What looks like a pinhead on the right is actually a larval version of the fruit fly on the left. Both have very complex brains, with different areas dedicated to decision-making, learning and navigation, scientists say.
Ed Reschke/Getty Images
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Ed Reschke/Getty Images
What looks like a pinhead on the right is actually a larval version of the fruit fly on the left. Both have very complex brains, with different areas dedicated to decision-making, learning and navigation, scientists say.
Ed Reschke/Getty Images
Scientists have created the first detailed wiring diagram of an insect’s brain.
The brain of a fruit fly larva has 3,016 neurons connected by 548,000 synapses, the team reported Thursday in the journal. Science.
Previous wiring diagrams, called contomes, are limited to worms and worms with several hundred neurons and several thousand synaptic connections.
The fruit fly larval connector is an important advance because it is “closer in many ways to the human brain than any other,” said Joshua Vogelstein, a study author and associate professor of biomedical engineering at Johns Hopkins University.
For example, “there are areas that correspond to decision-making, there are areas that correspond to learning, there are areas that correspond to navigation,” Vogelstein says.
But the challenges scientists face in extracting the connectome from fruit fly larvae show how far they have to go to map the human brain, which contains more than 80 billion neurons and hundreds of trillions of synapses.
“The brain is the physical object that makes us who we are”
Researchers focused on connotomes because the brain is much more than a collection of neurons.
“The brain is the physical entity that makes us who we are,” Vogelstein says. “And in order to fully understand this object, you need to know how it is wired,” he says.
Mapping the complete human connectome will take many years. So the researchers hope that this new fruit fly wiring map can explain how the entire brain learns, such as memory and control of the animal’s behavior.
A fruit fly larva has a right and left brain just like a human brain. But when the researchers mapped the connections in the insects’ brains, “it was surprising how similar the right and left sides were,” says Vogelstein.
Humans may have different wiring between the right and left brains. Circuits involved in speech are usually on the left, for example circuits that recognize faces are on the right.
“First historical reference”
The new map will help scientists study how learning changes the brain, how the brain’s wiring differs by sex, and how wiring changes during an animal’s development.
“It’s the first historical reference that you can use to compare everything else,” Vogelstein says.
This large-scale mapping of neural connections took a large team and science over a decade.
The team began by cutting a brain as small as a grain of salt into thousands of very thin pieces.
“You don’t mess it up at all, because if you make a mistake, you basically have to throw out the whole brain and start all over again,” Vogelstein says.
The team used an electron microscope to take pictures of each slice. Tracing connections from one neuron to another required powerful computers and special computational tools.
These tools are good enough to track millions of connections, Vogelstein explains, but not the billions of connections in the human brain.
Researchers at the Allen Institute in Seattle are working on a simple goal: to map the mouse contextome. That’s a big challenge, says Nuno Macarico da Costa, a research associate at the Allen Institute in Seattle who was not involved in the fruit fly larvae study.
“We started by mapping the connectivity of a cubic millimeter of mouse cortex, which is a grain of sand but has billions of connections—100,000 neurons and 4 kilometers of wiring,” says da Costa. .
It took him 12 days to cut out this tiny cube, which is about five-hundredth the size of a mouse’s entire brain, he says.
Despite the challenge, mapping more complex brains is worth the effort, Da Costa says, because it could help scientists understand how diseases like schizophrenia affect the human brain.
“If your radio breaks,” says da Costa, “if someone has a wiring diagram for your radio, they’re in a good position to fix it.”
The human connector also helps scientists answer some fundamental questions, such as how we learn and why we behave the way we do, he says.
“Every idea, every memory, every movement, every decision you make comes from the activity of neurons in your brain,” says da Costa. “And this action is a reflection of that structure.”
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