Oertel D
Department of Physiology, University of Wisconsin, Madison 53706, USA.
Annu Rev Physiol. 1999;61:497-519. doi: 10.1146/annurev.physiol.61.1.497.
Vertebrate animals gain biologically important information from environmental sounds. Localization of sound sources enables animals to detect and respond appropriately to danger, and it allows predators to detect and localize prey. In many species, rapidly fluctuating sounds are also the basis of communication between conspecifics. This information is not provided directly by the output of the ear but requires processing of the temporal pattern of firing in the tonotopic array of auditory nerve fibers. The auditory nerve feeds information through several parallel ascending pathways. Anatomical and electrophysiological specializations for conveying precise timing, including calyceal synaptic terminals and matching axonal conduction times, are evident in several of the major ascending auditory pathways through the ventral cochlear nucleus and its nonmammalian homologues. One pathway that is shared by all higher vertebrates makes an ongoing comparison of interaural phase for the localization of sound in the azimuth. Another pathway is specifically associated with higher frequency hearing in mammals and is thought to make use of interaural intensity differences for localizing high-frequency sounds. Balancing excitation from one ear with inhibition from the other in rapidly fluctuating signals requires that the timing of these synaptic inputs be matched and constant for widely varying sound stimuli in this pathway. The monaural nuclei of the lateral lemniscus, whose roles are not understood (although they are ubiquitous in higher vertebrates), receive input from multiple pathways that encode timing with precision, some through calyceal endings.
脊椎动物从环境声音中获取具有生物学重要性的信息。声源定位使动物能够检测到危险并做出适当反应，也使捕食者能够检测并定位猎物。在许多物种中，快速波动的声音也是同种个体之间交流的基础。这些信息并非直接由耳朵的输出提供，而是需要对听神经纤维的音频排列中放电的时间模式进行处理。听神经通过几条平行的上行通路传递信息。在通过腹侧耳蜗核及其非哺乳动物同源物的几条主要上行听觉通路中，明显存在用于传递精确时间的解剖学和电生理学特化，包括杯状突触终末和匹配的轴突传导时间。所有高等脊椎动物共有的一条通路持续比较双耳相位以确定声音在方位角上的位置。另一条通路与哺乳动物的高频听力特别相关，并且被认为利用双耳强度差异来定位高频声音。在快速波动的信号中，将一只耳朵的兴奋与另一只耳朵的抑制相平衡，要求这条通路中这些突触输入的时间对于广泛变化的声音刺激而言是匹配且恒定的。外侧丘系的单耳核，其作用尚不清楚（尽管它们在高等脊椎动物中普遍存在），接收来自多条通路的输入，这些通路精确编码时间，有些是通过杯状末梢。
