Effects of Conductive Hearing Loss on Neural Mechanisms of Binaural Hearing

单侧传导性听力损失(CHL)在发育过程中会导致包括声音定位在内的听觉功能的长期缺陷。这些缺陷发生的解剖学和生理学机制以及发生的时间还不是很清楚。双耳听力发育的敏感期被认为是为了适应由于头部和耳廓生长而导致的位置的声学线索的变化。虽然可塑性可能允许对线索的神经回路进行校准，但它也可能适应由CHL引起的不适当的线索。我们的目标是了解在听力正常的动物和从出生就患有CHL的动物身上，位置线索和编码它们的电路是如何同时发展的。这项建议的主要重点是研究听觉正常的成年动物和出生时就有轻度至中度单侧CHL的成年动物的耳间电平差异(ILD)线索对声音位置的编码。在具体目标1中，细胞外记录(包括单单位和多单位)将用于研究下丘中央核(ICC)神经元的单耳和双耳反应特性。ICC是上行听觉通路中的一个中脑核团，从脑干核团接收传入输入，最初将提示编码到声音位置。这一目的检验了特定的假设，即ILD敏感的ICC神经元的声学编码能力发生变化，以补偿单侧CHL导致的ILD线索的改变。为了验证这一假设，我们将测量纯音和噪声刺激对ILD的敏感度，并在正常听力提示条件和模拟CHL的虚拟耳塞条件下，测量单耳和双耳刺激的虚拟空间感受野。具体目标2探讨了中耳积液(渗出)导致的CHL如何影响位置、耳间时间和水平差异以及单耳频谱形状线索的整个集合。

Unilateral conductive hearing loss (CHL) during development can produce long-term deficits in auditory functions including sound localization. The anatomical and physiological mechanisms responsible for and the time period over which these deficits occur are not well understood. A sensitive period for the development of binaural hearing is hypothesized to accommodate changes in the acoustical cues to location due to head and pinnae growth. While plasticity may allow calibration of neural circuits to the cues, it may also adapt to inappropriate cues resulting from CHL. The goals are to understand the concurrent development of the cues to location and the circuits that encode them in animals with normal hearing and those reared from birth with CHL. The primary focus of this proposal is to study the encoding of the interaural level difference (ILD) cue to sound location in adult animals with normal hearing and those that have had a mild to moderate unilateral CHL present from birth. In Specific Aim 1, extracellular recordings (both single- and multi-unit) will be used to study the monaural and binaural response properties of neurons in the central nucleus of the inferior colliculus (ICC), a midbrain nucleus in the ascending auditory pathway that receives afferent inputs from the brainstem nuclei that initially encode the cues to sound location. This aim tests the specific hypothesis that the acoustic coding capabilities of ILD-sensitive ICC neurons change in order to compensate for the altered ILD cues that result as a consequence of the unilateral CHL. To test this hypothesis, ILD sensitivity will be measured for pure-tone and noise stimuli and virtual space receptive fields will be measured for monaural and binaural stimulation under both normal hearing cue conditions and a "virtual earplug" condition that simulates those due to CHL. Specific Aim 2 explores how CHL due to fluid buildup in the middle ear (effusion) affects the entire ensemble of acoustic cues to location, the interaural time and level differences and the monaural spectral shape cues.