March 30, 2012
Brain’s Nerve Fibers Mapped Into A Grid
Researchers have mapped brain nerves and have found them to be laid out in a three-dimensional grid. Mapping out these nerves will provide a greater insight into the inner-workings of the brain, as well as allow doctors to more precisely diagnose psychiatric and neurological disorders.
Van Wedeen, MD, of Massachusetts General Hospital led the research team who conducted this study. The results have been compared to a “bowl of spaghetti," a “chess board," and “a New York City grid” as the map lays out in colorful detail where every nerve is connected and interconnected.
However, other scientists wonder if Wedeen and his team have discovered the basic organizational structure of the brain or simply a map of nerve connections.
Scientists and researchers have for years tried to map the brain to understand the way it is laid out and organized. These brain mappers often used a technique called diffusion tensor imaging, which tracks the diffusion of water through the brain´s tissues to follow the fibers in the brain. Using this method, scientists are able to see how one region of the brain connects with one another.
Wedeen´s research, however, combined the use of MRI with diffusion tensor imaging a method called diffusion spectrum MRI. While also able to track the movement of water through brain fibers, diffusion spectrum MRI excels in highlighting where each fiber crosses one another. This technique shows several sheets of parallel fibers running 90 degrees to one another, resembling a piece of woven fabric. Researchers take these sheets and arrange them at right angles to create the three dimensional grid.
This three dimensional grid is more obvious in maps of lower primates. However, the higher one climbs up the evolutionary ladder, the more folds and curves are involved in the maps. Despite these complexities, the underlying grid remains the same.
Such a grid explains how brains are wired. Wedeen believes the way the grid is laid out and which way the fibers run are decided in the earliest stages of embryonic development. By following simple developmental rules and biochemical signals, these fibers are able to grow and connect at the proper place, much like the New York City Street system.
In addition to understanding how the brain works, this grid could also explain how the brain has evolved over the years.
“Try going into your basement and randomly rewiring your house,” Wedeen says. “In a grid structure, it´s much easier to imagine changes in the developmental code producing adaptive changes in behavior.”
Some scientists doubt the grid as a means of explaining the entire organizing structure of the brain. As the brain is such a complex and sophisticated object, these scientists worry applying such a simple theory to the entirety of the brain may be overgeneralized. What has these scientists concerned is the diffusion spectrum MRI technique used to map these nerves. Diffusion MRI can´t detect the nerve fibers directly, so if a fiber crosses at an extreme angle the fiber may have gone undetected.
“This is not a microscope,” says Marsel Mesulam of Northwestern University in Chicago, who studies how neural networks are affected by dementia and other cognitive disorders. “We´re looking at reconstructed images based on the movement of water molecules in a magnetic field.”
Wedeen remains confident in his research, saying a second diffusion imaging technique gave similar results.
On the Net: