For the first time, all of a fruit fly's 139,000 neurons and the synapses that connect them (50 million) have been identified: “mechanisms” similar to those of our own brains, though ours have 87 billion neurons and 100 trillion synapses.
The “FlyWire Consortium", an international team of neuroscientists led by Princeton University (United States), which has been committed since 2018 to studying the brain’s “mechanisms” down to the smallest detail, has achieved an important goal: tracing out the complete map of the brain of Drosophila melanogaster, the fruit fly.
As reported in the scientific journal Nature, the researchers in the Consortium, comprising 76 laboratories and 287 researchers from different countries, snapped approximately 21 million images of over 7,000 extremely thin sections of the brains of female fruit flies, which were then analysed using an electron microscope with a resolution in nanometres (billionths of a metre). Afterwards, they used artificial intelligence to combine that enormous mass of data, not only on the 139,255 nerve cells that form the brain of Drosophila, but also on the 50 million connections (synapses) that carry stimuli and responses from one cell to the other. It is the first time that such a detailed and complete map has been created.
But why devote so much attention and such great financial resources to the brain of a fruit fly?
What might seem a purely descriptive task is, in truth, an essential undertaking, and one that is very difficult to accomplish. To give you an idea, until now, all that had been mapped were the neurons in the brain of a minuscule worm, C. elegans, which possesses only 302, and those of fruit fly larvae, which have about 3,000. The importance of this type of research lies in the fact that some of the mechanisms that allow fruit flies to function are similar to those of the human brain (which is composed, according to the most recent estimates, of about 87 billion cells and 100 trillion synapses).
We still know very little, however, about our brains, and we cannot precisely understand the nature of the majority of the disorders that affect them, beginning with neurodegenerative diseases, like Alzheimer’s and Parkinson's. A complete mapping of the fruit fly's brain could offer important contributions to this research. For this reason, the FlyWire Consortium researchers, who have published a suite of nine related papers in the same issue of Nature (relating to other aspects of the Drosophila brain as a whole), thus earning themselves the cover, have made the data they collected available to the entire scientific community, so that they can be used by anyone, allowing research to progress much more quickly.
60% of DNA shared with humans
To give an idea of the importance of this data, fruit flies share 60% of human DNA, including the genes for learning (and for jet lag).
What’s more, three out of four human genetic diseases have a parallel in these insects. Thus, understanding how a fruit fly's brain functions can, as we have said, become the jumping off point for deciphering the brains of much larger and complex species, like humans, as well.
It is no coincidence that studies of Drosophila (not all of them involving the brain) have led to six Nobel prizes, including the one awarded to Eric Wieschaus of Princeton University in 1995. As the authors of the studies published in Nature remind us, fruit flies age like we do, can become intoxicated if they come into contact with alcoholic substances, stay awake if given coffee, and serenade their partners. They even provided the green light for human space travel when, in 1947, NASA sent several up in a space ship. When they came back alive, they paved the way for astronauts.