Twenty-one teams of scientists around the world have collaborated to make the most detailed catalog yet of human brain cells.

The finding: the brain is made up of as many as 3,000 different kinds of cells and holds around 80 billion neurons.

“The only other large-scale biology problem of this scope is the Human Genome Project,” Andrea Beckel-Mitchener, deputy director of the U.S. National Institutes of Health’s BRAIN Initiative, said in a public statement announcing the result.

The study involved 250 scientists at 45 research labs and universities around the world.

Each team sequenced DNA from a specific part of the brain, then sent their results to computational biologists to be analyzed and interpreted.

Although all brain cells share the same DNA, each kind of cell uses a different configuration and makes a different group of proteins. The proteins determine a cell’s shape, which determines its function, and also what other kinds of cells it can communicate with.

For example, one team analyzed the molecular switches that turn different genes off and on in more than a million brain cells. They discovered more than 100 distinctly different cell types arrayed across 42 parts of the brain, far more of both than they expected to see.

The new knowledge will enable scientists to study the brain’s operations and illnesses in vastly more detail, which will allow far greater precision in diagnosing and treating illness. 

Using analytic techniques developed using mouse brains, the researchers scaled up the methods to analyze the brains of three adult male organ donors.

The sample is limited, the researchers acknowledge, but will grow as the research continues. 

Because of the time, cost, and other resources needed to adjust the research methods from mouse-scale to human-scale and run the 21 studies, the scientists had to choose between diversity and detail. 

“You can either go broad or you can go deep, but you can’t do both at the same time,” study co-leader Ed Lein at the Allen Institute for Brain Science told Wired magazine.

“Science is somewhat incremental, but people always want to advertise it as groundbreaking,” Amy Bernard, the director of life sciences at the Kavli Foundation, said to Wired. “This is both.”

TRENDPOST: This “atlas” of brain cells has instantly become a basic resource for neuroscientists and marks the beginning of a new area in neuroscience. Now that the atlas is online, it can be widely and freely used to study in far greater depth how the brain develops, functions, and ages; how things go wrong; and what kinds of therapies will be most effective for any given brain condition.