Cellular Mechanisms Underlying Sound Localization

描述（由申请人提供）：听觉系统显示的微秒级时间精度对于声音的定位和解码至关重要。这项研究旨在研究仓鸮和其他鸟类和爬行动物编码和处理时间信息的神经回路，以确定听觉编码的共同特征。时间信息在耳蜗大细胞核中处理，该核投射到板状核，在板状核中首先计算耳间时间差（ITD）。由于精确的时间编码的输入到核板是至关重要的ITDs的检测，我们将确定如何锁相电路的发展过程中的变化。这些研究将与髓鞘形成的调节研究平行进行，髓鞘形成对于时间编码也是必不可少的。ITD的神经代码的性质是有争议的，目前的模型主张ITD的地图式位置代码，与仓鸮的数据一致，或基于速率的人口代码，与小型哺乳动物的数据一致。我们将在鸡中测试这些理论，鸡与小型哺乳动物具有相似的头部大小和相位锁定，以解决ITD的神经编码策略。良好的ITD检测需要什么？在鸟类和哺乳动物中，ITD编码神经元通常具有双极形态，来自每个耳朵的输入被分离到树突树上。由于这种隔离提高了ITD编码的建模研究，我们将使用体外分析，以寻找预测的树突状非线性重合检测神经元。仓鸮的声音定位比鸡更准确。我们将使用体内记录来确定这是否是由于计算能力（即更多的神经元致力于特定的ITD计算）和/或个别神经元的反应的具体改善。耳蜗角核和哺乳动物耳蜗核的生理反应的相似性表明，有专门用于编码听觉刺激的相关功能的细胞的趋同进化。鸟类和哺乳动物CN编码的比较应该使我们能够识别上升听觉流中神经代码的显著特征，并显示反应类型如何出现。

DESCRIPTION (provided by applicant): The microsecond temporal precision shown by auditory systems is essential for location and decoding of sound. This grant examines the neural circuits that encode and process temporal information in the barn owl and other birds and reptiles in order to identify shared general features of auditory coding. Temporal information is processed in the cochlear nucleus magnocellularis, which projects to the nucleus laminaris, where interaural time differences (ITDs) are first computed. Since precise temporal coding in the inputs to the nucleus laminaris is critical to the detection of ITDs, we will determine how phase-locking changes during circuit development. These studies will be carried out in parallel with studies of the regulation of myelination, which is also essential for temporal coding. The nature of the neural code for ITD is controversial, with current models advocating either a map-like place code for ITD, consistent with data in the barn owl, or a rate-based population code, consistent with data from small mammals. We will test these theories in the chicken, which has a similar head size and phase locking as small mammals, to address the neural coding strategies for ITD. What is needed for good ITD detection? ITD coding neurons generally possess bipolar morphology in both birds and mammals, with inputs from each ear segregated onto dendritic trees. Since this segregation improves ITD coding in modeling studies, we will use in vitro analyses to look for the predicted dendritic non-linearities in coincidence detector neurons. The barn owl's sound localization is more accurate than a chicken's. We will use in vivo recordings to determine if this is due to computational power (i.e. more neurons devoted to a particular ITD computation) and/or to specific improvements in the responses of individual neurons. The similarity in physiological responses in the cochlear nucleus angularis and mammalian cochlear nucleus suggests there is convergent evolution of cells specialized for encoding relevant features of the auditory stimulus. Comparisons of coding in bird and mammal CN should allow us to identify salient features of the neural codes in the ascending auditory stream, and show how response types emerge.