Bajo Victoria M, Nodal Fernando R, Bizley Jennifer K, Moore David R, King Andrew J
Department of Physiology, Anatomy and Genetics, Sherrington Building, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
Cereb Cortex. 2007 Feb;17(2):475-91. doi: 10.1093/cercor/bhj164. Epub 2006 Mar 31.
Descending corticofugal projections are thought to play a critical role in shaping the responses of subcortical neurons. Here, we examine the origins and targets of ferret auditory corticocollicular projections. We show that the ectosylvian gyrus (EG), where the auditory cortex is located, can be subdivided into middle, anterior, and posterior regions according to the pattern of cytochrome oxidase staining and immunoreactivity for the neurofilament antibody SMI32. Injection of retrograde tracers in the inferior colliculus (IC) labeled large layer V pyramidal cells throughout the EG and adjacent sulci. Each region of the EG has a different pattern of descending projections. Neurons in the primary auditory fields in the middle EG project to the lateral nucleus (LN) of the ipsilateral IC and bilaterally to the dorsal cortex and dorsal part of the central nucleus (CN). The projection to these dorsomedial regions of the IC is predominantly ipsilateral and topographically organized. The secondary cortical fields in the posterior EG target the same midbrain areas but exclude the CN of the IC. A smaller projection to the ipsilateral LN also arises from the anterior EG, which is the only region of auditory cortex to target tegmental areas surrounding the IC, including the superior colliculus, periaqueductal gray, intercollicular tegmentum, and cuneiform nucleus. This pattern of corticocollicular connectivity is consistent with regional differences in physiological properties and provides another basis for subdividing ferret auditory cortex into functionally distinct areas.
下行皮质传出投射被认为在塑造皮质下神经元的反应中起关键作用。在这里，我们研究雪貂听觉皮质-丘系投射的起源和靶点。我们发现，听觉皮层所在的外侧沟回（EG）可根据细胞色素氧化酶染色模式和神经丝抗体SMI32的免疫反应性分为中部、前部和后部区域。在下丘（IC）注射逆行示踪剂标记了整个EG和相邻脑沟中的大的V层锥体细胞。EG的每个区域都有不同的下行投射模式。中部EG初级听觉区的神经元投射到同侧IC的外侧核（LN），并双侧投射到背侧皮层和中央核（CN）的背侧部分。向IC这些背内侧区域的投射主要是同侧的且具有拓扑组织。后部EG的次级皮质区靶向相同的中脑区域，但不包括IC的CN。来自前部EG的较小投射也投射到同侧LN，前部EG是听觉皮层中唯一靶向IC周围被盖区域的区域，包括上丘、导水管周围灰质、丘间被盖和楔形核。这种皮质-丘系连接模式与生理特性的区域差异一致，并为将雪貂听觉皮层细分为功能不同的区域提供了另一个基础。
