How does the brain know where to go out of the subway station? Fruit fly neurons or reveal the answer.

Click on the blue word above to pay attention to us! Original author: Malcolm g. Campbell & amp; Lisa M. giocomo two fruit fly studies have revealed how the brain's targeting system links environmental landmarks with self positioning information, which is crucial for accurate navigation.we all know that the sense of direction is important to explore the world.in mammals, this "sense of direction" comes mainly from neurons called "head oriented cells".with landmarks in the environment as the reference system, cells in these directions will become more active one by one when animals face in specific directions.the activity of these cells can indicate the direction that animals face whenever and wherever.in 2015, researchers found that fruit flies also have very similar cells called "directional neurons" 1, which are much better studied than mammals.based on this discovery, Fisher et al. 2 and Kim et al. 3 respectively published articles in nature, trying to answer a question that has existed for decades: how can such neurons balance stability and flexibility, make reliable response to landmark location and quickly adapt to new environment? Source: pixabay, for example, imagine you walk from a subway station to a crowded street. If you take this road often, you will know the direction by looking left and right. But if you come to this subway station for the first time, it takes some time to judge the direction. You may have to look at the signs, shops and landmarks around you.but it won't be long before you know which direction you're going.the above example lists two major challenges that brain targeting systems need to address.first, it must be able to reliably point out the direction in a familiar environment: it can wake up the same positioning every time it returns to the same station; second, it must be flexible enough to quickly master the distribution of new landmarks, even if some of them have been seen before.the neural mechanism behind the positioning ability of Drosophila perfectly explains what form following is.the directional neurons (also known as e-pg or compass neurons) in Drosophila are arranged in a circular pattern (Fig. 1), corresponding to the 360 ° circumferential direction 1 that the Drosophila may face - sometimes also called directional angle.neurons inhibit each other, indicating only one direction angle at a time, providing a clear signal for Drosophila.it should be noted that when the Drosophila enters a new environment, the activity of neurons in these directions is no longer adjusted in a specific direction (e.g. in the North), but is randomly readjusted.directional neurons receive input from neurons in the visual loop, and the activation of neurons in the visual loop mainly depends on visual cues in specific directions and intrinsic cues related to self movement.Fig. 1. Neurons in the central complex of Drosophila brain labeled with fluorescent protein.the central complex of Drosophila consists of a ring-shaped structure called the ellipsoid, in which there are directional neurons.these neurons correspond to all directions that the Drosophila may face, providing signals similar to a compass for the Drosophila to navigate.two studies 2,3 revealed how flies self orient in familiar environments and how they quickly adapt to new environments - thanks to signals from visual loop neurons to directional neurons, which are mainly from the eye (not shown).| source: Tanya Wolff Fisher et al. Tested whether and how the connections between visual loop neurons and directional neurons vary with experience using a number of experimental techniques, many of which can only be achieved in Drosophila.they built a virtual reality (VR) system to let fruit flies crawl on floating balls.a row of lights will flash with the movement of fruit flies, providing visual clues for the flies and helping them locate themselves.as Drosophila explored the virtual environment, the researchers measured the inputs from visual loop neurons to directional neurons.they also suppressed the activity of neurons in the visual circuit through genetic techniques.experiments showed that the visual loop neurons activated by visual cues at a specific angle inhibited the single directional neurons of Drosophila.because of the specificity of the inhibition relationship, visual input enhanced the directional preference of directional neurons.this solves the first problem of subway scene: how the brain stably converts visual input into directional signal in a familiar environment.Fisher and others continue to explore the second question: how directional neurons adapt to the new environment.they gave two identical visual cues to the flies, but the direction was different by 180 degrees - it was a fuzzy environment in which the same visual cues could be seen in half a circle or a circle.because the directional neurons of Drosophila can only indicate one direction angle at a time, these directional neurons need to constantly switch between two completely opposite directions.after the Drosophila was put back into the previous single line world, the relationship between the visual input and the overall activity of the directional network sometimes changed 180 degrees.the intensity of visual input to directional neurons also changes, but it is limited to the directional neurons activated in the environment of double cord.this result indicates that the visual loop neurons and directional neurons form new connections in the new environment. in order to establish new connections, it is not enough to change the visual cues only. It also requires that the neurons in the upstream visual circuit and the directional neurons in the downstream are activated cooperatively, which will weaken the inhibitory synaptic connection between the two, resulting in the decrease of the sensitivity of the directional neurons to the inhibition of the neurons in the visual circuit. This phenomenon is also known as "associative plasticity" plasticity）。 in the complementary experiment carried out by Kim et al., fruit flies were put into the VR scene presented by natural pictures, which was closer to the real world. they stimulated directional neurons in the random direction of visual cues received by Drosophila, and changed the orientation preference of neurons. after stimulation, the shift between the activity of directional neurons and visual input remained unchanged, indicating that the orientation system can establish a new visual direction Association. when combined with stimulation, the local scene can also cause the overall change of the directional neural network. this function of the directional neural network may explain why we can judge the direction without having to look at it all at a new subway station. however, this flexibility has a drawback - if synaptic connections can be changed, will they be eliminated? Kim et al. Wanted to know whether directional networks can "remember" multiple scenarios. first of all, they found that putting fruit flies in different scenes could induce different directional preferences of directional neurons. although this preference varies from individual to individual, it is important that even if a series of different scenes are presented to the Drosophila quickly, each Drosophila's orientation preference for a particular scene is always stable. that is to say, the directional network of Drosophila can store and extract scene memory. at the end of the paper, researchers put forward hypothesis theory to predict which types of scenes can be stored synchronously and how to learn new scenes without deleting the original memory. these two studies are well-designed, which proves that the directional network of Drosophila can learn through associative plasticity. the following work should further explore the memory capacity of this directional system. a key question is whether insects such as fruit flies rely on memory of complex scenes or clues from celestial bodies such as the sun. other types of sensory input may also play a role in determining the direction of insects, such as polarized light and other factors. in addition, molecular and cytological studies are needed to further reveal the mechanism of synaptic plasticity in orientation system, and to verify whether it conforms to the theoretical prediction of Kim team. finally, the hypothesis proposed in this study should be tested in other species, after all, the directional neurons of Drosophila have many similar characteristics to those of mammalian head cells. although fruit flies can never be the protagonist of "subway station scenes", they have deepened our understanding of the neural mechanism behind "sense of direction". more research is waiting for us. < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / References: 1. Seelig, J.D. & amp; jayaraman, V. nature 576, 126 – 131 (2015) (2015), 2. Fisher, y, y, J., Lu, J., D'Alessandro, I. & amp; < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < br / < Strauss, R., Schuster, S. & amp; G ü TZ, K G. J. exp. Biol. 200, 1281 – 1296 (1997). 5. Wehner, R. Annu. Rev. Entomol. 29, 277 – 298 (1984)| doi:10.1038/d41586-019-03443-1