Scientists have mapped an insect brain in more detail than ever before

There isn’t much uncharted territory in the wiring of an insect’s brain anymore.

All nerve cells — and virtually every connection between them — in a larval fruit fly brain have now been mapped, researchers report in March 10 Science, it is most complicated whole brain wiring diagram made so far.

Previously, the brain circuitry of only three organisms – a sea squirt and two types of worm – had been fully diagrammed to this resolution. But those creatures only have a few hundred neurons in their brains. The scientists conducting the new study wanted to understand far more complex brains.

fruit flies (Drosophila melanogaster) share a wide range of behaviors with humans, including integrating sensory information and learning. Larvae perform almost all the same actions adult flies – except for a few, such as flying and mating – but their brains are smaller, making data collection much faster (Sn: 7/19/18,

The idea for the project came about 12 years ago, says neuroscientist Marta Zlatik of the MRC Laboratory of Molecular Biology in Cambridge, England. At that time, she and her colleagues captured electron microscope images of whole larval fruit fly brains. They then stitched those images together in a computer and manually traced each neuron to create 3-D renderings of the cells. Finally, the team traced the connections where information is passed between cells, and even determined the sending and receiving end.

The researchers identified more than 3,000 neurons and approximately 550,000 connections, known as synapses.

Neurons transmit information to each other in circuits. A search for the connectivity patterns of neurons—not just directly connected partners, but links to linked cells and so on—revealed 93 different types of neurons. Classes corresponded to pre-existing groups characterized by size and function. And about 75 percent of the best-connected neurons were bound to the brain’s learning center, indicating its importance to learning in animals.

The researchers hope that this work will serve as a blueprint for fellow scientists studying brain circuitry. “Now we have a reference map,” Zlatik says.