How do you imagine your brain? Is the way how nerve fibers wire together in the brain as sprawling as a bowl of spaghetti? Van J. Wedeen and colleagues revealed that the interconnection of brain resembled a uniformly grid-like structure rather than a tangle of wires. Bringing a high resolution of wiring pattern of the brain, this study became a landmark of neuroanatomy.
Using diffusion magnetic resonance imaging (diffusion MRI) to reveal the location of nerve fiber by detecting water movement inside, researchers are able to distinguish differently oriented fibers within the same location. This is critical for discovering the grid structure. In this study, brains from different species were scanned, including postmortem brains from four kinds of primates and also brain from living human. And astonishingly, the same grid-like patterns, similar to the woven sheet of fabric, were obtained. The nerve fibers are organized parallel, crossing with each other in two directions to form 2D sheets, and in the third direction, parallel fibers lie perpendicularly to these sheets. All these sheets stack together and form the grid connectivity continuously and consistently through the entire brain.
Fig. 1: Details from diffusion spectrum imaging (DSI) show fabric-like 3D grid structure of connections in monkey brain.(Image courtesy of NIH Human Connectome Project).
Van J. Wedeen and colleagues further hypothesize that the highly curved 3D gird structure of fiber pathways derive from the three primal axes of development. And the grid structure would restrict and simplify the axonal path-finding since a nerve fiber could only turn in four directions, left or right, up or down. What’s more, the grid structure occurs in different species but with different degrees of brain complexity, suggesting that the grid structure could be modified by evolution. With a deeper analysis of the grid structure, it may also help to understand more about brain connectivity and brain disorders in the future.
Wedeen, Van J., Douglas L. Rosene, Ruopeng Wang, Guangping Dai, FarzadMortazavi, PatricHagmann, Jon H. Kaas, and Wen-Yih I. Tseng. "The geometric structure of the brain fiber pathways." Science 335, no. 6076 (2012): 1628-1634.