Diffusion Tensor Imaging Metrics Reveal Pronounced Hemispheric Asymmetry in Major White Matter Tracts.
TL;DR
Widespread hemispheric asymmetries were observed across multiple pathways, which may reflect distinct hemispheric functional specialization and the neurological basis of lateralized functions.
Abstract
ABSTRACT
Aim
To determine hemispheric asymmetries in major white matter tracts using diffusion tensor imaging (DTI) metrics and morphometric measurements, as comprehensive multitract analyses remain limited. MATERIAL and
Methods
Diffusion MRI data from 102 healthy adults enrolled in the Human Connectome Project (HCP) were analyzed using DSI Studio to reconstruct 17 major white- matter tracts bilaterally. For each tract, diffusion metrics (fractional anisotropy [FA], mean diffusivity [MD], radial diffusivity [RD], axial diffusivity [AD], quantitative anisotropy [QA], isotropic value [ISO], restricted diffusion imaging [RDI], and normalized RDI [nrdı]) and morphometric parameters (fiber count, mean length, trunk volume, branch volume, total volume, and termination region areas) were quantified. Paired t-tests compared left-right hemispheric differences. Multiple comparison corrections were performed with the Benjamini-Krieger-Yekutieli procedure, and effect sizes were reported as Cohen's d.
Results
Significant hemispheric asymmetries were observed in most tracts. FA was significantly higher in the left hemisphere (p<0.001) for the arcuate fasciculus (AF), inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), and uncinate fasciculus (UF). Mean diffusivity (MD) demonstrated left dominance in the UF and SLF2-3 (p=0.009). QA was predominantly left- lateralized across multiple tracts, including AF, IFOF, ILF, and frontal aslant tract (FAT) (p<0.01, Cohen's d: 0.42 to 1.17), except for the vertical occipital fasciculus (VOF), where rightward dominance was noted (Cohen's d: -0.55). Tract-trunk-branch volumes were predominantly left-lateralized in frontal lobe pathways such as AF, SLF1, SLF2, FAT, and UF (p<0.01). Rightward dominance was observed in SLF3, parietal aslant tract (PAT), IFOF, ILF, and middle longitudinal fasciculus (MLF) (p<0.05). Similar asymmetries were observed in termination region areas, fiber counts, and fiber lengths (p<0.001).
Conclusion
Widespread hemispheric asymmetries were observed across multiple pathways. Such asymmetry may reflect distinct hemispheric functional specialization and the neurological basis of lateralized functions.