Researchers have mapped a tiny portion of the human brain on an unprecedented scale, vividly describing each brain cell, or neuron, and the complex networks they form with other cells.
The groundbreaking brain map, created by Harvard and Google researchers, shows about 57,000 neurons, 9 inches (230 millimeters) of blood vessels and 150 million synapses, or the connection points between neurons.
Dr. Jeff Lichtman, a professor of molecular and cellular biology at Harvard University and co-leader of the 10-year project, said he couldn’t believe the detailed map when he first saw it. “I had never seen anything like this before,” he told Live Science.
The human brain is an extremely complex organ about 170 billion cells, including 86 billion neurons. Using magnetic resonance imaging (MRI), researchers have previously taken a look into the brain at a millimeter level. And more recently, advanced microscopy techniques have revealed details on a much smaller scale, improving our understanding of the brain’s inner workings.
Related: The most detailed map of the human brain ever contains 3,300 cell types
Well, with these microscopy methods and one artificial intelligence Using an AI system called machine learning, Lichtman and his colleagues created a 3D map of a piece of brain at the scale of a nanometer, or a millionth of a millimeter, showing an image of the organ at the highest resolution scientists have ever achieved.
The resulting cell atlas, described in the journal Science on May 9th, is also available for researchers to view online.
This map shows a tiny piece of brain with a volume of about 1 cubic millimeter – smaller than a grain of rice. An adult’s entire brain is a million times larger.
The brain fragment came from a 45-year-old woman who had undergone brain surgery to treat epilepsy. Doctors removed the piece from the cerebral cortex outermost part of their brain. After fixing the sample in preservatives, the researchers stained it with heavy metals to better see the cells. They then embedded the tissue in resin and cut it into more than 5,000 slices, each about 30 nanometers thick.
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“That’s about a thousandth the thickness of a strand of hair,” Lichtman said. The team scanned each of the slices with a high-speed electron microscope, which uses multiple beams of electrons to illuminate cells in the sample. They then sent the microscopy data to Google for further analysis using AI.
Google researchers used machine learning models to identify the same object in different microscopic images and then create a 3D representation of each object in all images. They then stitched together the renderings electronically to reconstruct the entire sample in three dimensions. The final 3D map contains a massive 1.4 petabytes, or 1 million gigabytes, of data.
“The volume and complexity of the data generated in this project required Google’s ability to develop state-of-the-art machine learning and AI algorithms to reconstruct the 3D connectome.” Vira Jaina senior scientist at Google who co-led the project told Live Science in an email.
The scientists’ detailed map contains several surprises. They found, for example, that some of the neurons’ outgoing wires, or axons, tangled into knots and formed whorls that Jain described as “mysterious but beautiful.” The team also found rare connections between neurons, with individual axons connecting at up to 50 synapses.
“We’re still studying the function of these connections, but they could explain how very fast reactions or very important memories are encoded,” Jain told Live Science.
It remains to be seen whether the vertebrae and super-strong synapses have anything to do with the tissue donor’s epilepsy or whether they would appear in the brains of people without the condition, Lichtman noted. He added that the team is currently studying brain tissue from a person with Parkinson’s, so it may begin to answer the question.
He added that it was unlikely that brain tissue samples from two people would look exactly the same, in part because the way the brain connects depends on the individual’s experiences.
Next, the team wants to map the entire brain of a mouse, which would be 500 times the size of this human brain sample. They start with the hippocampus, a key region for learning and memory.
“We have already begun the ambitious task,” said Lichtman.
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