Images reveal, in detail, a single cubic millimeter of the human brain; see | Technology

Neuroscientists at Harvard University in the United States have revealed detailed images of a single cubic millimeter of the human brain. The work of almost a decade is the largest and most detailed reproduction of the organ to date, according to information from the Science Alert website. The image, of a single fragment of the brain, measuring 1 millimeter on each side, is more than 57,000 cells, 150 million synapses and 230 millimeters of ultra-thin veins.

“The word ‘fragment’ is ironic,” said Harvard neuroscientist Jeff Lichtman. “A terabyte is, to most people, gigantic, but a fragment of a human brain – just a tiny bit of human brain – is still thousands of terabytes,” he added.

The reconstruction was based on a sample of human brain excised from a patient with epilepsy during surgery to access an underlying lesion. The sample was fixed, stained with heavy metals to accentuate the details, embedded in resin and sectioned into 5,019 slices, with an average thickness of 33.9 nanometers, collected on adhesive tape.

The researchers used high-throughput electron microscopy to visualize this small piece of tissue in detail, generating 1,400 terabytes of data. This data was then analyzed with specially developed algorithms, generating, the researchers say, “a 3D reconstruction of nearly every cell and process in the aligned volume.”

This reconstruction, called H01, has already revealed some unprecedented details about the human brain. The team was surprised to note that glia, or non-neuronal cells, outnumbered neurons in the sample, and the most common cell type was oligodendrocytes – cells that help coat axons with protective myelin, a fat-rich substance that involves these structures and helps with connection speed.

Each neuron had thousands of relatively weak connections, but researchers found rare and powerful sets of axons connected by 50 synapses. And they found that a small number of axons are organized into unusual, extensive spirals.

Because the sample was taken from a patient with epilepsy, it is unclear whether these features are normal but rare features of the human brain, or are linked to the patient’s disorder. Either way, though, the work revealed the vast breadth and depth of the chasm of understanding the brain.

Brain studies

The image represents a giant leap in understanding the notoriously complex human brain. Throughout the animal kingdom, the functions performed by most vital organs are more or less the same, but the human brain is in a league of its own.

Each human brain contains billions of neurons, firing signals through trillions of synapses, the command center from which the human body functions.

A deeper understanding of how this organ works would provide profound benefits to studies of brain function and disorders, from injuries to mental illness.

To that end, Lichtman and colleagues have been working on what they call a “connectome” — a map of the brain and all its connections that can help us better understand when those connections are distorted.

The current objective of the project is to reproduce an entire mouse brain. The next step in the team’s work involves trying to understand the formation of the mouse hippocampus, a region of the brain heavily involved in learning and memory.

“There is a level of understanding about brains that currently doesn’t exist. We know about the external manifestations of behavior. We know about some of the molecules that are disturbed. But among the wiring diagrams, until now, there was no way to see them. Now, there is a way,” Lichtman concluded.

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