File:Cellular and morphological defects associated with neuronal migration disorders.png

(A) Schematics highlighting the cellular basis of NMDs in the adult human cortex, showing the different cortical layers and neuronal migrations. Single ectopic neurons are shown in grey and the affected structures or processes are indicated. (B) Schematic showing the MRI-detectable morphological defects in the adult human brain that are caused by the cellular defects of each NMD. Ectopically located clusters of affected neurons are shown as greyshading. Lissencephaly type I is characterized bya smooth brain surface and a simplified fourlayered cortex (indicated by green shading). In subcortical band heterotopia, the cortex contains an additional band of grey matter underneath the white matter. Periventricular heterotopia is characterized by clusters (nodular) or sheets (laminar) of neurons accumulating at the ventricles underneath a normal cortex. In lissencephaly type II, neuronsovermigrate ontothecorticalsurface. Schematicsareadapted fromMRIimages,seee.g.BizzottoandFrancis,2015;Francisetal., 2006; Guerrini and Parrini, 2010. IKNM, interkinetic nuclear migration; RG, radial glia; RNM, radial neuronal migration; TNM, tangential neuronal migration.