Gyral window mapping of typical cortical folding using MRI.

Using the NIH Pediatric MRI Data Repository for normative developmental studies, white matter depth within the gyri of the frontal, temporal, parietal, and occipital lobes, and of the left and right hemisphere was identified for 312 typically developing children and young adults (168 male and 144 female) between 4 and 23 years of age. There was no significant age difference between male and female groups overall (F(1,867) = 0.0002; p = 0.99) or per-visit (F(2,867) = 2.18; p = 0.86). There was significant dependence of gyral window upon age (F(1,6544) = 115, p < 0.0001), lobe (F(3,6544) = 229, p < 0.0001), hemisphere (F(1,6544) = 5.23, p = 0.022), age*sex (F(1,6544) = 13.8, p = 0.0002), age*lobe (F(3,6544) = 120, p = 0.0001), and age*hemisphere (F(1,6544) = 4.41, p = 0.036). Gyrification increased with age in both males and females in the frontal, temporal and parietal lobes with opposite effects observed in the occipital lobe. Relative gyral depth, as measured in this study, was significantly (p < 0.0001) inversely correlated with gyrification index. Previous studies relate gyral window measurements to the differential expression of short and long corticocortical projections. Our results therefore suggest that the pattern of corticocortical connections is malleable during the first two decades of development.