Mapping of functional areas in the human cortex based on connectivity through association fibers

Abstract

In the human brain, different regions of the cortex communicate via white matter tracts. Investigation of this connectivity is essential for understanding brain function. It has been shown that trajectories of white matter fiber bundles can be estimated based on orientational information that is obtained from diffusion tensor imaging (DTI). By extrapolating this information, cortical regions associated with a specific white matter tract can be estimated. In this study, we created population-averaged cortical maps of brain connectivity for 4 major association fiber tracts, the corticospinal tract (CST), and commissural fibers. It is shown that these 4 association fibers interconnect all 4 lobes of the hemispheres. Cortical regions that were assigned based on association with the CST and the superior longitudinal fasciculus (SLF) agreed with locations of their known (CST: motor) or putative (SLF: language) functions. The proposed approach can potentially be used for quantitative assessment of the effect of white matter abnormalities on associated cortical regions.

Figure 1.

Probability mapping of cortical areas associated with the CST, IFO, ILF, FMa, FMi, SLF, and UNC. The color represents probability as indicated by the color bar, where “1” indicates 100% reproducibility (all 28 subjects have a connection to the pixel). L and R attached to the abbreviated tract names indicate left and right hemisphere. Abbreviations are: CST: cortitospinal tract; FMa: forceps major; FMi: forceps minor; IFO: inferior fronto-occipital fasciculus; SLF: superior longitudinal fasciculus; and UNC: uncinate fasciculus.

Figure 2.

Probabilistic connectivity map of the SLF in Talairach coordinates. Two coronal slices (Talairach coordinate coronal slices D and G) and 1 axial slice (Talairach coordinate axial slice 8) are extracted at the locations indicated by white, pink, and blue arrows, respectively. The high probability regions correspond to Brodmann's areas 44 (white arrow: Broca's area), 40 (pink arrow: supramarginal gyrus), and 22 (blue arrow: Wernicke's area).