The first wiring diagram of each neuron in an adult brain and the 50 million connections between them has been produced for a fruit fly. This historic achievement has been carried out by a large international group of scientists, called FlyWire Consortiumwhich includes researchers from Molecular Biology Laboratory of the MRC and the University of Cambridge (United Kingdom)Princeton University and the University of Vermont (both in the United States). It is published in a couple of articles in Nature.
The diagram of the 139,255 neurons in the brain of an adult fly is the first of a complete brain of an animal that can walk and see. In previous studies they have made complete brain diagrams much smaller, such as that of a fruit fly larva, which has 3,016 neurons, and that of a nematode worm, which has 302 neurons.
The researchers say mapping the fly’s complete brain is a key first step toward completing larger brains. Since the fruit fly is a common tool in research, its brain map can be used to advance our understanding of how neural circuits work.
Dr. Gregory Jefferisof the Molecular Biology Laboratory of the MRC and the University of Cambridgewho was one of the co-leaders of the research, comments: “If we want to understand how the brain works, we need a mechanistic understanding of how all the neurons fit together and allow you to think. “For most brains, we have no idea how these networks work.”
«Flies can do all kinds of complicated things, like walking, flying, finding your way, and males sing to females. Brain wiring diagrams are a first step to understanding everything that interests us: how we control our movement, answer the phone or recognize a friend,” he warned.
For its part, Dr. Mala Murthyfrom Princeton University, one of the co-leaders of the research, adds “We have made the entire database available to all researchers free and openly. We hope this is transformative for neuroscientists who are trying to better understand how a healthy brain works. “In the future we hope it will be possible to compare what happens when things go wrong in our brain, for example in mental health disorders.”
The scientists discovered that there were substantial similarities between the wiring of this map and previous smaller-scale work that had been done. mapped parts of the fly’s brain. This led researchers to conclude that there are many similarities in wiring between individual brains, that each brain is not a unique structure like a snowflake.
By comparing your brain diagram with previous diagrams of small areas of the brain, lThe researchers also found that about 0.5% of neurons present developmental variations that could cause the connections between neurons to be poorly connected. The researchers say this will be an important area for future research to understand whether these changes are related to individuality or brain disorders.
The brain of an entire fly is less than a millimeter wide. The researchers started with a female brain cut into seven thousand slices, each just 40 nanometers thick, which were pre-scanned with high-resolution electron microscopy in the laboratory of the project’s co-director, David Bockthen at the Janelia Research Campus in the United States.
Analyze more than 100 terabytes of image data (equivalent to the storage of 100 typical laptop computers) to extract the shapes of approximately 140,000 neurons and 50 million connections among them is too challenging for humans to complete manually. Therefore, the researchers relied on artificial intelligence developed at Princeton University to identify and map neurons and their connections to each other.
However, AI still makes many mistakes on data sets of this size. The FlyWire Consortium, made up of teams from more than 76 laboratories and 287 researchers around the world, as well as volunteers from the general public, spent approximately 33 person-years thoroughly reviewing all the data.
Dr. Sebastian Seung, from Princeton University, one of the leaders of the research, reveals: «Whole-brain mapping has been made possible by advances in AI computing; It would not have been possible to reconstruct the entire wiring diagram manually. This is an example of how AI can advance neuroscience. “The fly brain is a milestone on our path toward reconstructing a wiring diagram of the entire mouse brain.”
