Neocortical Evolution: Neuronal Circuits Arise Independently of Lamination

SummaryThe evolutionary origin of the six-layered mammalian neocortex has been controversial. New data on genes with layer-specific expression in mammalian cortex have found an expression pattern in avian forebrain neurons consistent with the view that ‘cortical’ cells and circuits are present in all amniotes, but with different macroarchitectures in birds versus mammals.