By Rose Eveleth
Posting in Cities
Mapping the brain's connections reveals a city grid like arrangement.
The human brain is made up of tens of billions of connecting nerve fibers carrying electricity and information. How those connection are organized has long interested neuroscientists - who long believed they were arranged randomly, tangled up like a big bowl of spaghetti. But new research has uncovered that these connections are not the mish mosh of wires researchers expected - instead, they're arranged in a highly structured pattern.
In a paper in Science today, researchers unveiled a brand new image of how the brain is connected. Rather than a mess of wires running willy nilly across your skull, human brains are organized through bundles of neurons much like a computer's ribbon cable. These bundles travel across the brain like a city grid, traversing in all directions.
"Before, we had just driving directions. Now, we have a map showing how all the highways and byways are interconnected," said author of the paper Van Wedeen in a press release. "Brain wiring is not like the wiring in your basement, where it just needs to connect the right endpoints. Rather, the grid is the language of the brain and wiring and re-wiring work by modifying it."
Mapping the brains connections is difficult. The traditional method is to track where the water goes in the brain as it diffuses through tissue. Researchers got this image using a powerful magnetic resonance imaging machine (MRI) that scanned and visualized the networks. This scanner tracks water too, but is better at looking at where fibres cross one another. The scanner, located at Massachusetts General Hospital, can generate images that are ten times more detailed than the conventional MRI machine.
This city-grid style arrangement makes sense when you think about the evolution of the brain, Weeden argues."Try going into your basement and randomly rewiring your house," he told New Scientist. "In a grid structure, it's much easier to imagine changes in the developmental code producing adaptive changes in behavior." If the brain were really a mash of random connections, mutations would be far less likely to lead to changes for natural selection to act upon.
Practically, mapping the brain this way could provide an easier way for doctors and neuroscientists to compare studies - using something like a coordinate system to pinpoint abnormalities or observations. It could also provide a structure on which researchers could grow new brain tissue.
There are, of course, limitations to this image. Weeden was only able to resolve the grid for about a quarter of the human brain, mostly in the deepest parts. Some researchers think that their model is oversimplified, and that while the grid may exist, it is combined with other, crisscrossing connections as well. To verify the grid, scientists could stain brain tissue samples in animals and build a three dimensional reconstruction that way.
Weeden agrees that the work needs to be refined and verified, but he's excited about where it's going. "“The functional significance of this is an open question,” Wedeen told Nature, “but I find it hard to believe that it doesn’t have an answer.”
via: New Scientist
Image: Van Wedeen, M.D., Martinos Center and Dept. of Radiology, Massachusetts General Hospital and Harvard University Medical School
Mar 29, 2012