The emergence and evolution of mammalian neocortex

Trends Neurosci. 1995 Sep;18(9):373-9. doi: 10.1016/0166-2236(95)93932-n.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Animals
  • Biological Evolution*
  • Cerebral Cortex / anatomy & histology
  • Cerebral Cortex / physiology*
  • Humans
  • Mammals / physiology*
  • Visual Cortex / anatomy & histology
  • Visual Cortex / physiology