(1) These features indicate that unlayered polymicrogyria is produced by circulatory failure occurring before the end of the period of neuroblast migration to the cortical plate.
(2) The cortical dysplasia includes: (1) thin unlayered cortical mantle with radial disposition but no horizontal organisation of the neurons; (2) microgyria with fused molecular layers; and (3) persisting transitory cells in the molecular layer (Cajal-Retzius cells, subpial granular layer).
(3) Two different conventional (acid-base) glass-ionomers were studied with the use of layered and unlayered specimens of dimensions 6 mm (height) x 4 mm (diameter) and 12 mm (height) x 6 mm (diameter).
(4) In type 2 dysplasia, or unlayered micropolygyria, individual cells showed relative paucity of lateral dendritic arborization.
(5) Unlayered polymicrogyria was analyzed in four patients with established lesions and in one 19- to 20-week-old fetus with lesions in a formative stage whose mother had suffered a serious accident two weeks before.
(6) In the unlayered, ventral cochlear nucleus, however, neurons carry information in their temporal firing patterns.
(7) Three anatomical cases of unlayered polymicrogyria associated with agenesis of the corpus callosum and heterotopias are presented.