57,000 neurons in 1 cubic mm

that it The most detailed work Of its kind, several teams around the world have been dealing with the topic of brain “mapping” for a dozen years. We call this a “neural network,” a map of connections between neurons — because it is in these connections, not in the neurons themselves, that the enormous complexity of the brain lies. In itself, Human Brain Project It has spent €600 million over a decade and generated thousands of searches, but the ultimate goal – a comprehensive map – remains science fiction.

As proof, this cubic millimeter, obtained from the cerebral cortex of a 45-year-old woman, represents only a millionth of the brain. But it is He is still able to reveal new surprises: neurons that coil on themselves to form ganglia, pairs of neurons that are almost twins of each other, and unexpected ways in which connections between neurons are created. the team From Harvard University The Google research team cut this piece into 5,000 “slices” – each 34 nanometers thick – which were then analyzed by electron microscopes.

The amount of information this represents, which is freely accessible online, is so large that only artificial intelligence programs can piece together these 5,000 slices to create a 3D map. But detailed verification by humans — looking for the inevitable errors that creep into the work AI does — could take years: For now, the researchers note in their paper: Published on May 10 By Science magazine, hundreds of neurons were examined, out of 57,000.

In total, the human brain contains between 85 and 100 billion neurons. But given that each neuron has multiple connections to its neighbors – and that the researchers identified an unprecedented 50 connections – the step is still high.