Pioneering map of all the neurons in an adult brain

The first complete diagram of all the neurons in an adult brain and all the connections between them has been created. Due to the enormous complexity of this type of work, the brain chosen was that of a fly, which only has 139,255 neurons and about 50 million connections between them.

The achievement is the work of an extensive international consortium of nearly 300 scientists, called FlyWire Consortium, and has materialized in two studies, published in the academic journal Nature. One is titled “Neuronal wiring diagram of an adult brain” and the first signatory is Sven Dorkenwald, from Princeton University in New Jersey, United States. The other is titled “Whole-brain annotation and multi-connectome cell typing of Drosophila” and the first signatory is Philipp Schlegel, from the Laboratory of Molecular Biology of the Medical Research Council in Cambridge, United Kingdom. The consortium includes scientists from the University of Cambridge in the United Kingdom, the University of California in Los Angeles (United States), the University of Vermont in the United States and other entities.

The new neuron map, from a fruit fly, is the first of all the neurons in a brain of an adult animal endowed with advanced locomotion and visual capacity. In previous work, it was possible to create neuron maps of much smaller whole brains, for example, that of a fruit fly larva, which has only 3,016 neurons, and that of a nematode worm, which has 302 neurons.

The new map is a first and decisive step towards mapping other, larger, more complex brains. But it already represents a useful advance in itself, since the fruit fly is widely used in research as a model organism, so that the map of its brain can be used in studies on other brains, including the human.

3D reproduction of the set of about 140,000 neurons in the examined female fruit fly brain. (Image: FlyWire.ai (data); Philipp Schlegel / University of Cambridge / MRC LMB (rendering))

The entire brain of a fly measures less than a millimeter. The researchers started with a female brain cut into seven thousand slices each only 40 nanometers thick, previously scanned using high-resolution electron microscopy.

Analyzing more than 100 terabytes of image data to extract the shapes of some 140,000 neurons and 50 million connections between them is a task too large to be carried out exclusively by humans. For this reason, the researchers used the help of artificial intelligence, developed at Princeton University, to identify and map neurons and their connections with each other. The data was then carefully verified by human scientists, with the help of volunteers from the general public.

The FlyWire consortium has made the entire fly neuron map database available to the entire scientific community. (Fountain: NCYT by Amazings)