Neural basis of the polarization compass in the central complex of the locust brain

昆虫和脊椎动物是高度移动的生物体，因此在空间定位和导航方面表现出复杂的性能。这些包括定向的长距离季节性迁移、地标和太阳罗盘定向以及各种形式的空间学习。在哺乳动物中，外鞘-内嗅系统在空间定向中起着关键作用。编码空间位置（位置细胞，网格细胞）和方向（头部方向细胞）的神经元有助于内部地图型空间记忆。在昆虫中，越来越多的证据表明，中央复合体是控制行为空间方面的大脑区域，包括天空罗盘定向和空间记忆任务。许多昆虫通过蓝天中依赖于太阳的偏振模式间接地探测太阳的位置。在沙漠蝗虫中，天空偏振的方向在中央复合体中表现为地形，这表明它充当了内部天空指南针。本文提出的工作将进一步分析这种类似指南针的排列，并探索底层的神经网络。偏振光感受野的表征将显示中央复合体编码是否为横跨大脑中线的方位角（水平）空间的360°表示或在180°范围内的方向的双重表示。此外，这polarotopy的潜在神经机制将被探索。具体来说，反馈回路之间的两个半球的前脑桥，中央复合体的主要部分，将分析其可能的作用，在产生和稳定的内部指南针。这些数据不仅与更好地理解昆虫的空间定向高度相关，而且与脊椎动物大脑中类似的地形组织（如初级视觉皮层中定向列的空间排列）进行了比较。

Insects and vertebrates are highly mobile organisms and, accordingly, show sophisticated performance in spatial orientation and navigation. These include oriented long-range seasonal migrations, landmark and sun compass orientation, and various forms of spatial learning. In mammals the hippocampal-entorhinal system plays a key role in spatial orientation. Neurons coding for spatial locations (place cells, grid cells) and directions (head-direction cells) contribute to internal map-type spatial memories. In insects, accumulating evidence points to the central complex as the brain area controlling spatial aspects of behaviour, including sky compass orientation and spatial memory tasks. Many insects detect the position of the sun indirectly by the sun-dependent polarization pattern in the blue sky. In desert locusts the orientation of sky polarization is represented topographically in the central complex suggesting that it acts as an internal sky compass. Work proposed here will further analyse this compass-like arrangement and explore the underlying neural network. Characterization of receptive fields for polarized light will show whether the central complex codes for a 360° representation of azimuthal (horizontal) space across the brain midline or a double representation of directions over a range of 180°. Furthermore, the underlying neural mechanisms of this polarotopy will be explored. Specifically, feedback circuits between both hemispheres of the protocerebral bridge, a major part of the central complex, will be analyzed for their possible role in generating and stabilizing the internal compass. The data are highly relevant not only for a better understanding of spatial orientation in insects, but also in comparison to similar topographic organizations in vertebrate brains, like the spatial arrangement of orientation columns in primary visual cortex.