The human brain has a dizzying variety of mysterious cells | ET REALITY

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An international team of scientists has mapped the human brain at much finer resolution than ever before. He brain atlas375 million dollars effort started in 2017, has identified more than 3,300 types of brain cells, an order of magnitude more than was previously reported. Researchers have only a vague idea of ​​what the newly discovered cells do.

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

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

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

Still, Dr. Lein said the atlas was only a first draft. He and his colleagues have only sampled a small fraction of the 170 billion cells They are estimated to make up the human brain, and future studies will certainly uncover more cell types, he said.

Biologists first noticed in the 19th century that the brain was made up of different types of cells. In the 1830s, the Czech scientist Jan Purkinje He found that some brain cells had bursts of remarkably dense branches. Purkinje cellsas they are now known, they are essential for fine-tuning our muscle movements.

Later generations developed techniques to make other types of cells visible under a microscope. In the retina, for example, researchers found cylindrical “cone cells” that capture light. By the early 2000s, researchers had found more than 60 types of neurons in the retina alone. They were left wondering how many types of cells lurked in the deepest recesses of the brain, which are much harder to study.

With funding from the National Institutes of Health, Dr. Lein and his colleagues set out to map the brain by inspecting how brain cells activated different genes. At least 16,000 genes are active in the brain and are activated in different combinations in different cell types.

The researchers collected brain tissue from several sources, including people who had recently died and those undergoing brain surgery.

Studying fresh brain tissue, scientists placed glass tubes on the surface of individual cells to listen to their electrical activity, injected dye to distinguish their structure, and finally sucked out the cell nuclei to inspect them more closely.

Instead of performing these procedures by hand, the researchers designed robots to efficiently work with the samples. The robots have so far inspected more than 10 million human brain cells, Dr. Lein estimated.

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

But new studies reveal that much of the brain’s diversity lies outside the cerebral cortex. A large number of the cell types discovered in the project are found in deeper regions of the brain, such as the brain stem leading to the spinal cord.

The researchers found many new types of neurons, cells that use electrical signals and chemicals to process information. But neurons make up only about half of the brain cells. The other half They are much more mysterious.

Astrocytes, for example, appear to nourish neurons so they can continue to function properly. Microglia act as immune cells, attacking foreign invaders and pruning some of the neurons’ branches to improve their signaling. And the researchers also found many new types of these cells.

Researchers used some of the same methods to study the brains of chimpanzees and other species. By comparing results between species, the researchers investigated how the human brain evolved to differ from that of other primates.

Previous studies had suggested that the human brain could be distinctive thanks in part to the evolution of new cell types. But researchers were surprised to discover that all human brain cell types matched those found in chimpanzees and gorillas, our closest living relatives.

Within those cells, the researchers discovered a few hundred genes that became more or less active in humans than in other apes. Many of those genes are near genetic switches that turn genes on or off.

Dr. Bakken and his colleagues discovered that several of the genes that distinguish humans are involved in building connections between neurons, known as synapses.

“It’s really the connections (the way these cells communicate with each other) that differentiate us from chimpanzees,” said Trygve Bakken, a neuroscientist at the Allen Brain Institute who worked on the primate studies.

Megan Carey, neuroscientist at Champalimaud Center for the Unknown in Portugal, which was not part of the brain atlas project, said the research provided a staggering amount of new data for researchers to use in future studies. “I think this is a tremendous success story,” she said.

However, he also warned that understanding how the human brain works would not simply be a matter of cataloging each and every part of it down to its finest details. Neuroscientists will also have to take a step back and consider the brain as a self-regulatory system.

“There will be answers in this data set that will help us get closer to that,” Dr. Carey said. “We just don’t know what they are yet.”

Adam Hantman, a neuroscientist at the University of North Carolina who was not involved in the study, said the atlas would be helpful for some types of research, such as tracking brain development. 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 violinist is doing right now.”

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