(Paris) An international team has succeeded in mapping all the neurons and connections in the brain of the Drosophila fly, a major advance for neuroscience, the results of which were published Wednesday in Nature.
Published yesterday at 11:06 a.m.
“One in three humans in the world lives with a neurological or neuropsychiatric disorder […] and most of them are linked to ‘circuit disorders’, that is to say that something is not working correctly in the way neurons communicate with each other in the brain”, recalls John Ngai, director of the American institute NIH Brain Initiative.
However, “we know too little about the circuits of the human brain to be able to offer treatments,” he continued during a press conference presenting the complete “connectome” of Drosophila, a major step in understanding these mechanisms.
A connectome is a representation of neuronal connections in a brain, which describes how neurons interact with each other to form brain circuits. The term refers to the genome, the genetic material of an organism, the first decipherments of which revolutionized science and medicine.
“Google Maps” of the brain
It took hundreds of researchers from the “Flywire” consortium ten years to map the 140,000 neurons and 50 million synapses in the Drosophila brain.
This tiny fly, which flies around fruit in our kitchens, is an important model for neuroscience because its brain solves many problems similar to ours.
It is capable of sophisticated behaviors like walking and flying, learning, memory, navigation and even social interactions.
No bigger than a grain of sand, the brain of a fruit fly was first cut into 7,000 sections, then photographed using very high resolution microscopes and assembled to form a 3D image of the brain.
“We started by manually identifying the neurons, but we estimated that it would take more than 4,000 years of human work to produce the connectome,” says Gregory Jefferis of the Cambridge Molecular Biology Laboratory.
The consortium then called on artificial intelligence. “But the AI made errors in the reconstruction of the neurons and these had to be corrected manually,” relates Mala Murthy of Princeton University, co-founder of the consortium, which then “opened the data to the entire community neuroscientists working on different parts of the fly’s brain so that they can help us.”
Once the map was established, neuroscientists labeled the different types of neurons and connections. A bit like “Google Maps, but for the brain,” explains Mr. Jefferis.
“The raw connections diagram is a bit like having a satellite image of the Earth, showing streets, buildings, rivers. Annotating the neurons means putting the names of streets and towns, opening hours…” explains the researcher. “You need both the base map and these annotations for it to be really useful to scientists. »
Neuroscientists have defined more than 8,000 cell types, making it the largest atlas ever produced. They also used AI to predict the neurotransmitter of each neuron, and whether the connections are excitatory or inhibitory.
This work has already enabled several advances in the understanding of the visual, olfactory and motor functions of the fly.
But if this connectome is a “crucial milestone”, the task remains “immense” to understand how the brain works, warns Mr. Ngai.
“The function of most cell types in the fly brain is still unknown,” says Sebastian Seung, a neuroscientist at Princeton. Sebastian Seung highlights the need for “other types of measurements in living brains to understand how these complex circuits underlie behavior.”
Just as the sequencing of the genomes of small organisms led to the rapid development of the sequencing of mammalian genomes, the Drosophila connectome will serve as the basis for mapping more complex brains.
The human brain connectome – around a million times more complex than that of the fruit fly, with 86 billion neurons – is currently out of reach.
The next step is mapping the mouse brain, which the researchers hope to establish within five to ten years.
Related News :