Superficial white matter fiber systems impede detection of long-range cortical connections in diffusion MR tractography

Reveley, Colin, Seth, Anil K, Pierpaoli, Carlo, Silva, Afonso C, Yu, David, Saunders, Richard C, Leopold, David and Ye, Frank Q (2015) Superficial white matter fiber systems impede detection of long-range cortical connections in diffusion MR tractography. Proceedings of the National Academy of Sciences of the United States of America PNAS, 112 (21). E2820-E2828. ISSN 1091-6490

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In vivo tractography based on diffusion magnetic resonance
imaging (dMRI) has opened new doors to study structure–function relationships in the human brain. Initially developed to map the trajectory of major white matter tracts, dMRI is used increasingly to infer long-range anatomical connections of the cortex. Because axonal projections originate and terminate in the gray matter but travel mainly through the deep white matter, the success of tractography hinges on the capacity to follow fibers across this transition. Here we demonstrate that the complex arrangement of white matter fibers residing just under the cortical sheet poses severe challenges for long-range tractography over roughly half of the brain. We investigate this issue by comparing dMRI from very-high-resolution ex vivo macaque brain specimens with histological analysis of the same tissue. Using probabilistic tracking from pure gray and white matter seeds, we found that 50% of the cortical surface was effectively inaccessible for long-range diffusion tracking because of dense white matter zones just beneath the infragranular layers of the cortex. Analysis of the corresponding myelin-stained sections revealed that these zones colocalized with dense and uniform sheets of axons running mostly parallel to the cortical surface, most often in sulcal regions but also in many gyral crowns. Tracer injection into the sulcal cortex demonstrated that at least some axonal fibers pass directly through these fiber systems. Current and future high-resolution dMRI studies of the human brain will need to develop methods to overcome the challenges posed by superficial white matter systems to determine long-range anatomical connections accurately.

Item Type: Article
Schools and Departments: School of Engineering and Informatics > Informatics
Subjects: Q Science
Depositing User: Marianne Cole
Date Deposited: 06 Aug 2015 14:22
Last Modified: 08 Mar 2021 15:00

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