NEURAL MECHANISMS OF BINAURAL HEARING

信号到达每只耳朵的时间的不同是一个主要的 用于沿方位角定位声音的提示。两耳间的时间提示是 由用于低频信号的精细结构和由 高频、复杂信号的包络。两种不同类型耳廓的比较 时差(ITDS)始于上橄榄复合体(SOC)和 然后，进一步的处理发生在中脑、丘脑和皮质。我们 还没有检查提升中最后一个核的ITD敏感性 听觉通路，听觉皮质。对于这项拟议的项目，我们 打算填补这一空白。这些研究将在 使用细胞外单单位记录的未麻醉兔 技巧。另一个目标是确定ITD背后的电路 从SOC到皮质的敏感度。这将通过以下方式实现 向脑内注入少量逆行和顺行示踪剂 下半部ITD敏感区的生理特征 丘(IC)和皮质。 在我们对ITD敏感性的研究中，我们注意到对ITDS的调谐， 或方位接收视野大小，从 SOC连接到听觉丘脑。我们要解决的一个主要问题是，如果 是听觉皮质的进一步锐化。ITD的锐化出现了 有两种形式：要么对称地使ITD的峰值 敏感度变得更窄，或不对称地使 ITD.vs.-响应曲线变得非常陡峭，因此ITD中的一个尖锐的“边缘” 敏感性是存在的。不对称的“边缘检测器”神经元通常表现为 中间特征相。这类神经元的比例 在听觉通路的较高水平逐渐增加。这些 ITD的两种锐化形式可能会产生不同的功能 大脑皮层中声源的局部化及其数量可能会增加。 不对称的“边缘检测器”神经元群体将是最有用的 为了实现单个声源位置的准确定位， 而具有窄而对称的ITD调谐的神经元将对 解析多个声源的位置。 我们建议，在IC中看到的ITD调谐的锐化，至少在 部分，由来自同侧的输入、媒体和 侧面上橄榄。这种可能性将通过制造示踪剂来检验 注射到IC的特定ITD敏感区域，例如 主要表现为峰型、谷型或中间型反应。 我们还将确定不同地区之间的隔离和趋同 当信息从IC上升到时，ITD响应的三种类型 大脑皮层。分离可能发生在腹侧核等区域 MGB，在那里信息以相当忠诚的方式传递给 听觉皮质，而汇聚可能在媒体和 背侧区，从那里提取特定信息的神经元 可能存在不同输入的组合。 这些实验和我们之前的研究将揭示神经 ITD加工的各个水平的机制和神经底物 听觉通路。

The difference in the time of arrival of a signal at each ear is a major cue for localizing sounds along the azimuth. Interaural time cues are conveyed by the fine structure for low frequency signals and by the envelope for high frequency, Complex signals. The comparison of interaural time differences (ITDs) begins in the superior olivary complex (SOC) and further processing then occurs in the midbrain, thalamus and cortex. We have not yet examined ITD sensitivity in the last nucleus in the ascending auditory pathway, the auditory cortex. For this proposed project, we intend to fill that gap. These studies will be conducted in the unanesthetized rabbit using extracellular, single-unit recording techniques. Another aim is to determine the circuitry underlying ITD sensitivity from the SOC to the cortex. This will be accomplished by making small injections of retrograde and anterograde tracers into physiologically characterized regions of ITD sensitivity in the inferior colliculus (IC) and cortex. In our studies of ITD sensitivity, we have noted that the tuning to ITDs, or azimuthal receptive field size, becomes progressively sharper from the SOC to the auditory thalamus. A major question we will address is if there is a further sharpening at the auditory cortex. Sharpening of ITD appears to come in two forms: either symmetrically such that the peaks of ITD sensitivity becomes narrower, or asymmetrically such that one slope of the ITD.vs.-response curve becomes very steep, so that a sharp "edge" in ITD sensitivity is present. Asymmetrical, "edge-detector" neurons often show intermediate characteristic phases. The proportion of such neurons progressively increases at higher levels of the auditory pathway. These two forms of sharpening of ITD may subserve different functions useful for localizing sources of sound and their numbers may increase in the cortex. Populations of assymetrical, "edge-detector" neurons would be most useful for achieving accurate localization of a single sound source location, while neurons with narrow, symmetrical ITD-tuning would be most useful for resolving the locations of multiple sound sources. We suggest that sharpening of ITD tuning seen in the IC is, at least in part, created by the convergence of inputs from the ipsilateral, media and lateral superior olive. This possibility will be examined by making tracer injections into specific ITD sensitive regions of the IC, e.g., areas that show predominantly peak-type, trough-type, or intermediate-type responses. We will also identify regions of segregation and convergence among the three types of ITD responses as the information ascends from the IC to cortex. Segregation is expected in regions such as the ventral nucleus of the MGB, where information is relayed with considerable faithfulness to the auditory cortex, while convergence may be found in the media and dorsal divisions, where neurons that extract particular information from combinations of different inputs may exist. These experiments along with our previous studies will reveal the neural mechanisms and neural substrates for ITD processing at each level of the auditory pathway.