the location of an individual sound source, but also that allow animals to determine the direction of a moving sound and to focus and localize a single sound in midst of many sounds, as typically occurs in the daily lives of all animals.
两耳强度差（IIDs）是所有动物用来定位高频声音的线索，最初在外侧上橄榄核（LSO）中通过一个减法过程进行处理，其中一只耳朵的输入兴奋，另一只耳朵的输入抑制 LSO 神经元。这种细胞被称为兴奋-抑制（EI）神经元，不仅在 LSO 中很突出，而且在更高的核中也很突出，包括外侧丘系背核（DNLL）和下丘（IC）。IC 特别有趣，因为它的 EI 细胞接收来自大量低级核的不同传入模式，包括 DNLL 和 LSO，因此构成了一个具有不同双耳特性的群体。这篇综述的第一部分重点介绍了在 LSO、DNLL 和 IC 中产生 EI 细胞的回路。第二部分然后转向了由随时间变化的动态 IIDs 引起的反应，就像来自空间不同区域或移动声源的多个声音一样。我表明，IC 中的许多 EI 神经元对动态 IIDs 的反应方式与对静态 IIDs 的反应方式不同，静态 IIDs 一次呈现一个。在最后一节中，呈现了在 IC 中进行的体内全细胞记录的结果，并解决了对动态 IIDs 反应的连接基础。主要结论是 EI 细胞构成了一个多样化的群体。这种多样性是由每个 EI 类型接收的特定输入集创建的，并体现在由这些输入生成的对动态 IIDs 的反应差异中。这些结果表明，IC 中 EI 神经元的构建赋予了不仅可以编码单个声源位置的特征，还可以使动物确定移动声源的方向，并在许多声音中聚焦和定位单个声音，这在所有动物的日常生活中通常会发生。
