White matter fibers form so-called tracts, bundles that follow specific anatomical routes. While many studies have examined the overall role of white matter, the cognitive functions supported by individual tracts have not yet been fully delineated.

Researchers at the University of Pennsylvania, the Lifespan Brain Institute (LiBI) and Children's Hospital of Philadelphia recently set out to better understand how white matter tracts support distinct brain functions. Their paper, published in Nature Human Behaviour, suggests that white matter tracts spanning more of the brain's cortical hierarchy connect regions with more distinct biological properties and support a broader range of mental functions.

"We already know a great deal about the cortex: for example, how different regions vary in their cognitive functions, myelination, gene expression and neurotransmitter systems," Joelle Bagautdinova, first author of the paper, told Medical Xpress.

"We also know a lot about the major white matter tracts that connect these regions. But these two areas of research have mostly been studied separately. White matter tracts, in particular, are still commonly grouped into broad anatomical categories (e.g., association, projection and commissural), which don't necessarily tell us much about what makes one tract different from another."