Larsen Ole Næsbye, Christensen-Dalsgaard Jakob, Jensen Kenneth Kragh
Department of Biology, University of Southern Denmark, Campusvej 55, 5230, Odense, Denmark.
Starkey Hearing Technologies, 6600 Washington Ave. S, Eden Prairie, MN, 55344, USA.
Biol Cybern. 2016 Oct;110(4-5):319-331. doi: 10.1007/s00422-016-0688-4. Epub 2016 May 21.
Whereas it is clear from anatomical studies that all birds have complex interaural canals connecting their middle ears, the effect of interaural coupling on directional hearing has been disputed. A reason for conflicting results in earlier studies may have been that the function of the tympanic ear and hence of the interaural coupling is sensitive to variations in the intracranial air pressure. In awake birds, the middle ears and connected cavities are vented actively through the pharyngotympanic tube. This venting reflex seems to be suppressed in anesthetized birds, leading to increasingly lower pressure in the interaural cavities, stiffening the eardrums, and displacing them medially. This causes the sensitivity, as well as the interaural coupling, to drop. Conversely, when the middle ears are properly vented, robust directional eardrum responses, most likely caused by internal coupling, have been reported. The anatomical basis of this coupling is the 'interaural canal,' which turns out to be a highly complex canal and cavity system, which we describe for the zebra finch. Surprisingly, given the complexity of the interaural canals, simple models of pipe-coupled middle ears fit the eardrum directionality data quite well, but future models taking the complex anatomy into consideration should be developed.
尽管解剖学研究清楚地表明，所有鸟类都有连接中耳的复杂耳内通道，但耳内耦合对定向听觉的影响一直存在争议。早期研究结果相互矛盾的一个原因可能是，鼓室耳的功能以及耳内耦合对颅内气压变化很敏感。在清醒的鸟类中，中耳和相连的腔室通过咽鼓管进行主动通气。这种通气反射在麻醉的鸟类中似乎受到抑制，导致耳内腔室压力越来越低，使鼓膜变硬并向内移位。这会导致灵敏度以及耳内耦合下降。相反，当中耳通气良好时，已经报道了鼓膜对方向的强烈反应，这很可能是由内部耦合引起的。这种耦合的解剖学基础是“耳内通道”，它原来是一个高度复杂的通道和腔室系统，我们将对斑胸草雀的这种系统进行描述。令人惊讶的是，考虑到耳内通道的复杂性，简单的管道耦合中耳模型与鼓膜方向性数据拟合得相当好，但未来应开发考虑到复杂解剖结构的模型。
