老年性聋患者声音锁相加工障碍对言语识别的影响

Presbycusis is the major cause of hearing disability in older-adults. The reduction of speech recognition exceed the reduction of pure tone audiometry, which is one of main clinical features of presbycusis, especially in noisy condition. This manifestation suggests that there are both peripheral and central dysfunction in the auditory system. But studies on the mechanism of central auditory processing disorder in patients with presbycusis are still limited. Frequency-following responses (FFR) are sustained evoked potentials based on precisely phase-locked responses of neuron populations to low-to-middle-frequency periodical acoustical stimuli. FFR is a promising measure for studying the mechanism of speech recognition in noise for following reasons: 1.certain critical speech characteristics related to speech intelligibility are recorded; 2.FFRs to different speech sources are differentiated; 3.neural correlates of bottom-up binaural unmasking of responses to target speech are measurable; 4.neural correlates of top down unmasking of target speech are measurable. In this study, FFR will be recorded in patients with presbycusis and will be compared with those recorded in normal young adults and in patients with sensorineual hearing loss patients but not with obvious speech recognition disorder. The result will be analysised to investigate effects of phase-locking deficits on speech recognition and the mechanism of speech recognition disorder in patients with presbycusis. This study will provide more information for the speech processing mechanism in patients with presbycusis and offer basic data for future usage of FFR in clinical diagnosis of central auditory processing disorders.

老年性聋是老年人听力残疾最主要的原因，言语识别率与纯音测听不成比例地降低、噪声下言语识别障碍是其最主要的临床表现，提示老年性聋患者同时存在外周和中枢听觉功能障碍。但是其中枢听觉处理障碍机制的研究尚不充分。频率跟随反应（FFR）由那些对低-中频周期性声刺激具有准确锁相性反应的神经元发出的诱发电位组成，具有以下特征：1、能够编码言语的重要特征;2、目标言语FFR能够与掩蔽声FFR相区别;3、可反映对言语信号自下而上的双耳去掩蔽现象;4、言语信号的FFR能够被由上而下地调节。因此FFR适合用来研究噪声下言语识别障碍的机制。本研究通过在老年性聋患者中记录FFR，并与正常青年人、无言语识别障碍感音神经性听力损失患者相比较，分析老年性聋患者声音锁相加工障碍对言语识别的影响，进而分析言语识别障碍的机制。本研究将进一步明确老年性聋患者言语识别障碍的机制，并为FFR用于中枢听觉处理障碍临床诊断提供依据。

本研究内容主要分为三部分：第一部分，本研究首先对于在我院进行常规体检的老年人群中进行了听力筛查以及老年听障者调查表的研究，并对筛查阳性即达到中度听力损失及以上的患者进行宣教。结果显示老年人中存在听力损失的比例非常高，且很多已经达到中度听力损失、需要验配助听器进行干预的患者，对自己的听力损失认识不足。.第二部分，本课题组对听力正常的老年人与18至25岁的耳科正常年轻人安静环境下的言语诱发听性脑干反应的FFR进行了比较。结果显示老年组瞬态反应部分各波的潜伏期较青年组长，而FFR各波的潜伏期与青年组一致，但老年组FFR各波的振幅较青年组低；两组FFR的频谱分析显示，老年组FFR各频率共振峰的相对能量较青年组低，部分共振峰引出率较青年组低，且对于大多数共振峰，老年组FFR与刺激信号之间共振峰频率的差值较青年组大。提示与青年人相比，老年人FFR幅值低，准确性差，提示老化能够使脑干神经元对于频率信息编码能力减弱、准确性降低，这可能是造成老年性聋患者言语识别率降低的机制之一。.第三部分，本课题组分别在听力正常年轻人，听力正常老年人及老年性聋患者中进行了安静及噪声条件下的言语ABR测试研究，同时进行了噪声下言语测试。结果显示年龄影响皮层下对包络和精细结构的编码，并且在噪声条件下更明显。 老年性聋患者听敏度升高对于皮层下编码的影响主要体现在噪声环境下对于包络和精细结构平衡的失调，其中精细结构受噪声的影响与纯音听阈密切相关。噪声下言语识别与FFRENV的幅度显著相关。 根据这些发现，一方面提示皮层下对于言语包络及精细结构的编码失平衡很可能是导致老年性聋患者言语识别下降的原因之一。 另一方面也提示噪声下言语诱发听性脑干反应的有望成为评估中枢听觉处理功能的新方法。