This is the brain of an adult fly: they create the first map of all the neurons

A international collaborationthe Flywire Consortium, has completed the first wiring diagram of each neuron in an adult brain and the 50 million connections between them for a fruit fly.

The diagram of the 139,255 neurons in an adult fly’s brain is the first of a complete brain for an animal that can walk and see. Previous efforts have completed whole-brain diagrams for much smaller brains, for example, that of a fruit fly larva, which has 3,016 neurons, and a nematode worm, which has 302 neurons.

The researchers, publishing their achievement in Nature, say the complete map of the fly brain is a key first step in 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 Jefferis, from the MRC Laboratory of Molecular Biology and the University of Cambridge, who was one of the co-leaders of the research, said in a statement: “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 walk, fly, navigate, and the males sing to the 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.”

The scientists found that there were substantial similarities between the wiring of this map and previous smaller-scale efforts that have mapped parts of the fly 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 their brain diagram with previous diagrams of small areas of the brain, the researchers also discovered that about 0.5% of neurons have developmental variations that could cause 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 entire brain of a fly measures less than 1 millimeter across. The researchers started with a female brain cut into seven thousand slices, each just 40 nanometers thick, which were pre-scanned using high-resolution electron microscopy in the laboratory of project co-director Davi Bock, then at the Research Campus. Janelia in the US

Analyzing more than 100 terabytes of image data (equivalent to the storage on 100 typical laptop computers) to extract the shapes of approximately 140,000 neurons and 50 million connections between them is too challenging for humans to complete manually. The researchers relied on AI 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 in 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 of Princeton University, one of the co-leaders of the research, said: “Advances in AI computing have made whole-brain mapping possible; it would not have been possible to reconstruct the entire wiring diagram manually. This is an example of how artificial intelligence can advance neuroscience. “The fly brain is a milestone on our path toward reconstructing a wiring diagram of the entire mouse brain.”

The researchers also noted many details on the wiring diagram, such as the classification of more than 8,000 cell types throughout the brain. This also allows researchers to select particular systems within the brain for deeper study, such as neurons involved in vision or movement.