In a "tour de force", researchers imagine a whole brain of the fly in every detail | Science

For the first time, scientists have imagined the entire brain of Drosophila Drosophila melanogaster with enough detail to detect individual junctions, or synapses, between each neuron. The resulting image database could help researchers map the neural circuits that underlie each sniff, zoom and aerial maneuver in the behavior of a fly

"This dataset – and the opportunities that it creates – are without doubt one of the most important ones, "says Rachel Wilson, a neurobiologist at Harvard University, who was not involved in the new work. "Anyone interested in the world can download the dataset and determine if two neurons … speak to each other."

The brain of fruit flies of 100,000 neurons is elementary compared to some 100 billion neurons of our own skulls, but the fly is still "much more than this little point that you stray from your glbad of wine over dinner," says Davi Bock, neuroscientist at Janelia Farm Research Campus of Howard Hughes Medical Institute in As hburn, Virginia Some systems in the brain of flies – such as those that detect and remember odors – probably share "common principles" with those of humans, he says

to distinguish the characteristics of individual synapses, when A signal from one neuron flows into another. , Bock and his colleagues used an electron microscope, which can solve much finer details than a traditional optical microscope. They soaked the brain of a fly in a solution containing heavy metals, which bind to the membranes of neurons and proteins at the synapses. It made the brain look like a wad of noodles, each dark on the outside but white on the inside, Bock explains. Then a diamond knife cut the brain into about 7000 slices, each of which was hit with an electron beam from the microscope to create an image

The process required a camera capable of capturing 100 Frames per second, a robotic system to tape each slice of brain into place with nanoscale precision, and software to bademble the resulting 21 million photos. The result is a reconstruction that allows researchers to zoom in on the features of an individual synapse.

"This document is the absolute definition of a tour de force in terms of technical achievement," says neurobiologist Cornelia Bargmann of Rockefeller University in New York. She studies the nervous system of the nematode Caenorhabditis elegans ; a wiring diagram, or connectome, of its 302 neurons was published in 1986. To obtain a similar diagram for the brain of flies, researchers will have to use the new images to trace each neuron to each other neuron that he listens to. and speak through the brain.

Up to now, Bock and his team have done it for a small subset of neurons in a part of the brain involved in learning and memorizing odors called the mushroom. This initial project, described today in Cell gives new details on the well-studied olfactory system of the fly. For example, neurons that relay odor information to mushroom cells form unexpectedly tight bundles, which Bock's team is currently studying to find out how flies sample odors from their environments.

diagram of the fly brain, they will then need to combine this information with other technologies that record the brain activity of living flies. The strength of connections between neurons changes in different contexts and over time, notes Bargmann. "I've been working on an organism with a connectome for 30 years, and we're still discovering how this nervous system works."

But the technical capabilities described in the new paper suggest that it will soon be possible to map the connectome of a creature that is yet another evolutionary step closer to humans. "Since the fly works, the zebrafish is about the same order of complexity," says Bargmann. "I think we could get to vertebrates in not too long."