title: The emergence and evolution of mammalian neocortex.
abstract: Cortical variation in mammals and other terrestrial vertebrates, re-examined by current comparative methodology (out-group analysis), indicates that separate lateral (olfactory), dorsal and medial (hippocampal) pallial or cortical formations arose with the origin of vertebrates. Although the exact origin of mammalian isocortex (so-called neocortex) is still disputed, it appears that the earliest mammals already had a six-layered isocortex with ten to 20 functional subdivisions. Among placental mammals, at least, isocortex has expanded numerous times, producing additional cortical subdivisions. Because these expansions were independent transformations of a simpler cortex, they produced subdivisions that are not homologous.
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000502:physiology*; D006801:Humans; D008322:Mammals / Q000502:physiology*; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology