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

昆虫和脊椎动物是高度机动的生物，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徙，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，海马体-内嗅觉系统在空间定向中起着关键作用。对空间位置(位置单元、网格单元)和方向(头部方向单元)进行编码的神经元构成了内部映射型空间记忆。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，包括天空指南针方向和空间记忆任务。许多昆虫通过蓝天中依赖太阳的偏振模式间接探测太阳的位置。在沙漠蝗虫中，天空极化的方向在中央复合体中以地形表示，这表明它起到了内部天空罗盘的作用。这里提出的工作将进一步分析这种指南针状的排列，并探索潜在的神经网络。偏振光感受野的特征将显示，中央复合体编码的是横跨大脑中线的360°方位(水平)空间表示，还是180°范围内方向的双重表示。此外，还将探索这种极化复制的潜在神经机制。具体地说，将分析原脑桥两个半球之间的反馈电路，这是中央复合体的主要部分，以确定它们在产生和稳定内部罗盘方面的可能作用。这些数据不仅与更好地理解昆虫的空间定向有关，而且与脊椎动物大脑中类似的地形组织相比也具有很高的相关性，例如初级视觉皮质中定向柱的空间排列。

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.