Investigating the association between cortical morphological features and the properties of underlying WM tracts in healthy young adults

Quantitative measures of gray matter (GM) and white matter (WM) can be derived from structural and diffusion Magnetic Resonance Imaging (MRI) to study the cerebral cortex and WM projections. Previous multimodal research in patient populations suggests that changes in GM or WM properties propagate to the other tissue type in anatomically connected regions. The association between GM and WM measures is poorly understood, especially in healthy subjects. Addressing this gap is important because the relationship between GM and WM measures may vary over the lifespan where MRI measures may reflect different underlying mechanisms. The primary purpose of this research was to determine the relationship between GM and associated WM in healthy young adults. It was hypothesized that lower cortical morphometric measures would be associated with lower tract volume and WM micro-structural integrity. These relationships were examined using a surface and tract based approach with a subset of the Human Connectome Project dataset. The cortical surface and 16 known WM pathways were reconstructed. The two WM tract endings for each pathway were projected onto the cortical surface to identify associated GM regions. The WM volume and average fractional anisotropy (FA) were computed for each reconstructed tract of interest (TOI). The cortical thickness, surface area, GM volume and curvature measures were extracted for each corresponding GM region of interest (ROI). The magnitude, direction and significance of the Spearman's Rank Correlation coefficients were used to evaluate the association between GM and WM measures from structurally connected TOIs and ROIs. The most noteworthy findings were the relationships between surface area and WM properties and GM volume and WM properties. Surface area and GM volume were consistently positively correlated with WM volume. These correlations varied from weak to strong and reached significance in nearly all regions examined across the brain. Surface area and GM volume also demonstrated a weak to moderate negative correlation with tract average FA which was significant in over 40\% of the brain regions examined. The relationships between other GM and WM measures were inconclusive with a lack of supporting evidence. Characterizing these relationships may lead to easier detection of abnormal relationships.