Sky compass signaling of central-complex neurons in locusts exposed to the natural sky

许多昆虫，像脊椎动物一样，可以利用天体线索来编码指南针的方向。对蜜蜂、沙漠蚂蚁、甲虫和帝王蝶的研究表明，太阳的位置、天空的光谱梯度和蓝天的偏振模式可以作为指南针的线索。对偏振敏感神经元的分析，特别是在沙漠蝗虫中，但也在甲虫、帝王蝶和田野蟋蟀中，表明大脑中的中央复合体在天空罗盘方向中起着关键作用。遗憾的是，复杂的天空偏振模式以及天空的色度和强度梯度在实验室中无法真实地模拟。因此，我们将在开阔的天空下研究中枢复合体的极化敏感神经元的活动。为了实现这一目标，我们将通过植入沙漠蝗虫大脑中的电极线进行细胞外记录。首先，在实验室中，当动物在天顶和模拟太阳的背侧光源提供的固定偏振光下旋转时，将监测神经元的活动。然后，这只动物将被转移到研究所屋顶的一个观察平台上。在自然天空下，当动物绕其垂直轴旋转时，将再次研究同一神经元的活动。各种各样的操作，如在眼睛的部分上作画，用扩散器覆盖眼睛或研究日落前后的神经活动，将解决天空的哪些参数和眼睛的哪些区域有助于神经罗盘编码的问题。最后，将讨论地标对中心复合体方向编码的贡献。这项研究是首次在任何动物的自然条件下调查天空罗盘神经元，并将使我们能够批判性地评估在实验室环境中获得的数据的有效性。

Many insects, like vertebrates, can exploit celestial cues for the coding of compass orientation. Studies in honeybees, desert ants, beetles, and monarch butterflies showed that the position of the sun, the spectral gradient across the sky, and the polarization pattern of the blue sky can serve as compass cues. Analysis of polarization-sensitive neurons, especially in the desert locust, but also in beetles, the monarch butterfly, and the field cricket, showed that the central complex in the brain plays a key role in sky compass orientation. Unfortunately, the complex pattern of sky polarization, as well as the chromatic and intensity gradient in the sky cannot be mimicked faithfully in the laboratory. Therefore, we will study the activity of polarization-sensitive neurons of the central complex under the open sky. Toward this goal we will perform extracellular recordings via wire electrodes implanted in the brain of desert locusts. Activity of a neuron will be monitored first in the laboratory during rotation of the animal below stationary polarized light provided from the zenith and a dorso-lateral light source mimicking the sun. The animal will then be transferred to an observation platform on the rooftop of the institute. Under the natural sky the activity of the same neuron will be studied again during rotation of the animal around its vertical axis. Various manipulations such as painting over parts of the eyes, covering the eyes with a diffuser or studying neural activity before and after sunset will address the question of which parameters of the sky and which eye regions contribute to neural compass coding. Finally, the contribution of landmarks to direction coding in the central complex will be addressed. The study is the first to investigate sky compass neurons under natural conditions in any animal and will allow us to critically evaluate the validity of data obtained in laboratory settings.