Scientists at Google and the Janelia Research Campus in Virginia have published the largest high-resolution brain wiring map showing 20 million synapses connecting about 25,000 neurons in the brain of a fruit fly.
This model is an important milestone in the field of connectomics - the field of neuroscience, the subject of which is the connection (structural connections of the brain). The map shows about a quarter of the fruit fly's brain. To date, only one organism has been fully mapped - the roundworm C. elegans.
Connectomics has a controversial reputation in the world of science. Its advocates argue that it helps connect the physical parts of the brain with specific behaviors in organisms, a key goal of neuroscience. The critics' position is that connectomics has not yet made a single major discovery, and the work of scientists in this direction is the misuse of resources that could be directed to the study of other things.
“The map is without a doubt a technical miracle,” says Mark Humphries, a neuroscientist at the University of Nottingham. "By itself, it will not answer pressing scientific questions, but it can show us some interesting riddles."
The first step in creating the map was slicing the fruit fly's brain into slices only 20 microns thick - a third the width of a human hair. The size of an insect's brain is comparable to that of a poppy seed. However, fruit flies exhibit complex behaviors and even have mating dances.
The brain pieces were then visualized by bombarding them with beams of electrons from a scanning electron microscope. The resulting data contains about 50 trillion three-dimensional pixels (voxels). Google said it took scientists from Janelia two years and hundreds of thousands of hours to create a 3D map, checking the route of each of the 20 million synapses.
In total, the fruit fly's brain contains 100,000 neurons, while the human brain contains about 86 billion. This speaks to how far we are from creating a map of our own neural pathways.