FUNCTIONAL ANATOMY OF THE AUDITORY PATHWAYS

听觉系统由上行通路和下行通路组成，上行通路将信息从耳朵传输到能感知声音的大脑皮层，而大脑皮层下行通路调节上行信息的处理和流动。下行通路在多种功能中发挥作用，包括选择性注意、学习、频率选择性、声音定位和语音辨别。以前关于下行通路的大部分工作都集中在从脑干到耳蜗的投射上。对投射到耳蜗的细胞的形态、生理和递质化学的表征导致了我们对这一橄榄耳蜗系统的理解取得了重大进展。我们对剩下的下行通路的了解远远落后，其中一些涉及的细胞比橄榄耳蜗系统多得多。我们建议使用敏感的新解剖学追踪技术的组合来检查下行听觉通路的一些最大组成部分的功能组织。我们的实验集中在从听觉皮质到脑干听觉核团的投射上。最近的发现突显了这一途径的重要性，这些发现表明，皮质投射比之前认为的要广泛得多，一直延伸到耳蜗核，这是听觉信息进入大脑的地方。我们实验的一个目标是识别由大脑皮层下行投射直接联系的脑干回路。第二个目标是确定产生下行投射的细胞和听觉皮质功能组织之间的解剖关系。研究结果应该能提供对下行投射传递的信息类型的洞察，以及受这些投射影响的脑干回路的识别。这些信息将反过来为解释其他类型的研究结果提供解剖学基础，并最终帮助我们理解下行通路在正常和疾病或受损大脑中的作用。

The auditory system consists of ascending pathways that transmit information from the ear to the cortex, where sound is perceived, and descending pathways from the cortex that modulate the processing and flow of ascending information. The descending pathways play a role in a wide variety of functions, including selective attention, learning, frequency selectivity, sound localization, and discrimination of speech sounds. Much of the previous work on descending pathways has focused on projections from the brainstem to the cochlea. Characterization of the morphology, physiology and transmitter chemistry of the cells that project to the cochlea has led to major advances in our understanding of this olivocochlear system. Our understanding of the remaining descending pathways, some of which involve many more cells than the olivocochlear system, lags far behind. We propose to use combinations of sensitive new anatomical tracing techniques to examine the functional organization of some of the largest components of the descending auditory pathways. Our experiments are focused on the projections from the auditory cortex to the brainstem auditory nuclei. The importance of this pathway was highlighted by recent discoveries that the cortical projections are far more extensive than previously believed, extending as far as the cochlear nucleus, which is the site of entry of auditory information into the brain. One goal of our experiments is to identify the brainstem circuits that are contacted directly by descending projections from the cortex. A second goal is to identify the anatomical relationships between the cells that give rise to the descending projections and the functional organization of auditory cortex. The results should provide insights into the types of information being transmitted by the descending projections as well as the identity of the brainstem circuits that are affected by these projections. This information will provide in turn an anatomical basis for interpreting the results from other types of studies and, eventually, help us understand the role of the descending pathways in both the normal and the diseased or damaged brain.