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April 08, 2012

The Geometric Structure of the Brain Fiber Pathways

Recently, Science published a very interesting article:

ABSTRACT: The structure of the brain as a product of morphogenesis is difficult to reconcile with the observed complexity of cerebral connectivity. We therefore analyzed relationships of adjacency and crossing between cerebral fiber pathways in four nonhuman primate species and in humans by using diffusion magnetic resonance imaging. The cerebral fiber pathways formed a rectilinear three-dimensional grid continuous with the three principal axes of development. Cortico-cortical pathways formed parallel sheets of interwoven paths in the longitudinal and medio-lateral axes, in which major pathways were local condensations. Cross-species homology was strong and showed emergence of complex gyral connectivity by continuous elaboration of this grid structure. This architecture naturally supports functional spatio-temporal coherence, developmental path-finding, and incremental rewiring with correlated adaptation of structure and function in cerebral plasticity and evolution.

Interesting fragments from the paper:

"Geometrically, this configuration is highly exceptional ... This sheet structure was found throughout cerebral white matter and in all species, orientations, and curvatures. Moreover, no brain pathways were observed without sheet structure."

"Grid structure should restrict and simplify axonal path-finding compared with models that allow less constrained and less correlated connectivity within and between cerebral areas."

"Thus, the grid organization of cerebral pathways may represent a "default connectivity," on which adaptation of structure and function can both occur incrementally in evolution and development, plasticity, and function."