Age-related regional variations of the corpus callosum identified by diffusion tensor tractography

The corpus callosum is the largest white matter connection in the human brain, and an understanding of its evolution with age in healthy individuals is one crucial aspect for determining its role in cognition and disease. Diffusion tensor imaging (DTI) allows for investigation of age-related callosal changes since tractography can both virtually reconstruct the segments of the corpus callosum in vivo based on unique target cortical regions, and provide quantitative diffusion parameters reflecting tissue microstructure. DTI tractography was used to subdivide the corpus callosum into seven distinct sections based on unique target areas (i.e., orbital frontal, anterior frontal, superior frontal, superior parietal, posterior parietal, temporal, and occipital) in a very large number of healthy volunteers (n=315) across a wide age range (5-59 years). Both fractional anisotropy (FA) and mean diffusivity (MD) changes with respect to age were fit with Poisson curves, showing increasing FA and decreasing MD during childhood and adolescence and slightly slower decreases of FA and increases of MD at older ages. Age at peak FA values and minimum MD values varied from 21 to 44 years, and an overall "outer-to-inner" trend was observed in which the anterior and posterior regions peaked earlier than central areas. In addition to these maturational trends of diffusion parameters reflecting the microstructural changes in the healthy corpus callosum over a large age range spanning childhood to older adulthood, these results can provide a baseline for identifying the presence and timing of callosal abnormalities in various brain disorders.