What the needle critter looks like on the right is the larval version of the fruit fly on the left. Both scientists say the brain is remarkably complex, with different regions for decision-making, learning and navigation.
Ed Reschke / Getty Images
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Ed Reschke / Getty Images
What the needle critter looks like on the right is the larval version of the fruit fly on the left. Both scientists say the brain is remarkably complex, with different regions for decision-making, learning and navigation.
Ed Reschke / Getty Images
Scientists have created the first wiring diagram of an insect’s brain.
The brain, from fruit fly larvae, contained 3,016 neurons connected by 548,000 synapses, the team reported Thursday in the journal. Science.
Previous wiring diagrams, known as connections, were limited to worms and tadpoles with a few hundred neurons and a few thousand synaptic connections.
The fruit fly’s connection to the larvae is important because it is “closer in many respects to the human brain than anything else,” says Joshua Vogelstein, study author and associate professor of biomedical engineering at Johns Hopkins University.
For example, “There are regions that correspond to consultation, there are regions that correspond to doctrine, there are regions that correspond to navigation,” says Vogelstein.
But the challenges faced by scientists looking to produce a connected fruit fly show how far they still have to map the human brain, which contains more than 80 billion neurons and hundreds of trillions of synapses.
“The brain is the object of the body that makes us who we are.”
Researchers have focused on connections because the brain is so much more than a collection of neurons.
“The brain is the physical object that makes us who we are,” says Vogelstein. And to fully understand it, he says, you need to know how it’s wired.
Destined for a complete human connection is still many years away. In the meantime, the researchers hope that this new wiring diagram of fruit flies can offer clues about how all brains learn, for example, remember and control animal behavior.
The brain of the fruit fly larva, like the human brain, has a right and a left side. But when researchers dissected the connections in the insect’s brain, “one wonder” [was] how similar the right and the left are,” Vogelstein says.
In humans, the right and left sides of the brain can have very different wiring. Speech-encoding circuits tend to the left, for example, while face-recognition circuits tend to the right.
A “term first report”
The new map will help scientists study the ways in which learning changes in the brain, how brain wiring differs by sex, and how wiring changes during animal development.
“This is the first term of respect that we can apply to everything,” says Vogelstein.
This complete map of neural connections took a large team more than a decade to complete, and involved a lot of science.
The team of one brain began by minutely dividing the size of a grain of salt into a thousand thin sections.
“Don’t screw it up at all, because if you make one mistake, you basically throw out the whole brain and start over,” Vogelstein says.
The team used an electron microscope to take an image of each segment. Drawing connections from one neuron to another requires powerful computers and specialized computational tools.
Those tools are enough to track millions of visitors, Vogelstein explains, but not the trillions of connections found in the human brain.
So researchers at the Allen Institute in Seattle are working to make the next goal easier: designing a mouse connection. It’s also a huge challenge, says Nuno Maçarico da Costa, an associate researcher at the Allen Institute in Seattle, who was not involved in the fruit fly larvae study.
“We started by trying to describe the connectivity of a cubic millimeter of mouse cortex, which is like sand, but it has one billion connections — 100,000 neurons, and 4 kilometers of cables,” says da Costa.
It took just 12 days to carve out one tiny cube, which represents only about one-fiftieth of a complete mouse brain, he says.
Despite the difficulty, mapping more complex brains is worthwhile, da Costa says, because it ultimately helps scientists understand how the human brain can be affected by disorders like schizophrenia.
“If you break your radio,” says da Costa, “if someone has a radio record of your radio, they’ll be able to fix it in a better place.”
The human connection will also help scientists answer some basic questions, like how we learn and why we do the way we do, he says.
“Every idea, every memory, every movement, every thought that has ever been made is the result of the activity of neurons in your brain,” says da Costa. “And this action is the expression of this structure.”
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