Massachusetts, US

Scientists from Harvard University, in collaboration with Google's machine learning experts, have meticulously reconstructed a wiring diagram of a minute section of the human brain, an incredibly complex and vital organ that serves as the command centre for the nervous system.

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This groundbreaking endeavour has revealed new details of the structure that is comprised of billions of neurons to transmit information through electrical and chemical signals.

The study reportedly focused on a minuscule cubic millimetre of healthy brain tissue extracted from the cortex of a 45-year-old woman undergoing surgery for epilepsy, a neurological disorder characterised by recurrent seizures, which are sudden, brief changes in the brain's electrical activity.

Despite the small size of the tissue, it was a monumental task to map out its wiring diagram for neural circuitry, cellular connections, and vascular support. Using electron microscope images of over 5,000 tissue slices, the researchers unveiled a staggering 57,000 individual cells, 23 centimetres of blood vessels, and 150 million neural connections. 

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Professor Jeff Lichtman of molecular and cellular biology at Harvard University said, “The aim was to get a high-resolution view of this most mysterious piece of biology that each of us carries around on our shoulders."

“The reason we haven’t done it before is that it is damn challenging. It really was enormously hard to do this," said Lichtman added. 

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By employing machine learning algorithms, the team meticulously traced the pathways of neurons and other cells through the tissue sections, a process that would have taken humans years to accomplish manually. The resulting dataset, comprising 1.4 petabytes of data, revealed numerous findings and challenged existing understandings of brain structure and function.

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“We found many things in this dataset that are not in the textbooks,” Lichtman said. 

Pyramidal neurons

In the study, one of the intriguing discoveries were of pyramidal neurons that exhibited an unexpected symmetry in their dendritic branching. In addition to this, the presence of tightly wound axon bundles gave details into signal transmission within the brain. 

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While the prospect of mapping the entire human brain remains daunting, the team is embarking on a collaborative effort with Google to reconstruct the wiring of an entire mouse brain. This endeavour aims to elucidate the neural circuits governing behaviour and decision-making. 

“There are really wonderful opportunities, if you have a whole mouse brain, to get insight into free will, even... You know, a mouse is not a robot," Lichtman said. 

(With inputs from agencies)