Cellular Mechanisms Underlying Sound Localization

描述(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是必不可少的。这项授权研究了谷仓、猫头鹰和其他鸟类和爬行动物中编码和处理时间信息的神经电路，以确定听觉编码的共同一般特征。时间信息是在耳蜗核的大细胞中处理的，它投射到板层核，在那里首先计算耳间时间差(ITDS)。由于板核输入的精确时间编码对于检测ITDS至关重要，我们将确定锁相在电路发展过程中是如何变化的。这些研究将与髓鞘形成的调节研究并行进行，髓鞘形成的调节对时间编码也是必不可少的。ITD的神经编码的性质是有争议的，目前的模型要么主张ITD的地图式位置编码，与谷仓猫头鹰的数据一致，要么主张基于比率的种群编码，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。做好ITD检测需要做些什么？在鸟类和哺乳动物中，ITD编码神经元通常具有两极形态，每只耳朵的输入被分离到树突树上。由于这种分离改进了建模研究中的ITD编码，我们将使用体外分析来寻找符合探测器神经元中预测的树突非线性。谷仓猫头鹰的声音定位比鸡的更准确。我们将使用活体录音来确定这是否归因于计算能力(即更多的神经元致力于特定的ITD计算)和/或单个神经元的反应的特定改进。耳蜗核、角状核和哺乳动物耳蜗核的生理反应具有相似性，提示有专门编码听觉刺激相关特征的细胞的趋同进化。鸟类和哺乳动物CN的编码比较应该允许我们识别上升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.