Cellular Mechanisms Underlying Sound Localization

描述（由申请人提供）：听觉系统显示的微秒时间精度对于声音的定位和解码至关重要。这项资助研究了编码和处理仓鸮、其他鸟类和爬行动物的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，它投射到层状核，在那里首先计算耳间时差（ITDs）。由于层状核输入中的精确时间编码对于检测过渡段至关重要，因此我们将确定锁相在电路发展过程中如何变化。这些研究将与髓鞘形成调控的研究同时进行，髓鞘形成对时间编码也是必不可少的。过渡段神经编码的性质是有争议的，目前的模型要么支持类似地图的过渡段位置编码，与仓鸮的数据一致，要么支持基于率的种群编码，与小型哺乳动物的数据一致。我们将在鸡身上测试这些理论，鸡的头部大小和相位锁定与小型哺乳动物相似，以解决ITD的神经编码策略。好的过渡段检测需要什么？在鸟类和哺乳动物中，ITD编码神经元通常具有双极性形态，来自每只耳朵的输入被分离到树突树上。由于这种分离改善了建模研究中的过渡段编码，我们将使用体外分析来寻找重合检测器神经元中预测的树突非线性。仓鸮的声音定位比鸡的更准确。我们将使用体内记录来确定这是由于计算能力（即更多的神经元致力于特定的ITD计算）和/或单个神经元反应的特定改进。耳蜗角核与哺乳动物耳蜗核在生理反应上的相似性表明，专门编码听觉刺激相关特征的细胞存在趋同进化。比较鸟类和哺乳动物CN的编码，可以让我们识别上行听觉流中神经编码的显著特征，并显示反应类型是如何出现的。

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.