NEURAL MECHANISMS OF BINAURAL HEARING

信号到达每只耳朵的时间差异是一个主要的问题。 用于沿方位角沿着定位声音的提示。耳间时间线索是 低频信号由精细结构传送， 高频、复杂信号的包络。耳间比较 时间差（ITD）开始于上级橄榄复合体（SOC）， 然后在中脑、丘脑和皮层中进行进一步的处理。我们 我还没有检查ITD的敏感性，在最后一个核在上升 听觉通路，听觉皮层。对于这个项目，我们 打算填补这一空白。这些研究将在 非麻醉家兔，使用细胞外，单单位记录 技术.另一个目的是确定ITD的潜在电路 从SOC到皮质的敏感性。这将通过 将逆行和顺行示踪剂注入 下丘脑ITD敏感性的生理特征区域 丘（IC）和皮质。 在我们对ITD敏感性的研究中，我们注意到调谐到ITD， 或方位角感受野大小，变得越来越尖锐， 听觉丘脑的SOC。我们要解决的一个主要问题是， 是听觉皮层的进一步强化ITD的锐化出现 以两种形式出现：或者对称地使得ITD的峰 灵敏度变得更窄或不对称，使得 ITD与-响应曲线变得非常陡峭，因此ITD中的尖锐“边缘” 敏感性存在。不对称的“边缘探测器”神经元经常显示 中间特征阶段。这种神经元的比例 在听觉通路的更高水平上逐渐增加。这些 ITD的两种形式的锐化可以有助于不同的功能， 定位声源及其数量可能在皮层中增加。 非对称的“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精确定位， 而具有窄的、对称的ITD调谐的神经元将是最有用的， 解析多个声源的位置。 我们认为，在IC中看到的ITD调谐的锐化，至少在 部分，由来自同侧、媒体和 外侧上级橄榄体。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，的领域 主要表现为峰型、谷型或中间型响应。 我们还将确定区域之间的隔离和收敛 三种类型的ITD响应，因为信息从IC上升到 皮层分离预计在区域，如腹核的 MGB，在那里，信息被相当忠实地传递给 听觉皮层，而会聚可以在媒体中找到， 神经元在这里从大脑中提取特定的信息， 可以存在不同输入的组合。 这些实验沿着我们以前的研究将揭示神经 ITD处理的机制和神经基质在每个级别的 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.