Based on a human brain fragment, US researchers have created an extremely detailed 3D computer model of parts of the cerebral cortex. The reconstructed area is only one cubic millimeter in size, like the team led by Jeff Lichtman from the Center for Brain Science at Harvard University in the journal Science writes. Due to the enormous complexity of our brain, tens of millions of individual structures can be found even in this tiny section.
The model contains 57,000 cells (including around 16,000 neurons), 23 centimeters of blood vessels and 150 million synapses, as Lichtman and his team report. So-called glial cells, which, among other things, carry out support and supply tasks in the nervous tissue, can also be seen. You can also see myelin, the insulating layer around the processes of the nerve cells.
Such detailed images of the brain – including neurons and their connections – are important for understanding how the brain works. “The human brain is an extremely complex tissue. However, so far little is known about its cellular microstructure, such as the synaptic circuits,” writes the team. Disruptions in these circuits are likely linked to various brain diseases.
A tiny piece of the so-called temporal lobe of the cerebral cortex of a living person served as a template for the model. Brain surgeons removed the fragment from a 45-year-old woman to gain access to a specific area in the hippocampus during a surgical treatment for epilepsy. In purely mathematical terms, the removed fragment would fit 1,000 times into a cube with a side of one centimeter.
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The team led by neuroscientist Lichtman planed the tiny brain fragment into extremely fine slices, scanned each one with an electron microscope and assembled the cross-sectional images into a three-dimensional computer model. It is freely accessible on the Internet, so even interested laypeople can scroll through it with a little practice. The different cell types were first marked in the brain sections so that the researchers were able to look at individual neurons and their connections to other cells in the computer model.
The researchers have already gained initial insights with their 3D model. They counted twice as many glial cells as nerve cells in the area shown. The most common cell type is so-called oligodendrocytes. These cells belong to the glial cells and surround the so-called axons of nerve cells – i.e. the extensions of the neurons that are responsible for transmitting electrical signals – and form the insulating myelin layer there.
The researchers hope that other scientists will also use the new brain model. “Further studies using this application could provide valuable insights into the mysteries of the human brain.” Efforts to understand data on the connectivity of neural circuits are still in their infancy. “But this petabyte data set is a start.”