Inside the head of a fruit fly larva

The set of neurons in a Drosophila brain.

The most detailed insect brain map to date, that of a fruit fly larva (Drosophila ), was made by American and British neuroscientists.

This map, called a connectome, is a complete map of the neural connections of the insect brain 3mm in length and d an adult weight of 0.54 mg.

According to the researchers, this landmark work in the field of neuroscience brings scientists closer to a true understanding of the mechanism of thought, since the Drosophila brain is comparable to that of humans and can serve as a model.

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If we want to understand who we are and how we think, we must understand the mechanism of thought, explains in a press release the main author of the study , Joshua T. Vogelstein, biomedical engineer at Johns-Hopkins University. And the key to this understanding is knowing how neurons connect to each other.

The first attempt to map a brain – a 14-year roundworm study – started in the 1970s resulted in a partial map and a Nobel Prize, the statement noted. from Johns-Hopkins University.

Several partial connectomes have since been mapped, including those of the fly, mouse, and even human. These works, however, represent only a tiny part of their brains.

More complete connectomes have only been generated for small species whose bodies have only a few hundred or a few thousand neurons, such as the larvae of ascidians or marine annelids.

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This was before the present work of researchers from Johns-Hopkins University and the University of Cambridge, details of which are published in the journal Science (in English) which reconstructs in 3D the larval brain of Drosophila melanogaster, based on electron microscopy.

The complete insect connectome includes 3,016 neurons and 548,000 synapses.

The researchers created the high-resolution images of the brain and studied them one by one to find the individual neurons, by rigorously tracing each of them and linking their synaptic connections.

The Drosophila larval brain has an order of magnitude larger neurons, an even larger scale of synapses, and a complex brain organization. This insect brain connectome will be an enduring resource, providing a foundation for a multitude of theoretical and experimental studies, the researchers note in the study.

Due Due to technological constraints, imaging whole brains with electron microscopy and reconstructing circuits from these datasets was a challenge, they continue.

The team chose the fruit fly larva because, for an insect, this species shares much of its basic biology with humans, including a comparable genetic base that exhibits behaviors of insects. learning and decision-making, making it a useful model organism in the field of neuroscience. And for practical reasons, its relatively compact brain can be imaged and its circuits reconstructed within a reasonable time.

Also, work carried out over twelve years on Drosophila larvae has shown circuit characteristics that are strikingly reminiscent of machine learning architectures.

This success may therefore inspire new artificial intelligence systems in the coming years. What we learn about the code of fruit flies will have implications for the code of humans, Vogelstein said. That's what we want to figure out: how to write a program that leads to a human brain network.