The Human Brain Has a Dizzying Array of Mystery Cells

An international team of scientists has mapped the human brain in much finer resolution than ever before. The brain atlas, a $375 million effort started in 2017, has identified more than 3,300 types of brain cells, an order of magnitude more than was previously reported. The researchers have only a dim notion of what the newly discovered cells do.

The results were described in 21 papers published on Thursday in Science and several other journals.

Ed Lein, a neuroscientist at the Allen Institute for Brain Science in Seattle who led five of the studies, said that the findings were made possible by new technologies that allowed the researchers to probe millions of human brain cells collected from biopsied tissue or cadavers.

“It really shows what can be done now,” Dr. Lein said. “It opens up a whole new era of human neuroscience.”

When studying fresh brain tissue, the scientists attached glass tubes to the surface of individual cells to eavesdrop on their electrical activity, injected dye to make out their structure and finally sucked out the nuclei from the cells to inspect them more closely.

Rather than carrying out these procedures by hand, the researchers designed robots to work efficiently through the samples. The robots have inspected more than 10 million human brain cells so far, Dr. Lein estimated.

Some of the newly identified cells were found in layers of cerebral cortex on the brain’s outer surface. This region is essential for complex mental tasks such as using language and making plans for the future.

But the new studies reveal that much of the brain’s diversity lies outside of the cerebral cortex. A vast number of the cell types uncovered in the project lie in the deeper regions of the brain, such as the brain stem that leads to the spinal cord.

Adam Hantman, a neuroscientist at the University of North Carolina who was not involved in the study, said that the atlas would be a big help for some kinds of research, like tracing the development of the brain. But he questioned whether a catalog of cell types would elucidate complex behavior.

“We want to know what the orchestra is doing,” he said. “We don’t really care what this one violinist is doing at this one moment.”

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