Precisely mapped human brain reveals details never seen

Scientists at Harvard University in the United States, in partnership with Google and other affiliated scientists, designed a brain map that traces the varied shapes of 50,000 cells and 130 million connections – all made from a tiny piece of a woman’s brain. . The map, called H01 “Human Sample 1”, represents a milestone in the scientific search for increasingly detailed descriptions of a human brain.

Smaller than a sesame seed, the piece of brain was about a millionth the volume of an entire brain. It was removed from the cortex – the outer layer responsible for complex thinking – of a 45-year-old woman undergoing epilepsy surgery. After removal, the sample was quickly preserved and stained with heavy metals, revealing cell structures. It was then cut into more than 5,000 pieces and photographed with electron microscopes.

Then computer programs pieced together the segmented images resulting from the cuts and Artificial Intelligence programs helped the scientists to analyze them. A brief description of the resulting preview was published as a pre-print May 30 on the bioRxiv.org website. If you’re curious, the complete dataset is available for free online.

Scientific Community Reactions

The map thrilled neuroscientist Clay Reid of Seattle’s Allen Institute of Brain Science. In an interview with Science News, he said: “It is the beginning of something very exciting. It’s absolutely beautiful.” He is currently working on mouse and human brain maps. “It’s a magical moment in history,” he said.

But for now, researchers are just beginning to see what’s on the map. “Actually, we just dived into this dataset,” he told the Science News study co-author Jeff Lichtman, a developmental neurobiologist at Harvard University. Lichtman compared the brain map to Google Earth: “There’s gems there to be found, but no one can say they’ve looked at the whole thing.”

Symmetrical neurons found on the map.Source:  LICHTMAN LAB / HARVARD UNIVERSITY, CONNECTOMICS TEAM / GOOGLE / Reproduction

interesting finds

According to the scientist, fantastically interesting points have already emerged in the mapping. “When you have big datasets, suddenly these weird, rare things start to stand out,” he said. One of these curiosities concerns synapses – connection points where signals move between nerve cells.

Normally, message-sending axons touch a receiving dendrite only once. But in the new dataset, only about 90% of the connections were from these unique contacts. Some pairs of cells had little more than one contact, but the researchers found a few cells that connected multiple times, including one pair that was connected by no fewer than 19 synapses.

Several connections have been found in mouse brains, but not as abundantly as in this human sample. Fly brains can also have many connections between cells, but they are more dispersed than the human connections just described – explained neuroscientist Pat Rivlin, from the Howard Hughes Medical Institute in Ashburn, Virginia, United States, to Science News. Rivlin works on Project FlyEM, which creates maps of the fruit fly nervous system.

The images also revealed axons of neurons that send messages in elaborate, unusual and mysterious spirals – looking like coiled snakes. “We’ve never seen anything like it before,” Lichtman said. As researchers learned to look for these forms, more and more appeared.

Snake-shaped synapses, seen for the first time on the map developed by the study.Snake-shaped synapses, seen for the first time on the map developed by the study.Source:  LICHTMAN LAB / HARVARD UNIVERSITY, CONNECTOMICS TEAM / GOOGLE / Reproduction

speculations

“With the map, it becomes possible to analyze whether this large number of connections is common in the human brain,” said Reid. But after all, what are the super strong synapses doing? “These cells may be able to force their target cell into action in a powerful way,” Lichtman speculated. They may also be carrying out routine information efficiently, such as the result of a basic math score or that they need to stop at a red light – not yet known.

Molecular neuroscientist Seth Grant of the University of Edinburgh in Scotland pointed to Science News that while the map is a valuable tool, it only displays the anatomy of the brain. Further research will help clarify the function and composition of the molecules that drive its behavior. For now, the map is “a very exploratory tool,” he said.

What the maps will reveal remains to be seen. Lichtman was cautious when asked whether these maps will lead to a deep understanding of the brain: “I think the best we can do is describe,” he said, who hopes to soon reach a level of knowledge where he’s no longer surprised by what. see on maps.

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