He said this was not yet a proof of principle that scientists could indeed reconstruct the human brain, which contains 85 billion or more neurons, but that it was a first step.

Cori Bargmann, co-director of the new Kavli Neural Systems Institute at Rockefeller University, who has been intimately involved with the Brain Initiative, also a long-term research program, said the report represented an “amazing tour de force” in its accumulation of data.

But, she said, the “simulations are in their infancy,” and therefore what this means for the larger goals of reconstructing a whole brain is unclear. “They built a 747, and it’s taxiing around the runway,” she said. “I haven’t seen it fly yet, but it’s promising.”

The reconstruction that Dr. Markram envisions is a research tool that would digitally encode some characteristics of neurons and their connections that are common to all brains. It is not the futuristic dream of uploading a human personality to a computer.

To build a digital version of the portion of rat brain, researchers did not record the details of every single cell. They used the data from some cells to inform what the whole would look like. Then they simulated certain kinds of brain activity and found that the reconstruction acted like the living tissue. All the data for the reconstruction will be available for other scientists.