Researchers have created the first wiring diagram for the entire brain of a fruit fly, which promises to revolutionize the field of neuroscience and lead to unprecedented insights into how the brain generates behaviors.
Rarely in science has so much effort been devoted to such small objects, and it took scientists years to map the windings of all 139,255 neurons and 50 meters of connections packed into a fly’s poppy-seed-sized brain.
In the process, the researchers characterized more than 8,400 different cell types, amounting to the first complete list of parts that make up a fly brain.
“You might ask why we should look at the brain of the fruit fly,” says co-leader Sebastian Cheung, professor of computer science and neuroscience at Princeton University. FlyWire project. “My simple answer is that if we can really understand how any brain works, it will tell us a lot about all brains.”
Untangling the intricate tangle of neurons, which can reach 150 meters, was mapped through a painstaking process that began by cutting the brain of a female fruit fly into 7,000 thin slices. Each section was imaged in an electron microscope to reveal structures as small as four millionths of a millimeter in width.
The researchers turned to artificial intelligence (AI) to analyze millions of images and trace the path of each neuron and synaptic connection across the tiny organ. Because the AI made so many mistakes, a global army of scientists and volunteers was recruited to help correct the errors and finalize the map.
The work has already paid off. Armed with the map, researchers discovered “interrogator” neurons that integrate different types of information and “broadcasters” that can send signals to coordinate activity in different neural circuits. A specific neural circuit, when stimulated, causes fruit flies to stop in their tracks as they walk.
In a harbinger of what was to come, the researchers used a wiring diagram called a connectome to create a computer simulation of part of a fly brain. Experiments with simulations have led to the identification of neural circuits used to process taste, suggesting that future simulations may shed more light on how brain wiring leads to animal behavior.
“Connectomics is the beginning of the digital transformation of neuroscience … and this transformation will extend to brain simulation,” Cheung said. “This will be the fastest acceleration of neuroscience we can do.”
Details of the project, which involved researchers from Canada, Germany and the MRC Laboratory of Molecular Biology and the University of Cambridge in England, have been published throughout. Nine sheets in nature. In an accompanying article, Dr. Anita Devineni, a neuroscientist at Emory University in Atlanta, called the wiring diagram a “landmark achievement.”
Work has already begun on creating a complete wiring diagram for the mouse brain, which the researchers hope to complete in five to 10 years. But repeating the feat for the entire human brain with its 86 billion neurons and trillions of connections is another question. The human brain is about a million times more complex than a fruit fly brain, putting a complete wiring diagram out of practice with today’s technology. It would require a lot of memory: scientists estimate it would be a zettabyte of data, equivalent to all the world’s internet traffic for a year.
A more realistic approach is to map neural wiring in certain areas of the human brain, which may eventually shed light on whether faulty wiring underlies neuropsychiatric and other brain disorders. “Simply put, we can’t fix what we don’t understand, and that’s the basis of why we believe this is the most important moment today,” said Dr. John Nakai, director of the US National Institutes of Health’s Brain Initiative.
“We have a big task ahead of us.”
