The auditory cortex (AC) modulates the activity of upstream pathways in the auditory brainstem via descending (corticofugal) projections. This feedback system plays an important role in the plasticity of the auditory system by shaping response properties of neurons in many subcortical nuclei. The majority of layer (L) 5 corticofugal neurons project to the inferior colliculus (IC). This corticocollicular (CC) pathway is involved in processing of complex sounds, auditory-related learning, and defense behavior. Partly due to their location in deep cortical layers, CC neuron population activity patterns within neuronal AC ensembles remain poorly understood. We employed two-photon imaging to record the activity of hundreds of L5 neurons in anesthetized as well as awake animals. CC neurons are broader tuned than other L5 pyramidal neurons and display weaker topographic order in core AC subfields. Network activity analyses revealed stronger clusters of CC neurons compared to non-CC neurons, which respond more reliable and integrate information over larger distances. However, results obtained from secondary auditory cortex (A2) differed considerably. Here CC neurons displayed similar or higher topography, depending on the subset of neurons analyzed. Furthermore, specifically in A2, CC activity clusters formed in response to complex sounds were spatially more restricted compared to other L5 neurons. Our findings indicate distinct network mechanism of CC neurons in analyzing sound properties with pronounced subfield differences, demonstrating that the topography of sound-evoked responses within AC is neuron-type dependent.

中文翻译：

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第 5 层听觉皮层内皮质神经元的独特拓扑组织和网络活动模式

听觉皮层 (AC) 通过下行（皮质）投射调节听觉脑干上游通路的活动。这种反馈系统通过塑造许多皮层下核中神经元的反应特性，在听觉系统的可塑性中发挥着重要作用。大多数第 5 层 (L) 皮质神经元投射到下丘 (IC)。该皮质皮质 (CC) 通路参与复杂声音的处理、听觉相关学习和防御行为。部分由于它们位于皮质深层，神经元 AC 群内的 CC 神经元群体活动模式仍然知之甚少。我们采用双光子成像来记录麻醉和清醒动物中数百个 L5 神经元的活动。CC 神经元比其他 L5 锥体神经元具有更广泛的调谐，并且在核心 AC 子域中显示出较弱的拓扑顺序。网络活动分析显示，与非 CC 神经元相比，CC 神经元簇更强，它们的响应更可靠，并能在更远的距离上整合信息。然而，从次级听觉皮层 (A2) 获得的结果差异很大。这里，CC 神经元表现出相似或更高的形貌，具体取决于分析的神经元子集。此外，特别是在 A2 中，与其他 L5 神经元相比，响应复杂声音而形成的 CC 活动簇在空间上受到更多限制。我们的研究结果表明，CC 神经元在分析具有明显子场差异的声音特性时具有独特的网络机制，表明 AC 内声音诱发反应的拓扑结构是神经元类型依赖性的。