Researchers reconstruct the structure of the fruit fly brain for the first time

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The reconstruction of the 50 largest neurons of the connectome in the fly brain.
The reconstruction of the 50 largest neurons of the connectome in the fly brain. Photo: Tyler Sloan and Amy Sterling for FlyWire, Princeton University

An international team of researchers has reconstructed the structure of the brain of a fruit fly (Drosophila melanogaster) for the first time. The scientists from the FlyWire consortium - including biologist Dr. Katharina Eichler from the University of Leipzig - created a so-called connectome, a circuit diagram of the insect’s brain. This is considered a milestone by experts, as it is the largest brain circuit diagram ever created. Accompanying studies demonstrate the usefulness of the connectome for research into neuronal processes and provide an insight into how this resource will revolutionize the field of research. For the first time, nine papers have been published in an issue of the renowned scientific journal "Nature"; Eichler was involved in six of them.

Everything we do, think or feel arises from the patterns of activity in our brain, which depend on the connections of our brain cells. Many neuroscientists believe that understanding brain function is made possible by mapping all the neurons and connections of the brain - the connectome. This is an incredibly complex task, as the human brain contains more than 80 billion neurons and 100 trillion connections. The fruit fly brain, on the other hand, contains a million times fewer neurons than the human brain. Nevertheless, flies can exhibit complex behaviors such as navigation, learning, and social interactions.

In the journal "Nature", researchers Sven Dorkenwald from Princeton University (USA), Dr. Philipp Schlegel from the University of Cambridge (UK) and their colleagues describe the first complete mapping of the connectome of the adult Drosophila brain. Researcher Dr. Katharina Eichler from the Institute of Biology at Leipzig University was part of the international FlyWire consortium. The project was based on electron microscopy images collected in 2018 using new imaging technologies. The FlyWire team developed methods to precisely align the images and used machine vision to automatically reconstruct individual neurons. To correct for errors, the team built a computer-based infrastructure that allowed researchers worldwide to review the neuron reconstructions. This massive undertaking ultimately led to success: a complete Drosophila brain connectome comprising approximately 140,000 neurons and 54.5 million synapses.

"In the accompanying work, as part of the FlyWire team, I have already been able to use this unique resource to track neural circuits, generate hypotheses about their function and create circuit models based on actual connectivity," explains Katharina Eichler. In the long term, this scientific breakthrough could be an essential step towards answering one of the biggest mysteries in neuroscience: How does a brain actually work?

The fly connectome gives us insights into how information is processed in the brain and converted into behavior. Some of these principles are probably organized in a very similar way in the human brain. In addition, many techniques have been developed and research progress made through this project, which are an important step towards the mouse connectome or perhaps in a few years the human connectome," says Dr. Katharina Eichler, giving an outlook.