Chair of Zoology, School of Life Sciences, Technical University of Munich, Freising-Weihenstephan 85354, Germany.
Chair of Zoology, School of Life Sciences, Technical University of Munich, Freising-Weihenstephan 85354, Germany
J Neurosci. 2022 Jun 8;42(23):4669-4680. doi: 10.1523/JNEUROSCI.2204-21.2022. Epub 2022 May 4.
The optic tectum (OT) is an avian midbrain structure involved in the integration of visual and auditory stimuli. Studies in the barn owl, an auditory specialist, have shown that spatial auditory information is topographically represented in the OT. Little is known about how auditory space is represented in the midbrain of birds with generalist hearing, i.e., most of avian species lacking peripheral adaptations such as facial ruffs or asymmetric ears. Thus, we conducted extracellular recordings of single neurons in the OT and in the external portion of the formatio reticularis lateralis (FRLx), a brain structure located between the inferior colliculus (IC) and the OT, in anaesthetized chickens of either sex. We found that most of the auditory spatial receptive fields (aSRFs) were spatially confined both in azimuth and elevation, divided into two main classes: round aSRFs, mainly present in the OT, and annular aSRFs, with a ring-like shape around the interaural axis, mainly present in the FRLx. Our data further indicate that interaural time difference (ITD) and interaural level difference (ILD) play a role in the formation of both aSRF classes. These results suggest that, unlike mammals and owls which have a congruent representation of visual and auditory space in the OT, generalist birds separate the computation of auditory space in two different midbrain structures. We hypothesize that the FRLx-annular aSRFs define the distance of a sound source from the axis of the lateral visual fovea, whereas the OT-round aSRFs are involved in multimodal integration of the stimulus around the lateral fovea. Previous studies implied that auditory spatial receptive fields (aSRFs) in the midbrain of generalist birds are only confined along azimuth. Interestingly, we found SRFs s in the chicken to be confined along both azimuth and elevation. Moreover, the auditory receptive fields are arranged in a concentric manner around the overlapping interaural and visual axes. These data suggest that in generalist birds, which mainly rely on vision, the auditory system mainly serves to align auditory stimuli with the visual axis, while auditory specialized birds like the barn owl compute sound sources more precisely and integrate sound positions in the multimodal space map of the optic tectum (OT).
视顶盖（OT）是一种参与视觉和听觉刺激整合的鸟类中脑结构。在听觉专家仓鸮中的研究表明，空间听觉信息在 OT 中呈拓扑分布。关于听觉空间如何在具有一般听觉的鸟类的中脑中表示，知之甚少，即大多数缺乏面部羽毛或不对称耳朵等外围适应的鸟类物种。因此，我们在麻醉的雄性和雌性鸡中进行了视顶盖（OT）和外侧网状形成层（FRLx）外部的单个神经元的细胞外记录，FRLx 是位于下丘（IC）和 OT 之间的脑结构。我们发现，大多数听觉空间感受野（aSRF）在方位和仰角上都受到限制，分为两类：主要存在于 OT 中的圆形 aSRF 和以两耳轴为中心的环形 aSRF，主要存在于 FRLx 中。我们的数据进一步表明，两耳时差（ITD）和两耳强度差（ILD）在两种 aSRF 类别的形成中都起作用。这些结果表明，与在 OT 中具有视觉和听觉空间一致表示的哺乳动物和猫头鹰不同，通用鸟类将听觉空间的计算分离到两个不同的中脑结构中。我们假设 FRLx-环形 aSRF 定义了声源与侧视觉中央凹轴的距离，而 OT-圆形 aSRF 参与了 lateral fovea 周围刺激的多模态整合。先前的研究表明，通用鸟类中脑的听觉空间感受野（aSRF）仅沿方位角限制。有趣的是，我们发现鸡中的 SRF 沿方位角和仰角都受到限制。此外，听觉感受野以同心圆的方式围绕重叠的两耳和视觉轴排列。这些数据表明，在主要依赖视觉的通用鸟类中，听觉系统主要用于将听觉刺激与视觉轴对齐，而像仓鸮这样的听觉专门鸟类则更精确地计算声源位置，并在视顶盖（OT）的多模态空间图中整合声音位置。
