A fragment map of the human brain reveals its astonishing complexity for the first time, while providing new evidence of the anatomical structure of the brain and the way it functions.
The map is the culmination of years of work by scientists to locate the vast network of cells and connections within the sample, taken from the brain of a patient undergoing surgery to prevent severe epileptic seizures nearly a decade ago.
Although the specimen is a tiny fraction of an inch – about half the size of a sesame – it contains more than 50,000 brain cells, or neurons, and about 130 million thread-like axons that transmit signals between them. But this is only one-millionth of the volume of the entire human brain, which is estimated to contain about 100 billion cells.
Can be explored in detail via interactive map online neuroglancer graphic interface, which was developed with the aim of displaying complex images of brain tissue. It is now possible to see the various ways that the many neurons and axons of the human brain are effectively connected by making tissues invisible and revealing dense networks.
“You can think of the brain like a bowl of spaghetti,” said Dr. Professor of Molecular and Cellular Biology at Harvard University. Jeff Lichman, who led the project. “We cut it into very thin images and then traced each strand of pasta.”
The Neuroglancer interface can be accessed and explored by anyone.
“When you see things you couldn’t see before, it gives you a chance to think about things that are beyond your imagination,” he said. “It gives us ideas of a world that was foreign to us… now we’re starting to see what it looks like.”
The sample was taken from the temporal lobe of the patient’s neocortex, an external region of the brain’s “gray matter” associated with hearing and memory. After it was surgically removed, he and his colleagues preserved it in a type of resin and stained it with heavy metals to reveal its cellular structure. They then used an automated diamond knife to cut the samples into more than 5,000 slices, each a thousand times thinner than a human hair, and imaged them with an electron microscope. The images were processed by artificial intelligence and “proofread” by human experts to map all neurons and axons in 3D and color — resulting in the largest dataset ever for medical imaging, Lichman said. .
Harvard neuroscientist Alex Shapson-Coe, a member of Lichtman’s lab and lead author of a project over the years, has yielded 1.4 petabytes of data — nearly 100 times more than all the information stored in the E Library of Congress. new study on the project. processing the data would have exceeded the combined computing power of Harvard University, and so the scientists turned Google — one of the few organizations with enough computational capacity to help, he said.
New ideas from the thinking part of the human brain have already provided new insights. One is that some axons can connect to individual neurons more than a dozen times, while most can only connect once. Lichtman speculates that many of these connections may indicate memories or skills that have been “reinforced” by repeated use, such as learning to brake at a red light, for example.
“If you’re driving a car and you see a red light, you’re not thinking that you have to lift your foot, take it off the gas pedal, and put it on the brake,” he said. “You’re doing it automatically.”
The map also revealed several “mirror neurons” within the brain, where two brain cells near each other point in opposite directions; and curious coiled bundles of axons. Neither structure has been observed before, but it is not yet known what they do, Schapson-Coe said.
They hypothesized that the new map could be used to reveal differences in the brains of people with mental illnesses, such as schizophrenia, which are thought to be caused by changes in brain structure.
The new map comes as scientists grapple to figure out how the human brain creates consciousness, in addition to its automatic functions such as controlling breathing and blood pressure.
“What is an idea? How does creativity work? We don’t fully understand how learning works and the mechanisms for recalling memories are even more mysterious,” said Seth Grant, professor of molecular neuroscience at the University of Edinburgh in the United States. he said. State.
Grant, who was not involved in the project, explained that the structure of the specimen was probably representative of the brain’s entire neocortex.
“This will be a useful reference resource for future studies that examine the differences between individual brains,” he said in an email.
But knowing only the “wiring diagram” of the brain revealed by its structure would not be enough – scientists also had to understand the molecular structure of its myriad connections, which were now known to have many different types, he said.
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