The effect of feedback connections on information processing at the first visual synapse of Drosophila and on the animal behaviour

大脑决定我们注视的位置、内容和方式。从哺乳动物到昆虫，我们知道从大脑中心到感觉细胞以及感觉器官本身都有重要的反馈。然而，我们对这些神经元如何参与感官信息的处理知之甚少。虽然人类可以将目光集中在感兴趣的物体上，但昆虫却不能这样做，因为它们复眼的晶状体具有固定的焦距。相反，他们的注意力控制可能是在第一视觉突触的水平上以协调信号的形式发生的，第一视觉突触是感光神经元支配大脑的部位。在许多动物中，第一个视觉突触利用连续的电子信息而不是电子脉冲来传递信息，因为这提供了更丰富的交流。在果蝇的光感受器-LMC（大单极细胞;第一个视觉神经元）突触中也是如此，其中六个相同的光感受器看到同一个小视野连接到一个LMC，以提高其联合传输的质量。然而，这是对发生在第一视觉突触的信息处理的过度简化的看法。就像脊椎动物的眼睛一样，光感受器与大脑之间的交流并不是单向的，相反，与光感受器突触相连的细胞也会将信息反馈给光感受器。然而，这种反馈通信的重要性却知之甚少，部分原因是监测小视觉神经元之间的电子信息非常困难。在这里，我们建议研究（i）光感受器和外周神经元之间的通信和（ii）光感受器和更多的中央视觉神经元之间的通信使苍蝇能够在空间和时间上从视觉场景中提取和过滤信息，并将这些信息传递到更高的视觉中心和大脑。这一战略是促进（1）基因工程果蝇的可能性（2）其视觉系统的有利位置和结构，（3）我们从视觉神经元进行高质量电记录的能力，以及（4）行为测试，在那里我们比较了野生型果蝇和突变型果蝇的学习性能，这些突变型果蝇具有反馈到光感受器的通信通道故障。

The brain selects where, what and how we gaze. From mammals to insects we know that there are important feedbacks from the brain centres to the sense cells, and within the sense organs themselves. However, we know little how these contribute to the processing of sensory information. Whereas humans can focus their gaze on objects of interest, insects cannot do so, as the lenses of their compound eyes have fixed focal ranges. Instead, it is likely that their attention control may take place in a form of coordinated signalling at the level of the first visual synapses, the sites where the photoreceptor neurons innervate the brain. In many animals the first visual synapses utilise continuous electrical messages instead of electrical impulses to transmit information as this provides richer communication. This is also so in the photoreceptor-LMC (large monopolar cell; the first visual interneurone) synapse in fly, where six identical photoreceptors that look at the same small visual field connect to one LMC to improve the quality of their joint transmission. Yet, this is an overly simplified view of the information processing taking place at the first visual synapse. As in the vertebrate eye, the communication from photoreceptors to the brain occurs not just one way, but instead the cells that are synaptically linked to photoreceptors feed also information back to photoreceptors. The significance of this feedback communication is, however, poorly understood, in part because monitoring in electrical messages between small visual neurones is very difficult. Here, we propose to study how the communication between (i) photoreceptors and peripheral neurones and between (ii) photoreceptors and more central visual neurones of the fly enables it to extract and filter information from the visual scene in space and in time, and relay this information to higher visual centres and to the brain. This strategy is facilitated by (1) the possibility of genetically engineering fruit flies (Drosophila melanogaster) whose neurones display reduced or increased activity, (2) the favourable location and architecture of their visual systems, (3) our ability to perform high quality electrical recordings from visual neurones and (4) the behavioural tests, where we compare the learning performance of wild-type flies and mutant variants that have malfunctioning communication channels feeding back to photoreceptors.