57 thousand neurons and millions of their connections on a map of a cubic millimeter of the brain

Harvard University and Google have teamed up to create a new map of the brain with an unprecedented level of detail. A 3D model produced by scanning a piece of human brain tissue has revealed a surprising number of neural connections and cells present.

A digital map of just one cubic millimeter of the human brain contains 57 thousand cells and 150 million synapses. Although it represents only one millionth of an organ, the amount of data required to process it is 1.4 petabytes. (one petabyte is equivalent to one million gigabytes). The scientists behind the project were surprised and, in their own words, “humbled” to encounter the complexity contained in this tiny clump of brain mass.

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To accomplish this feat, Harvard researchers removed tissue from the cerebral cortex of a 45-year-old woman during epilepsy surgery. The sample was cut into 5,000 slides, which were then analyzed and scanned using electron microscopes.

Google experts used this information to create machine learning models that could stitch each photo into a 3D map. According to Jeff Lichtman, a professor of molecular biology at Harvard, while the procedure may seem simple, it is extremely difficult to perform, and there are no records of similar attempts.

“By combining brain imaging with artificial intelligence-powered image processing and analysis, our teams reconstructed nearly every cell and its connections in this small volume of human brain tissue, about the size of half a grain of rice,” Google explains in its report. blog.

Neuron (white) with approximately 5000 axons (blue). Synapses are green flashes.

The map reveals details that were not previously observed in the structure of the brain. Among the highlights were several pairs of neurons that connected to each other with great strength across 50 synapses. Typically cells are connected to each other by only a pair of connections.