A directional tuning map of Drosophila elementary motion detectors
A directional tuning map of Drosophila elementary motion detectors
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DOI：
10.1038/nature12320
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发表时间：
2013-08-08
期刊：
影响因子：
64.8
通讯作者：
Borst, Alexander
中科院分区：
文献类型：
--
作者：
Maisak, Matthew S.;Haag, Juergen;Borst, Alexander
从不断变化的视网膜图像中提取方向运动信息是任何视觉系统中最早且最重要的处理步骤之一。在果蝇的视叶中，从解剖学上已经描述了两条平行的处理流，它们从两个一级中间神经元L1和L2出发，经过T4和T5细胞，到达小叶板的大型、宽视野的运动敏感中间神经元。因此，T4和T5细胞被认为在运动处理中具有关键作用；然而，由于它们体积小，很难获得T4和T5细胞的电生理记录，这使得它们的视觉反应特性在很大程度上不为人知。我们通过使用基因编码的钙指示剂GCaMP5（参考文献2）对果蝇的这些细胞进行光学记录来规避这个问题。在此我们发现，T4和T5细胞的特定亚群对四个基本方向之一具有方向选择性，即从前到后、从后到前、向上和向下。根据它们偏好的方向，T4和T5细胞终止于小叶板的特定亚层。T4和T5在对比度极性方面具有功能上的分离：T4细胞选择性地对移动的亮度增加（亮边）作出反应，而T5细胞仅对移动的亮度减少（暗边）作出反应。当T4或T5细胞的输出被阻断时，突触后的小叶板神经元对移动的亮边（T4阻断）或暗边（T5阻断）的反应会有选择性地受损。在系绳行走的果蝇的转向反应中也能看到相同的效果。因此，从L1和L2开始，视觉输入被分为独立的亮边和暗边通路，并且在每个通路内分别计算沿所有四个基本方向的运动。然后对这八种不同的运动探测器的输出进行分类，使得具有相同方向选择性的亮边（T4）和暗边（T5）运动探测器在小叶板的同一层汇聚，共同为下游电路和运动驱动的行为提供输入。
The extraction of directional motion information from changing retinal images is one of the earliest and most important processing steps in any visual system. In the fly optic lobe, two parallel processing streams have been anatomically described, leading from two first-order interneurons, L1 and L2, via T4 and T5 cells onto large, wide-field motion-sensitive interneurons of the lobula plate(1). Therefore, T4 and T5 cells are thought to have a pivotal role in motion processing; however, owing to their small size, it is difficult to obtain electrical recordings of T4 and T5 cells, leaving their visual response properties largely unknown. We circumvent this problem by means of optical recording from these cells in Drosophila, using the genetically encoded calcium indicator GCaMP5 (ref. 2). Here we find that specific subpopulations of T4 and T5 cells are directionally tuned to one of the four cardinal directions; that is, front-to-back, back-to-front, upwards and downwards. Depending on their preferred direction, T4 and T5 cells terminate in specific sublayers of the lobula plate. T4 and T5 functionally segregate with respect to contrast polarity: whereas T4 cells selectively respond to moving brightness increments (ON edges), T5 cells only respond to moving brightness decrements (OFF edges). When the output from T4 or T5 cells is blocked, the responses of postsynaptic lobula plate neurons to moving ON (T4 block) or OFF edges (T5 block) are selectively compromised. The same effects are seen in turning responses of tethered walking flies. Thus, starting with L1 and L2, the visual input is split into separate ON and OFF pathways, and motion along all four cardinal directions is computed separately within each pathway. The output of these eight different motion detectors is then sorted such that ON (T4) and OFF (T5) motion detectors with the same directional tuning converge in the same layer of the lobula plate, jointly providing the input to downstream circuits and motion-driven behaviours.