Researchers, supported by the NIH’s BRAIN Initiative, have created a comprehensive map of the fruit fly brain, identifying all neuron types and synaptic connections.
This detailed connectome facilitates new studies on brain functions such as motor control and decision-making, paving the way for future simulations and insights into complex brain activities.
Groundbreaking Neurobiological Research
A team of scientists supported by the National Institutes of Health (NIH)’s The BRAIN Initiative®, including Davi Bock, Ph.D., Associate Professor of Neurological Sciences at the University of Vermont’s Robert Larner, M.D. College of Medicine, recently made a substantial advancement in neurobiological research by successfully mapping the entire brain of Drosophila melanogaster, commonly known as the fruit fly.
Recently published in the journal Nature, the study, titled “Whole-brain annotation and multi-connectome cell typing of Drosophila,” established a “consensus cell type atlas,” or a comprehensive guide, for understanding the different types of cells in the fruit fly brain. The fruit fly’s brain contains around 130,000 neurons (a human’s brain contains 86 billion; mice, which often stand-in for humans in scientific research and testing, have 100 million neurons).
The electron microscopy dataset underlying the whole-brain connectome (known as FAFB, or “Full Adult Fly Brain”) uses the detailed shapes of every neuron in the fly’s brain as well as all the synaptic connections between them to identify and catalog all cell types in the brain. This complete map will help researchers to identify how different circuits work together to control behaviors like motor control, courtship, decision-making, memory, learning, and navigation.
“If we want to understand how the brain works, we need a mechanistic understanding of how all the neurons fit together and let you think,” remarked study co-lead Gregory Jefferis, Ph.D. “For most brains, we have no idea how these networks function. Now for the fly we have this complete wiring diagram, a key step in understanding complex brain functions. In fact, using our data, shared online as we worked, other scientists have already started trying to simulate how the fly brain responds to the outside world.”
“To begin to simulate the brain digitally, we need to know not only the structure of the brain, but also how the neurons function to turn each other on and off,” remarked study co-lead Gregory Jefferis, Ph.D. “Using our data, which has been shared online as we worked, other scientists have already started trying to simulate how the fly brain responds to the outside world. This is an important start, but we will need to collect many different kinds of data to produce reliable simulations of how a brain functions.”
Significance and Implications of the Fruit Fly Connectome
While similar studies have been done with simpler organisms, such as the nematode worm C. elegans and the larval stage of the fruit fly, the adult fruit fly offers more intricate behaviors to study. Though the fruit fly’s brain is clearly less complex than that of a human, or even a mouse, the implications of the study are profound. There are tremendous commonalities in how neural circuits in all species process information; this work allows principles of information processing to be identified in a simpler model organism and then sought in larger brains. Bock notes that scientists are currently incapable of scaling up this approach to a human brain, but states that this achievement represents a noteworthy step toward complete connectome of a mouse brain.
“This type of work [being done across this field of connectomics] advances the state of the art in a once-in-a-century fashion, allowing us to both map the shapes and connections of every individual neuron in the complete brain of a fairly sophisticated animal, the adult fruit fly, and to annotate and mine the resulting connectome with cutting-edge software analytics. Neither light microscopy—even with multi-color fluorescence—nor the classical Golgi method and its allied approaches has provided this capability,” said Bock. “To achieve this feat at the scale of the entire brain of an important genetic model organism such as the fruit fly represents a remarkable advancement in the field.”
FlyWire Consortium and Collaborative Data Sharing
This study leverages tools and data generated by the FlyWire Consortium, which includes study leads such as UVM’s Bock; Gregory Jefferis, Ph.D., and Philipp Schlegel, Ph.D., from the MRC Laboratory of Molecular Biology and University of Cambridge; and Sebastian Seung, Ph.D. and Mala Murthy, Ph.D., of Princeton University. The consortium used electron microscopic brain images generated previously in Bock’s lab to create a detailed map of connections between neurons in the entire adult brain of a female fruit fly. This map includes around 50 million chemical synapses between the fly’s aforementioned 139,255 neurons.
Researchers also added information about different types of cells, nerves, developmental lineages, and predictions about the neurotransmitters used by neurons. FlyWire’s Connectome Data Explorer open-access data analysis tool is accessible and available for download, and can be browsed interactively—all done in the spirit of encouraging team science. This work is detailed in an accompanying Nature paper, “Neuronal wiring diagram of an adult brain.”
“We have made the entire database open and freely available to all researchers. We hope this will be transformative for neuroscientists trying to better understand how a healthy brain works,” stated Murthy. “In the future we hope that it will be possible to compare what happens when things go wrong in our brains, for example in mental health conditions.”
Conclusion: The Role of the Fruit Fly in Neuroscience
By tracing connections from sensory cells to motor neurons, researchers can uncover potential circuit mechanisms that control behaviors in fruit flies, marking a crucial step toward understanding the complexities of human cognition and behavior.
“The diminutive fruit fly is surprisingly sophisticated and has long served as a powerful model for understanding the biological underpinnings of behavior,” said John Ngai, Ph.D., director of the study’s funding party, NIH’s The BRAIN Initiative®. “This milestone not only provides researchers a new set of tools for understanding how the circuits in the brain drive behavior, but importantly serves as a forerunner to ongoing BRAIN-funded efforts to map the connections of larger mammalian and human brains.”
For more on this breakthrough:
- A Stunning Journey Through 139,255 Neurons Inside the Fruit Fly’s Brain
- Entire Fruit Fly Brain Mapped in Stunning Detail for the First Time
- Complete Neural Blueprint: Scientists Map Over 50 Million Connections in Fruit Fly Brain
References:
“Neuronal wiring diagram of an adult brain” by Sven Dorkenwald, Arie Matsliah, Amy R. Sterling, Philipp Schlegel, Szi-chieh Yu, Claire E. McKellar, Albert Lin, Marta Costa, Katharina Eichler, Yijie Yin, Will Silversmith, Casey Schneider-Mizell, Chris S. Jordan, Derrick Brittain, Akhilesh Halageri, Kai Kuehner, Oluwaseun Ogedengbe, Ryan Morey, Jay Gager, Krzysztof Kruk, Eric Perlman, Runzhe Yang, David Deutsch, Doug Bland, Marissa Sorek, Ran Lu, Thomas Macrina, Kisuk Lee, J. Alexander Bae, Shang Mu, Barak Nehoran, Eric Mitchell, Sergiy Popovych, Jingpeng Wu, Zhen Jia, Manuel A. Castro, Nico Kemnitz, Dodam Ih, Alexander Shakeel Bates, Nils Eckstein, Jan Funke, Forrest Collman, Davi D. Bock, Gregory S. X. E. Jefferis, H. Sebastian Seung, Mala Murthy and The FlyWire Consortium, 2 October 2024, Nature.
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“Connectomic reconstruction predicts visual features used for navigation” by Dustin Garner, Emil Kind, Jennifer Yuet Ha Lai, Aljoscha Nern, Arthur Zhao, Lucy Houghton, Gizem Sancer, Tanya Wolff, Gerald M. Rubin, Mathias F. Wernet and Sung Soo Kim, 2 October 2024, Nature.
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