In the science fiction film The Fly, a scientist accidentally transforms into a winged insect that ultimately destroys him. In a collection of science articles about the fly, a team of scientists this week unpacked the details of how the Drosophila melanogaster brain operates — paving the way for a better understanding of how the human mind turns senses into actions, processes thoughts, and, perhaps most mysterious of all, stores experiences as memories.
The foundation of the publications in Nature — a culmination of over 10 years of work by a massive international group of researchers — includes two key components: a “parts list” that names and describes the functions of thousands of nerve cells and a “wiring diagram” that maps how these parts are connected.
Seven additional papers explore the implications of how this data can be applied to learn more about how the fly brain works. Taken together, the studies offer the first complete, detailed look at a complex brain.
Mysterious Signals From a Fly’s Brain
The essential question the neuroscientists attacked in this project is how thousands of neurons in the fly brain (and, eventually, billions of neurons in the human brain) work together to process signals that turn into actions. “That’s just a basic mystery,” says Davi Bock, a neuroscience professor at the University of Vermont.
Because the study went beyond just counting and identifying the neurons by type, this becomes a possibility. The map also includes millions of synaptic connections. “With the synaptic connections between the neurons, we can incorporate connectivity into our definition of type,” says Bock. “And that turns out to be very powerful.” How memories are stored and retrieved is perhaps neuroscience’s biggest Black Box. This detailed map may well shed some light on this mystery.
“Your brain is made of 100 billion neurons,” says Bock, one of the study’s lead authors. “By understanding an animal with around 100,000, we can come that much closer to understanding ourselves.”
How Fly Brains Help Us Understand Human Brains
While “scaling up” from fly to human seems like a quantum leap, the data the scientists created should provide a solid launchpad. For example, many of the thousands of neuron types both humans and fruit flies share are similar. As a result of this work, there are now more known named cell types with an identified function in Drosophila than there are in humans. Comparing unknown neurons in the human brain to known ones in fruit flies should help close that gap.
The same goes for how nerves—and basic neural networks—react to basic stimuli like touch or smell. The group has already begun building computer models of such networks, which could be applied to humans and eventually expanded upon.
“It turns out that there are remarkable convergences between the human brain and the fly brain, says Bock. “For example, the olfactory system is shockingly similar,” Bock says.
Read More: These Fruit Flies Aged Faster After Seeing Death
Mapping Neurons and Brain Functions
Having both a map of the whole fly brain and the sum of its parts should allow researchers to have a more sophisticated look at how such systems function. “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,” Gregory Jefferis, a co-author from the University of Cambridge in England, said in a press release. “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.”
Getting to this point was a long, arduous process involving hundreds of scientists. It started when Bock, in 2013 at the Janelia Research Campus of the Howard Hughes Medical Institute in Virginia, and colleagues removed a poppy-seed-sized fruit fly brain, immersed it in resin, let it harden, then shaved that block into many slices thinner than a human air, and then photographed each slice through an extremely high-resolution microscope.
That was the easy part. They repeated this process over a thousand times, resulting in millions of pictures. Then, the global team set to work identifying each separate neuron and synaptic connection. Finally, they used sophisticated computer software to put those pieces together into a three-dimensional map.
Bock says working on this project addresses the essence of why he chose this research field. “Each of us walks around every day with about 100 billion neurons working together, and we take it for granted. But somehow, it produces this thing we call our experience of life,” Bock says. “It’s a profound mystery, and it’s the thing that attracts most neuroscientists into the field.”
Key Stats From the Fly Brain Study
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76 laboratories and 287 individuals
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7,050 brain slices
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21 million microscope images
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139,255 neurons
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50 million chemical synapses
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8,453 cell types (there are now only 3,300 identified neuron cell types in the human brain)
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490 feet of neuronal “wiring”
Read More: 5 Of The World’s Largest Insects
Article Sources
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Before joining Discover Magazine, Paul spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
