Age and hearing loss effects on subcortical neural encoding

项目总结 语音识别困难对于老年人和患有年龄相关性听力损失(ARHL)的人来说很常见， 尤其是在复杂的环境中。中枢听觉系统中的不良适应过度兴奋性，一种 中枢获得，已知发生在年龄和听力损失，并可能有助于改变的时间处理 以及随后的噪声中语音(SIN)缺陷。对人类中枢增益的研究通常集中在大脑皮层 多动症，然而研究表明，皮质下多动症，特别是夸大的声音编码 首音和低频调幅包络(如语音中常见的那些)可能存在于 老年人和听力受损成年人的听觉中脑，对犯罪困难的影响比 之前的想法是。然而，我们目前缺乏对皮质下 多动症存在于年龄和ARHL中，以及它与行为的关系。这使长期努力变得更加复杂 制定药物和行为干预措施以改善SIN缺陷。的首要目标是 拟议的研究是为了表征对刺激开始集和调制包络的超敏性 定位于听觉中脑(1)老年人比年轻人更常见，(2)与下位有关 丘脑结构，(3)由老年人听力损失预测(与年龄无关)，以及(4)与 罪过缺陷。实验使用了电生理学、结构神经成像和 声源定位以表征皮层下产生部位(例如下部)的神经反应 丘脑)在安静和嘈杂中。为了量化中脑相对于外周的高反应性， 下丘反应是正常的听神经反应。目标1检查多动症是否 与年轻人相比，老年人中更常见的是耳蜗压是否减少与 ARHL在安静状态下导致增强的包络编码，并评估中脑的微结构 与GABA能变化相关的特征(例如，纵向松弛时间，R1)与 对过敏症和潜在的年龄效应起调节作用。《目标2》研究了中脑超敏反应如何预测 行为，测试假设，更高的过敏性有助于在安静时的感知(例如，更好的幅度 安静时的调制(AM)辨别)，而不是噪声中的感知(例如，在SIN测试中表现较差， 噪声中的AM分辨率较差)。结果可以促进我们对信封所处环境的理解 以及皮质下听觉系统中存在的发声高反应性，如何最好地量化它，以及 无论它是有益于感知还是阻碍感知。这些发现将为未来皮质下神经的研究提供参考 多动症不仅提高了我们对老年人犯罪困难的认识，而且还决定了 临床干预需要考虑皮质下结构和功能下降的程度。与 老龄化(和听力障碍)人口逐年增长，这项研究具有很高的

PROJECT SUMMARY Speech recognition difficulties are common for older adults and those with age-related hearing loss (ARHL), particularly in complex environments. Maladaptive hyperexcitability in the central auditory system, a form of central gain, is known to occur with age and hearing loss and may contribute to altered temporal processing and subsequent speech-in-noise (SIN) deficits. Studies of central gain in humans often focus on cortical hyperactivity, yet research suggests that subcortical hyperactivity, notably exaggerated encoding of sound onsets and low-frequency amplitude modulation envelopes (like those common in speech), may be present in the auditory midbrain of older and hearing-impaired adults and exert a larger influence on SIN difficulties than previously thought. However, we currently lack a clear understanding of the contexts in which subcortical hyperactivity exists in age and ARHL and how it relates to behavior. This complicates long-term efforts to develop pharmaceutical and behavioral interventions to ameliorate SIN deficits. The overarching goal of the proposed research is to characterize how hypersensitivities to stimulus onsets and modulation envelopes localized to the auditory midbrain are (1) more prevalent for older than younger adults, (2) related to inferior colliculus structure, (3) predicted by hearing loss in older adults (independently of age), and (4) associated with SIN deficits. Experiments use an innovative combination of electrophysiology, structural neuroimaging, and source localization to characterize neural responses arising from subcortical generator sites (e.g. inferior colliculus) in both quiet and noise. To quantify hyperresponsivities in the midbrain relative to the periphery, inferior colliculus responses are normalized auditory nerve responses. Aim 1 examines whether hyperactivity is more prevalent in older adults relative to younger adults, whether diminished cochlear compression associated with ARHL leads to enhanced envelope encoding in quiet, and assesses how midbrain microstructural characteristics that have been associated with GABAergic changes (e.g. longitudinal relaxation time, R1) relate to hypersensitivity and potentially mediate age effects. Aim 2 examines how midbrain hypersensitivity predicts behavior, testing the hypothesis that greater hypersensitivity benefits perception in quiet (e.g., better amplitude modulation (AM) discrimination in quiet) but not perception in noise (e.g., poorer performance on SIN tests, poorer AM discrimination in noise). Results can advance our understanding of the contexts in which envelope and sound onset hyperresponsivities are present in the subcortical auditory system, how best to quantify it, and whether it alternately benefits or impedes perception. Findings will inform future studies of subcortical neural hyperactivity and not only improve our understanding of SIN difficulties of older adults, but also determine the extent to which clinical interventions need to consider declines in subcortical structure and function. With the aging (and hearing-impaired) population growing yearly, this research has high