Just over a year ago, two scientific teams from the United States and the United Kingdom succeeded mapping the entire brain of the fruit fly larva, with its 3,000 neurons, a 12-year investigation that was later reported in the magazine Science. Previous research had also shown the mapping of a worm’s organ C. eleganswhich contains 302 neurons.
This week, it’s the magazine Nature the one who reports complete brain map of an adult specimen of fruit flies, several orders of magnitude more complex, with 139,255 neurons and around 50 million synapses connecting them. This is the first wiring diagram (or connectome) of this insect’s entire brain, Drosophila melanogastera typical model organism in biology.
This achievement was achieved thanks to an international collaboration of specialists, called FlyWire Consortium, which includes researchers from the UK, US, Australia, France, Germany, Israel, Korea, Philippines, Poland, Portugal, Puerto Rico, Switzerland and Taiwan.
While some groups have focused on connections, others have identified more than 8,400 cell typesincluding 4,581 new ones. Finally, other works in the collection shed light on how connectivity between specific neurons determines behaviors such as communication between brain regions or movement. In total, nine articles were published.
Understanding Bigger Brains
fruit flies They share 60% of human DNAand three out of four human genetic diseases have a parallel. Therefore, understanding their brains is another step toward understanding the brains of larger and more complex species, like humans, the authors point out.
“Your brain may seem tiny – it has about a million fewer neurons than the human organ – but a fruit fly can see, smell, hear, walk and fly. In addition, they socialize, navigate and learn from experience,” explains Sebastian Seung, researcher at Princeton University (United States) and co-director with Mala Murthy, from the research team of main article of this collection.
“Over the past decade, revolutionary advances have been made in our knowledge of the fly brain, and its connectome is fundamental. Although it is reconstructed from the brain of a dead specimen, it can provide us with valuable information on the functioning of a living brain,” he adds.
As Philip Shiu, a researcher at the University of California at Berkeley (United States) and leader of another of the new works, indicates, “it was not clear to what extent the connectome would allow us to predict activity neuronal, but we discovered that really allows us to predict and understand how the brain functions“.
First connectome of such a complex animal
The map was constructed from 21 million images extracted from a woman’s brain Drosophila melanogaster. Since there are differences in the neuronal structure of male and female flies, the researchers it is planned to also characterize a male organ in the future.
Thanks to a artificial intelligence model, the lumps and spots in these images have become a labeled 3D map. “We couldn’t have achieved this without automating the analysis. But at the final stage, we also need human intelligence, because AI still makes mistakes from time to time. A team of humans found and corrected these errors to produce the final connectome,” he says. Seung.
By comparing the brain diagram with previous, simpler diagrams, the researchers found that about 0.5 percent of neurons show developmental variations that could cause poor connections between them. Experts say it will be an important area of research to understand whether these changes are linked to brain disorders.
“There is no other complete adult animal brain connectome of this complexity,” says Murthy, director of the Princeton Neuroscience Institute. “We put the database accessible to all researchers in a way open and free. In the future, we hope it will be possible to compare what happens, for example, in the case of mental illnesses,” he adds.
Simulation of brain function
It is also the first map of complete brain wiring which predicts the function of all connections between neurons. There are two main ways in which these communicate across synapses: excitatory (which promotes the continuation of the electrical signal into the receiving neuron) or inhibitory (which reduces the likelihood that the next neuron will transmit signals).
The authors also used AI image scanning technology to predict whether each synapse was inhibitory or excitatory. “To begin to digitally simulate the brain, we need to know not only its structure, but also how neurons activate and deactivate each other,” he explains. Gregory Jefferis, researcher at the University of Cambridge (UK) and lead author of several of the studies.
“Without detailed knowledge of how neurons connect to each other, we will not have a basic understanding of what goes right in a healthy brain or what goes wrong in disease,” says John Ngai, director of BRAIN Initiative of the United States National Institutes of Health (NIH), which partially funded the FlyWire project.
Future avenues of research
Given that IAs connectomes become more affordable and faster to generate, you will likely see the number of these fly and other small animal wiring diagrams skyrocket in the years to come.
“Get a the mouse connectome and, over time, the human connectome will be incredibly valuable. “We can imagine a world in which we could simulate the brain of a mouse or, even more, that of a human being, and obtain fundamental information on the causes of various mental disorders and on the functioning of the brain”, insists Shiu.
“By modeling neurons better and better, we may be able to predict how the brain functions on a truly impressive scale,” concludes the scientist.
