Researchers unveil the first complete wiring diagram of the fruit fly brain, offering transformative insights into brain function and behaviour.

In a remarkable scientific achievement, researchers have mapped the complete wiring diagram of the fruit fly’s brain, a breakthrough that promises to reshape our understanding of neuroscience. This ambitious project, known as the FlyWire project, reveals intricate details about the brain’s architecture, showcasing a network of 139,255 neurons and an astounding 50 million connections—all packed into a brain the size of a poppy seed.

Sebastian Seung, a professor of computer science and neuroscience at Princeton University and co-leader of the project, addressed a common question: “Why should we care about the brain of a fruit fly?” His answer is straightforward: understanding how any brain functions will ultimately inform us about all brains. This endeavour is a pivotal step toward deciphering the fundamental workings of neural systems across species.

The intricate network of neurons, which if laid out would stretch approximately 150 meters, was painstakingly assembled over several years. The researchers began by slicing a female fruit fly’s brain into 7,000 ultra-thin sections. These slices were then imaged using electron microscopes, revealing structures as minuscule as four-millionths of a millimetre wide. The sheer volume of data collected was immense, and it called for innovative analytical methods.

To tackle this challenge, the team utilized artificial intelligence (AI) to sift through millions of images and map out each neuron and synaptic connection. However, the initial AI analyses were not without errors. To refine the results, a global network of scientists and volunteers stepped in to correct mistakes and finalize the wiring diagram.

This groundbreaking work is already yielding insights. Utilizing the wiring diagram, researchers have identified “interrogator” neurons that process diverse information and “broadcaster” neurons that send signals to coordinate activity across different neural circuits. They also pinpointed a specific neural circuit responsible for halting fruit flies in their tracks during movement—a fascinating discovery that highlights the practical applications of the research.

Furthermore, researchers constructed a computer simulation of part of the fruit fly brain based on the wiring diagram. Experiments conducted with this simulation led to the identification of neural circuits involved in taste processing, indicating the potential for future simulations to reveal how brain wiring translates into animal behaviour.

“Connectomics is the beginning of a digital transformation of neuroscience,” Seung remarked. “This transformation will extend to brain simulation.” He predicts a rapid acceleration in neuroscience research, paving the way for new methodologies and discoveries.

The collaborative project, which included researchers from Canada, Germany, and the UK’s MRC Laboratory of Molecular Biology and the University of Cambridge, is documented in nine papers published in the journal Nature. Dr. Anita Devineni, a neuroscientist at Emory University, hailed the wiring diagram as a “landmark achievement” in the field.

Following this milestone, efforts are already underway to produce a complete wiring diagram for the mouse brain, with an expected completion timeline of five to ten years. However, replicating this success for the human brain—composed of approximately 86 billion neurons and trillions of connections—poses an entirely different challenge. The human brain is about a million times more complex than that of the fruit fly, making a comprehensive wiring diagram an impractical goal with current technology. Estimates suggest that mapping a human brain’s wiring would generate an astounding amount of data, potentially amounting to a zettabyte—equivalent to all of the world’s internet traffic for an entire year.

Instead of attempting to map the entire human brain, researchers advocate for a more feasible approach: mapping neuronal wiring in specific brain regions. This targeted research could provide critical insights into neuropsychiatric disorders and other brain conditions. Dr. John Ngai, director of the US National Institutes of Health’s Brain Initiative, emphasized the importance of understanding neural wiring: “Simply put, we cannot fix what we do not understand, and this is the basis of why we believe this is such an important moment today.”As the research community embarks on this ambitious journey, it’s clear that understanding the complex web of connections in the brain—starting with the fruit fly—could unlock the secrets of behaviour and brain function across all living beings.