Department of Animal Physiology, Philipps-University Marburg, 35032 Marburg, Germany.
Center for Mind, Brain and Behavior (CMBB), Philipps-University Marburg and Justus Liebig University Giessen, 35032 Marburg, Germany.
Proc Natl Acad Sci U S A. 2020 Oct 13;117(41):25810-25817. doi: 10.1073/pnas.2005192117. Epub 2020 Sep 28.
Many animals use celestial cues for spatial orientation. These include the sun and, in insects, the polarization pattern of the sky, which depends on the position of the sun. The central complex in the insect brain plays a key role in spatial orientation. In desert locusts, the angle of polarized light in the zenith above the animal and the direction of a simulated sun are represented in a compass-like fashion in the central complex, but how both compasses fit together for a unified representation of external space remained unclear. To address this question, we analyzed the sensitivity of intracellularly recorded central-complex neurons to the angle of polarized light presented from up to 33 positions in the animal's dorsal visual field and injected Neurobiotin tracer for cell identification. Neurons were polarization sensitive in large parts of the virtual sky that in some cells extended to the horizon in all directions. Neurons, moreover, were tuned to spatial patterns of polarization angles that matched the sky polarization pattern of particular sun positions. The horizontal components of these calculated solar positions were topographically encoded in the protocerebral bridge of the central complex covering 360° of space. This whole-sky polarization compass does not support the earlier reported polarization compass based on stimulation from a small spot above the animal but coincides well with the previously demonstrated direct sun compass based on unpolarized light stimulation. Therefore, direct sunlight and whole-sky polarization complement each other for robust head direction coding in the locust central complex.
许多动物利用天体线索进行空间定位。这些线索包括太阳，以及在昆虫中，天空的偏振模式，它取决于太阳的位置。昆虫大脑中的中央复合体在空间定位中起着关键作用。在沙漠蝗中，动物头顶上方的偏振光角度和模拟太阳的方向在中央复合体中以类似罗盘的方式表示，但两个罗盘如何结合在一起以统一表示外部空间仍然不清楚。为了解决这个问题，我们分析了细胞内记录的中央复合体神经元对来自动物背部视觉场多达 33 个位置的偏振光角度的敏感性，并注入 Neurobiotin 示踪剂用于细胞鉴定。在虚拟天空的大部分区域，神经元对偏振光敏感，在某些细胞中，这种敏感性向各个方向延伸到地平线。此外，神经元对与特定太阳位置的天空偏振模式相匹配的偏振角度空间模式进行了调谐。这些计算出的太阳位置的水平分量在中央复合体的protocerebral bridge 中被地形编码，覆盖了 360°的空间。这个全天空偏振罗盘不支持之前基于动物上方小光斑刺激的报道的偏振罗盘，而是与之前基于非偏振光刺激的直接太阳罗盘很好地吻合。因此，直接阳光和全天空偏振相互补充，为蝗中央复合体中的稳健头部方向编码提供了支持。
