Reduced cortical folding in mental retardation

Mental retardation (MR) is a developmental disorder associated with impaired cognitive functioning and deficits in adaptive behavior. Using a 2D ROI-based Gyrification Index, a preliminary study reported significantly reduced gyrification in pre-frontal lobe in MR. The purpose of this study is to further investigate the abnormalities of cortical gyrification in MR and to explore the possible causes of these abnormalities.Thirteen patients with MR and twenty-six demographically matched healthy controls were included in this study. A 3D surface-based local Gyrification Index (lGI) was calculated as a measure to quantify gyrification. Then vertex-by-vertex contrasts of lGI were performed between patients with MR and normal controls. Statistical analysis showed that patients with MR had significantly reduced lGI in multiple brain regions compared with healthy controls. These regions include the lateral and medial prefrontal cortices, the right superior temporal gyrus, the left superior parietal lobe, the bilateral insular and their adjacent cortices as well as visual and motor cortices. The observed abnormal pattern of cortical gyrification revealed by significant reduction of lGI in multiple brain regions might reflect the developmental disturbance in intracortical organization and cortical connectivities in MR.