A decade ago, a small sample of brain tissue, no bigger than a grain of rice, arrived at Dr. Jeff Lichtman’s lab at Harvard University. This tiny piece, measuring just 1 cubic millimeter, held 57,000 cells and 150 million connections between those cells. It was an incredibly small but crucial part of the brain’s complex communication system.

Over the past ten years, Dr. Lichtman and a team of Google scientists have worked together to turn this tiny piece of brain tissue into something ex...