Many of us only think of fruit flies when the air above a neglected bunch of bananas suddenly becomes charged with activity, but a team of researchers from Johns Hopkins and the University of Cambridge have thought enormously – and also demonstrated exactly how they, the flies, think about everything. In an unprecedented scientific feat, the team managed created one synapse map per synapse from the brain of a fruit fly larva (Drosophila).
Prior to this achievement, only parts of insect brains had been reconstructed, said researcher Marta Zlatic from the University of Cambridge’s Department of Zoology and the MRC’s Molecular Biology Laboratory. Hyperallergic.
“Now, for the first time, we have a comprehensive view of circuit patterns in a whole larval insect brain as well as interactions between the two cerebral hemispheres and between the brain and the nerve cord,” Zlatic said. The brain of the fruit fly is smaller than a poppy seedand the new map shows the 3,016 neurons and 548,000 synapses (the gaps where communication between neurons occurs).
Due to the limitations of the technology, using electron microscopy to image whole brains and reconstruct their circuits – known as connectomes – has been an uphill battle. So far, fully synaptically resolved connectomes have only been mapped for much more basal organisms with several hundred brain neurons. The complex organization of the young fruit fly’s brain made recreating an order of magnitude more complicated for the team, led by Michael Winding of the University of Cambridge.
“The larva is a free-behaving child that needs to crawl and dig to find food, escape predators, cooperate with other larvae,” Zlatic continued. “They have many modes of locomotion, crawling, digging, rolling (equivalent to our walking, swimming, running). They are capable of complex forms of learning and have short and long term memory, they have to decide what to do then depending on the context and previous memories.
In order to map such a complex mind, the fruit fly’s brain was first sectioned into thousands of thin sections, and each was imaged by transmission electron microscopy. The resulting images were stitched together using specialized software developed by study co-author Albert Cardona. This created a 3D volume that one can navigate “like a 3D Google map, and manually trace neurons and annotate synapses,” according to Zlatic. The whole process took 12 years.
The leap from brain mapping of fruit fly larvae to brain mapping of a human is still huge, but Zlatic believes the work undertaken here is still a giant leap for understanding neural networks, writ large.
“Human brains are a lot bigger and have a lot more neurons, so it would take MUCH longer,” Zlatic said. “But we think the basic principles by which brains function, process information and select actions will be common across the animal kingdom. So, by understanding smaller brains, we can get a lot of information about larger brains. »
