While the fruit fly you often swat away in the kitchen might feel insignificant, the tiny-winged creatures have played a massive role in scientific discovery since the early 1900s. Scientists have used the humble insect to investigate everything from genetics to flight. Recently, the fruit fly has taken center stage as we work to understand the complex link between neuroscience, what happens in the brain, and physiology, what the body does. This involves studying how inputs into the body, such as what the eye sees, travel through the brain, eventually leading to movement. To better understand how the physical body of the fruit fly is connected to the signals of the nervous system, researchers from Janelia Research Campus and Columbia University (both in the USA), Tübingen University (Germany), Google Deepmind and University College London (in the UK), have created a computer simulation of the entire fruit fly that can walk and fly through its simulated environment as well as the real thing.
Producing such a complex virtual fly was no small feat. First, the team created an incredibly accurate 3D picture of the body of the fruit fly. To do this, they used a high-tech microscope to capture the fruit fly's body in fine detail to build a virtual puppet of a fruit fly. Next, the team included the fly's muscles and nervous system. Using previous research on the nervous system of the fruit fly, the researchers then created a digital map of how various signals enter the fly's eyes, antennae (which sense smell) and touch sensors, feeding those inputs into a simulation that calculated the muscle forces that would be generated by muscles contracting in response to the input sensory signals. The scientists then compared the movements of this fly simulation with real-world videos of physical fruit flies. Over many iterations, the researchers were able to teach the simulation how to link sensory inputs to the resulting movements, creating a more and more life-like digital fruit fly.
Once the virtual fly was responding to its environment in a realistic way, the researchers turned to the next task – making the simulated insect walk and fly – which required incorporating how the legs and wings interact with the physical world, including the impact of friction and how the wings move through the air, which feels sticky when you're the size of a fruit fly. The researchers then taught their virtual fly to walk, fly and explore, as it would if it were alive, by training the simulated fly with video of an actual fly and having the simulated fly move in the same way, given the same environmental conditions. The researchers also set up a series of reality checks for their simulated fly. To ensure that it walked like a fly, they had their virtual fly walk through a simulated narrow trench without bumping the walls. They then set their virtual fly the task of maintaining a constant height while flying over bumpy terrain. On both tests, the virtual insect passed with flying colors. With these checks complete, the virtual insect proved that it walked like a fly and flew like a fly.
This virtual fly represents a massive achievement in the world of biology. Not only did it require a huge amount of interdisciplinary effort across a diverse team of software engineers, physicists, neuroscientists, physiologists and others but also the virtual fruit fly synthesizes decades of study of one of the most important organisms in research. With this digital animal, researchers now have the potential to run experiments on their computers, using this freely accessible model, which used to require specialized equipment and labs to continue deepening our understanding of how an animal's body is tied to how its brain works. The fruit fly might be small but, when simulated, it promises to be quite mighty.
