STRUCTURAL BASIS OF CENTRAL HEARING MECHANISMS

（摘自申请人摘要） 本提案的目的是 确定中枢听觉通路的结构组织， 处理双耳信息。 传入神经的功能类型 投射到下丘中央核的神经元数目较少， 不同的，可能是单一的IC神经元整合信息 从许多传入的来源。 目前没有足够的信息 这些传入神经的组织来决定它们的贡献 感受野特性和其他反应特性 双耳细胞 一种假设是轴突的分布和形态 在等频率平面内是不均匀的。 因此，许多不同的 传入神经的组合会汇聚在突触区， 对这些区域细胞的反应特性。 第二个假设是 传入神经等频区的相对空间关系 细胞核是由组织的投影保存到 下丘 拓扑结构将提供一个位置代码， 双耳特征 为了解决有关这两个假设的问题，一系列实验 详细描述了下丘脑的传入神经连接 成年猫的丘。 具体目标是：（1）确定 内侧上级传入纤维片和单轴突的几何形状 橄榄投射到IC使用散装和单一轴突顺行 追踪方法; 2）比较会聚轴突系统的几何形状 与MSO轴突的组织一起使用共同标记的方法 在同一段中来自一个以上来源的预测;以及3） 将轴突内标记的轴突的分布和形态与 电生理识别细胞的响应特性 将轴突发送到IC。 这些结果将导致进一步的假设， 轴突相互作用的组织及其与双耳 在IC中处理。 双耳处理对于声音来说很重要 语音的复杂特征的定位、编码以及 例如掩蔽和信号检测等现象。 改进对 听力受损个体的这些功能需要实验， 正如一个提议增加我们的解剖学知识， 神经处理声音的生理基础。

(Adapted from the Applicant's Abstract.) The goal of this proposal is to determine the structural organization of central auditory pathways that process binaural information. The functional types of afferents that project to the central nucleus of the inferior colliculus are quite diverse and it is possible that single IC neurons integrate information from many afferent sources. At present there is insufficient information about the organization of these afferents to determine their contribution to receptive field properties and other response characteristics of binaural cells. One hypothesis is that axonal distribution and morphology are heterogeneous within iso-frequency planes. Thus, many different combinations of afferents would converge in synaptic zones and contribute to response properties of cells in those zones. A second hypothesis is that relative spatial relationships in iso-frequency regions of afferent nuclei are preserved by the organization of the projections to the inferior colliculus. The topology would provide a place code for binaural features. To address questions regarding the two hypotheses, a series of experiments detailing the organization of the afferent connections to the inferior colliculus in the adult cat are proposed. Specific aims are: 1) to define the geometry of the afferent sheets and single axons of medial superior olivary projections to the IC using bulk and single axonal anterograde tracing methods; 2) to compare the geometry of converging axonal systems with the organization of the MSO axons with methods to co-label projections from more than one source in the same sections; and 3) to relate the distribution and morphology of intra-axonally labeled axons to response characteristics of electrophysiologically identified cells sending axons to IC. The results will lead to further hypotheses about the organization of axonal interactions and their relationship to binaural processing in the IC. Binaural processing is important for sound localization, coding of complex features of speech sounds and for phenomena such as masking and signal detection. Improving assessment of these functions in hearing impaired individuals requires experiments such as the one proposed to increase our knowledge about the anatomical and physiological basis for neural processing of sound.