MRI Analysis of Gyral Window In Normal Brain Development and Its Implications for Studies In Autism

Background: Autism spectrum disorder (ASD) is a pervasive developmental disorder (PDD) that is clinically and qualitatively diagnosed as having impairment in social interaction, communication and repetitive behavior. There is no known cause or cure for ASD. Limited sample size, narrow age range, lack of resources and an inability to duplicate findings of individual studies has made it difficult to assess brain development in autistic individuals as compared to typical or control individuals.

Objectives: To measure the gyrification of cerebral cortex in MRI scans using normalized gyral window depth measurements.

Methods: Using Release 4.0 of the NIH Pediatric MRI Data Repository for normative developmental studies, we measured gyrification by identifying the normalized gyral window depth of 410 typically-developing children ages 4.8 to 22.3 (215 males and 195 females). Of these, 150 (82 males and 68 females) provided MRI data at three visits; 163 (83 males and 80 females) provided MRI data at two visits; and 97 (50 males and 47 females) provided only one MRI scan. Gyral white matter was segmented by lobe using the parameters established by the NIH. A Euclidean distance map (EDM) of gyral white matter was constructed using MatLab in a total of 873 MRI scans from the 410 subjects collectively. Measurement of gyral shape was identified by calculating the d tilde of each segment. The size of the d tilde correlates to the amount of gyrification in which the smaller the d tilde, the greater the gyrification; likewise, the larger the d tide, the lesser the gyrification.

Results: Gyral window measurements indicated that gyrification increased with age in both males and females in the frontal, temporal and parietal lobes and that gyrification decreased with age in both males and females in the occipital lobe. 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).

Conclusions: GI is a morphometric index that varies according to age, hemisphere and lobe examined. Its dependence on lobe and hemispheric side suggests its usefulness in studies of cerebral dominance. The results help explain why gyral window measurements have provided for statistically significant distinctions between the brains of autistic and controls individuals.