The first complex brain mapped: that of a fly

The first mapping of a complex brain, the brain of a fly: 140,000 neurons, 54 million synapses: a feat, enough to now test all neurological models, and simulate the functions of the brain.

Mathilde Fontez, editor-in-chief of the magazine Epsiloon,(New window), evokes today a real feat which has just been announced in the prestigious scientific journalNature.

franceinfo: DResearchers have mapped an entire brain, the complex brain of a fly?

Mathilde Fontez: Yes, it is a tour de force that was achieved by this consortium of nearly 300 researchers: all the neurons of a brain and all the synapses – these connections between neurons – were photographed and labeled one by one.

Before that, brains had already been mapped, but it was that of a worm, the worm C. elegans: 302 neurons. And that of a fly larva: 3000 neurons. This is the brain of an adult fly: it has 140,000 neurons and 54 million synapses. This is the first map of a complex brain.

Is the fly considered a complex animal?

Yes, it is a sophisticated animal: capable of learning, decision-making, social interactions. Mapping your brain seemed inaccessible only a few years ago. It took patience – the researchers took 21 million images with an electron microscope, with resolution in the nanometer range.

And these researchers used artificial intelligence to reconstruct the structure of the brain in 3D from there. The brain in all its details, in all its connections: researchers call this the “connectome”. With this map, it becomes possible to identify the important neurons, the nodes of the network. We can follow the entire information circuit in the brain.

We hope to better understand how flies think?

Yes, this map is now available to researchers. They can use it to test their models, verify, interpret their experiments. This has already started: 9 scientific articles were published at the same time as the map. They began to look at taste processing pathways: for example, how sugar or water activates the feeling of hunger in the fly, and triggers movement.

Vision too: they confirmed that flies see in front of them and the sky above their heads at the same time. Navigation: they guide their flight in relation to the light of the Sun. We will soon know everything about flies! And more generally how a brain works – the fly is a model animal, it is not that far from us. We have 60% of genes in common.