Berlin C I, Hood L J, Cecola R P, Jackson D F, Szabo P
Kresge Hearing Research Laboratory of the South, Department of Otorhinolaryngology, Louisiana State University Medical Center, New Orleans 70112.
Hear Res. 1993 Feb;65(1-2):40-50. doi: 10.1016/0378-5955(93)90199-b.
We present here two patients and three control subjects to demonstrate the clinical utility of studying evoked otoacoustic emissions and their contralateral suppression, as an aid to the delineation of afferent neuron dysfunction and possible lack of efferent suppression. The key patients here who fail to show contralateral suppression of their very robust otoacoustic emissions, concomitantly show paradoxically absent auditory brainstem responses (ABRs) and absence of middle ear muscle reflexes despite normal audiograms in the 2 kHz region and normal tympanograms. One of these patients has nearly normal pure tone sensitivity up to 3 kHz. The other has normal sensitivity in the 2 kHz region, but poor sensitivity on either side of that frequency. In addition, the two patients of interest show absent masking level differences and inordinately poor speech discrimination. Three 'foils' are presented: one patient with poor hearing on either side of 2 kHz, one with Bell's Palsy, and the third with bilateral temporal lobe disease. These patients show respectively that (1) isolated normal hearing at 2 kHz, (2) absence of middle ear muscle reflexes and (3) conscious cortical awareness of sound do not contribute directly to this intriguing clinical state. We propose that these patients with absent ABRs suffer from an auditory nervous system dysfunction which disrupts access to the efferent system. This condition also disables whatever systems contribute to the neural synchrony inherent in recording compound far-field action potentials such as the ABR. There are a number of hypotheses to be considered here. One suggests that the key patients are deficient in synchronous activation of Type I afferent fibers to the degree that they cannot activate efferent feedback, or they may be able to use only so-called Type II afferent neurons to support their normal zones of pure tone sensitivity. A less likely consideration focuses on the notion that discharge of primary neurons might be in some way synchronized by an efferent system which in these patients is the primary source of deficit.
我们在此展示两名患者和三名对照受试者，以证明研究诱发耳声发射及其对侧抑制在临床上的实用性，这有助于明确传入神经元功能障碍以及可能存在的传出抑制缺失情况。此处的关键患者，其非常强烈的耳声发射未能表现出对侧抑制，同时令人费解的是，尽管在2kHz区域听力图正常且鼓室图正常，但听觉脑干反应（ABR）缺失且中耳肌反射消失。其中一名患者在高达3kHz时纯音敏感度几乎正常。另一名患者在2kHz区域敏感度正常，但在该频率两侧敏感度较差。此外，这两名相关患者的掩蔽级差缺失，言语辨别能力极差。还展示了三名“对照者”：一名在2kHz两侧听力均差的患者，一名患有贝尔氏面瘫的患者，以及第三名患有双侧颞叶疾病的患者。这些患者分别表明：（1）2kHz处孤立的正常听力，（2）中耳肌反射缺失，（3）对声音的有意识皮层感知并不会直接导致这种引人关注的临床状态。我们认为，这些ABR缺失的患者患有听觉神经系统功能障碍，该障碍扰乱了对传出系统的接入。这种情况还使任何有助于记录复合远场动作电位（如ABR）所固有的神经同步性的系统失效。这里有许多假设需要考虑。一种假设认为，关键患者的I型传入纤维同步激活不足，以至于无法激活传出反馈，或者他们可能只能使用所谓的II型传入神经元来维持其正常的纯音敏感区域。一个不太可能的考虑点是，初级神经元的放电可能在某种程度上由一个传出系统同步，而在这些患者中，该传出系统是缺陷的主要来源。
